6.0.4.0

This reverts commit 67d38090ed.

.github/CODEOWNERS

@@ -1 +1,4 @@
-* @epoberezkin @efim-poberezkin
+* @epoberezkin @spaced4ndy
+/Dockerfile @shumvgolove
+/scripts/docker/ @shumvgolove
+/scripts/main/ @shumvgolove

.github/workflows/build.yml

@@ -11,23 +11,30 @@ on:
 
 jobs:
   build:
-    name: build-${{ matrix.os }}
+    name: build-${{ matrix.os }}-${{ matrix.ghc }}
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-18.04
           - os: ubuntu-20.04
+            platform_name: 20_04-x86-64
+            ghc: "8.10.7"
+          - os: ubuntu-20.04
+            platform_name: 20_04-x86-64
+            ghc: "9.6.3"
+          - os: ubuntu-22.04
+            platform_name: 22_04-x86-64
+            ghc: "9.6.3"
     steps:
       - name: Clone project
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Setup Haskell
-        uses: haskell/actions/setup@v1
+        uses: haskell-actions/setup@v2
         with:
-          ghc-version: "8.10.7"
-          cabal-version: "latest"
+          ghc-version: ${{ matrix.ghc }}
+          cabal-version: "3.10.1.0"
 
       - name: Cache dependencies
         uses: actions/cache@v2
@@ -42,20 +49,21 @@ jobs:
         run: cabal build --enable-tests
 
       - name: Test
-        if: matrix.os == 'ubuntu-18.04'
-        timeout-minutes: 30
+        timeout-minutes: 40
         shell: bash
         run: cabal test --test-show-details=direct
 
       - name: Prepare binaries
-        if: startsWith(github.ref, 'refs/tags/v') && matrix.os == 'ubuntu-20.04'
+        if: startsWith(github.ref, 'refs/tags/v')
         shell: bash
         run: |
-          mv $(cabal list-bin smp-server) smp-server-ubuntu-20_04-x86-64
-          mv $(cabal list-bin ntf-server) ntf-server-ubuntu-20_04-x86-64
+          mv $(cabal list-bin smp-server) smp-server-ubuntu-${{ matrix.platform_name}}
+          mv $(cabal list-bin ntf-server) ntf-server-ubuntu-${{ matrix.platform_name}}
+          mv $(cabal list-bin xftp-server) xftp-server-ubuntu-${{ matrix.platform_name}}
+          mv $(cabal list-bin xftp) xftp-ubuntu-${{ matrix.platform_name}}
 
       - name: Build changelog
-        if: startsWith(github.ref, 'refs/tags/v') && matrix.os == 'ubuntu-20.04'
+        if: startsWith(github.ref, 'refs/tags/v') && matrix.os == 'ubuntu-22.04'
         id: build_changelog
         uses: mikepenz/release-changelog-builder-action@v1
         with:
@@ -67,7 +75,7 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Create release
-        if: startsWith(github.ref, 'refs/tags/v') && matrix.os == 'ubuntu-20.04'
+        if: startsWith(github.ref, 'refs/tags/v') && matrix.ghc != '8.10.7'
         uses: softprops/action-gh-release@v1
         with:
           body: |
@@ -78,8 +86,10 @@ jobs:
           prerelease: true
           files: |
             LICENSE
-            smp-server-ubuntu-20_04-x86-64
-            ntf-server-ubuntu-20_04-x86-64
+            smp-server-ubuntu-${{ matrix.platform_name}}
+            ntf-server-ubuntu-${{ matrix.platform_name}}
+            xftp-server-ubuntu-${{ matrix.platform_name}}
+            xftp-ubuntu-${{ matrix.platform_name}}
           fail_on_unmatched_files: true
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/docker-image.yml

@@ -0,0 +1,50 @@
+name: Build and push Docker image to Docker Hub
+
+on:
+  push:
+    tags:
+      - "v*"
+
+jobs:
+  build-and-push:
+    name: Build and push Docker image
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - app: smp-server
+            app_port: 5223
+          - app: xftp-server
+            app_port: 443 
+    steps:
+      - name: Clone project
+        uses: actions/checkout@v3
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v2
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_PASSWORD }}
+
+      - name: Extract metadata for Docker image
+        id: meta
+        uses: docker/metadata-action@v4
+        with:
+          images: ${{ secrets.DOCKERHUB_USERNAME }}/${{ matrix.app }}
+          flavor: |
+            latest=auto
+          tags: |
+            type=semver,pattern=v{{version}}
+            type=semver,pattern=v{{major}}.{{minor}}
+            type=semver,pattern=v{{major}}
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v4
+        with:
+          push: true
+          build-args: |
+            APP=${{ matrix.app }}
+            APP_PORT=${{ matrix.app_port }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}

.gitignore

@@ -7,3 +7,7 @@ dist-newstyle/
 
 cabal.project.local
 cabal.project.local~
+
+.hpc/
+*.tix
+.coverage

.hlint.yaml

@@ -0,0 +1 @@
+- ignore: {name: "Use underscore"}

CHANGELOG.md

@@ -1,3 +1,467 @@
+# 6.0.4
+
+SMP server:
+- better performance/memory: fewer map updates on re-subscriptions (#1297), split and reduce STM transactions (#1294)
+- send DELD when subscribed queue is deleted (#1312)
+- add created/updated/used date to queues to manage expiration (#1306)
+
+XFTP server: truncate file creation time to 1 hour (#1310)
+
+Servers:
+- bind control port only to 127.0.0.1 for better security in case of firewall misconfiguration (#1280)
+- reduce memory used for period stats (#1298)
+
+Agent: process last notification from list (#1307)
+- report receive file error with redirected file ID, when redirect is present (#1304)
+- special error when deleted user record is not in database (#1303)
+- fix race when sending a message to the deleted connection (#1296)
+- support for multiple messages in a single notification
+
+Ntf server:
+- only use SOCKS proxy for servers without public address (#1314)
+
+# 6.0.3
+
+Agent:
+- fix possible stuck queue rotation (#1290).
+
+SMP server:
+- batch END responses when subscribed client switches to reduce server and client traffic.
+- reduce STM transactions for better performance.
+- add stats for END events and for SUB/DEL event batches.
+- remove "expensive" stats to save memory.
+
+# 6.0.2
+
+SMP agent:
+- fix stuck connection commands when a server is not responding.
+- store query errors, reduce slow query threshold to 1ms.
+
+Notification server:
+- reduce PING interval to 1 minute.
+- fix subscriptions disabled on race condition (only mark subscriptions with END status when received via the active connection).
+
+# 6.0.1
+
+SMP agent:
+- support changing user of the new connection.
+- do not start delivery workers when there are no messages to deliver.
+- enable notifications for all connections.
+- combine database transactions when subscribing.
+
+SMP server:
+- safe compacting of store log.
+- fix possible race when creating client that might lead to memory leak.
+
+Dependencies: upgrade tls to 1.9
+
+# 6.0.0
+
+Version 6.0.0.8
+
+Agent:
+- enabled fast handshake support.
+- batch-send multiple messages in each connection.
+- resume subscriptions as soon as agent moves to foreground or as network connection resumes.
+- "known" servers to determine whether to use SMP proxy.
+- retry on SMP proxy NO_SESSION error.
+- fixes to notification subscriptions.
+- persistent server statistics.
+- better concurrency.
+
+SMP server:
+- reduce threads usage.
+- additional statistics.
+- improve disabling inactive clients.
+- additional control port commands for monitoring.
+
+Notification server:
+- support onion-only SMP servers.
+
+# 5.8.2
+
+Agent:
+- fast handshake support (disabled).
+- new statistics api.
+
+SMP server:
+- fast handshake support (SKEY command).
+- minor changes to reduce memory usage.
+
+# 5.8.1
+
+Agent:
+- API to reconnect one server.
+- Better error handling of file errors and remote control connection errors.
+- Only start uploading file once all chunks were registered on the servers.
+
+SMP server:
+- additional stats for sent message notifications.
+- fix server page layout.
+
+# 5.8.0
+
+Version 5.8.0.10
+
+SMP server and client:
+- protocol extension to forward messages to the destination servers, to protect sending client IP address and transport session.
+
+Agent:
+- process timed out subscription responses to reduce the number of resubscriptions.
+- avoid sending messages and commands when waiting for response timed out (except batched SUB and DEL commands).
+- fix issue with stuck message reception on slow connection (when response to ACK timed out, and the new message was not processed until resubscribed).
+- fix issue when temporary file sending or receiving error was treated as permanent.
+
+SMP server:
+- include OK responses to all batched SUB requests to reduce subscription timeouts.
+
+XFTP server:
+- report file upload timeout as TIMEOUT, to avoid delivery failure.
+
+# 5.7.6
+
+XFTP agent:
+- treat XFTP handshake timeouts and network errors as temporary, to retry file operations.
+
+# 5.7.5
+
+SMP agent:
+- fail if non-unique connection IDs are passed to sendMessages (to prevent client errors and deadlocks).
+
+# 5.7.4
+
+SMP agent:
+- remove re-subscription timeouts (as they are tracked per operation, and could cause failed subscriptions).
+- reconnect XFTP clients when network settings changes.
+- fix lock contention resulting in stuck subscriptions on network change.
+
+# 5.7.3
+
+SMP/NTF protocol:
+- add ALPN for handshake version negotiation, similar to XFTP (to preserve backwards compatibility with the old clients).
+- upgrade clients to versions v7/v2 of the protocols.
+
+SMP server:
+- faster responses to subscription requests.
+
+XFTP client:
+- fix network exception during file download treated as permanent file error.
+
+SMP agent:
+- do not report subscription timeouts while client is offline.
+
+# 5.7.2
+
+SMP agent:
+- fix connections failing when connecting via link due to race condition on slow network.
+- remove concurrency limit when waiting for connection subscription.
+- remove TLS timeout.
+
+# 5.7.1
+
+SMP agent:
+- increase timeout for TLS connection via SOCKS
+
+# 5.7.0
+
+Version 5.7.0.4
+
+_Please note_: the earliest SimpleX Chat clients supported by this version of the servers is 5.5.3 (released on February 11, 2024).
+
+SMP server:
+- increase max SMP protocol version to 7 (support for deniable authenticators).
+
+NTF server:
+- increase max NTF protocol version to 2 (support for deniable authenticators).
+
+XFTP server:
+- version handshake using ALPN.
+
+SMP agent:
+- increase timeouts for XFTP files.
+- don't send commands after timeout.
+- PQ encryption support.
+
+# 5.6.2
+
+Version 5.6.2.2.
+
+SMP agent:
+- Lower memory consumption (~20-25%).
+- More stable XFTP file uploads and downloads.
+- API to receive network connectivity changes from the apps.
+- to reduce battery consumption: connection attempts interval growing to every 2 hours when app reports as offline.
+- to reduce retries and traffic: 50% increased timeouts when on mobile network.
+
+XFTP server:
+- expire files on start.
+- version negotiation based on TLS ALPN and handshake.
+
+NTF server:
+- reduced downtime by ~100x faster start time.
+- exclude test tokens from statistics.
+
+# 5.6.1
+
+Version 5.6.1.0.
+
+- Much faster iOS notification server start time (fewer skipped notifications).
+- Fix SMP server stored message stats.
+- Prevent overwriting uploaded XFTP files with subsequent upload attempts.
+- Faster base64 encoding/parsing.
+- Control port audit log and authentication.
+
+# 5.6.0
+
+Version 5.6.0.4.
+
+SMP protocol/client/server:
+- support deniable sender command authorization (to be enabled in the next version).
+- remove support for SMP protocol versions (prior to v4, 07/2022).
+
+Agent:
+- optional post-quantum key agreement using sntrup761 in double ratchet protocol.
+- improve performance of deleting multiple connections and files by batching database operations.
+- delay connection deletion to deliver pending messages.
+- API to test for notifications server.
+- remove support for client protocols versions (prior to 10/2022).
+
+XFTP server:
+- restore storage quota in case of failed uploads.
+
+Performance and stability improvements.
+
+# 5.5.3
+
+Agent:
+- notification token API also returns active notifications server.
+- support file descriptions with redirection and file URIs.
+
+Servers:
+- CLI commands for online key and certificate rotation.
+- Configure config and log paths via environment variables.
+
+# 5.5.2
+
+Extensible handshake for clients and SMP/NTF servers (ignore extra data).
+
+# 5.5.1
+
+SMP servers:
+- do not keep stats file open
+- additional stats about currently stored messages
+
+Agent:
+- support multiple notification servers (only one can be used at a time).
+- expire messages after "quota exceeded" error after 7 days (instead of 21 days previously).
+- stabilize message delivery, remove unnecessary subscription retries and traffic.
+- improve database performance for message delivery.
+- fix sockets/memory leak - a very old bug "activated" by improvements in v5.5.0.
+
+# 5.5.0
+
+Code:
+- compatible with GHC 8.10.7 to support compilation for armv7a.
+- migrate to `crypton` from deprecated `cryptonite` (the seed for DRG is now sha512-hashed).
+- use ChaChaDRG for all random IDs, keys and nonces, only using hashed entropy as seed.
+- more efficient transaction batching in SMP protocol client and server.
+
+Agent:
+- stabilize message reception and delivery, migrate message delivery to database queue.
+- additional event MSGNTF confirming that message received via notification is processed.
+- efficient processing of messages sent to multiple recipients with batched database transactions.
+- new worker abstraction for all queued tasks resilient to race conditions and some database errors.
+- many fixed race conditions.
+- background mode for iOS NSE.
+- additional error reporting to client on critical errors (to be show as alert in the clients).
+- functional api to get worker statistics.
+
+SMP/XFTP servers:
+- fix socket and memory leak on servers with high load (inactive clients without subscriptions are disconnected after set time of inactivity).
+- control port improvements.
+- fix statistics for stored queues, messages and files.
+- make writing to store log atomic (fixes a rare bug in XFTP server).
+
+# 5.4.0
+
+Migrate to GHC 9.6.3
+
+Agent:
+- database improvements:
+  - track slow queries.
+  - better performance.
+  - "busy" error handling.
+  - create parent folder when needed.
+  - support closing and re-opening database.
+- SMP agent improvements
+  - streaming for batched SMP commands.
+  - fix asynchronous JOINing connection.
+  - handle repeating JOINs without failure.
+  - api to get subscribed connections.
+  - return simplex:/ links as invitations.
+  - fix memory leak.
+- XFTP improvements:
+  - suspend when agent is suspended.
+  - support locally encrypted files.
+  - fixes - create empty file, prevent permanent error treated as temporary.
+  - upgrade HTTP2 library (fixes error handling and flow control).
+- Remote control protocol (XRCP)
+
+SMP server:
+- control port commands for GHC threads introspection.
+- allow creating new queues without subscriptions (required for iOS).
+
+XFTP server:
+- allow 64kb file chunks.
+
+NTF server:
+- faster startup.
+
+# 5.3.0
+
+Agent:
+- improve performance, track slow database queries.
+- support delivery receipts.
+
+SMP server:
+- control port
+
+# 5.2.0 (NTF server 1.5.0)
+
+Agent:
+- treat agent INACTIVE error as temporary - fixes failed message delivery in some race conditions.
+- restore connection confirmations after client restart - fixes failed connections.
+- ratchet resynchronization protocol and API.
+- increase connection version to mutually supported by both peers on each received message.
+
+Client:
+- make timeout for batched functions dependent on the number of batches - fixes expiry on large batches.
+
+Servers:
+- add timeout in case of sending TCP traffic and in case of partial delivery of requested blocks to avoid resource leaks.
+
+# 5.1.2, 5.1.3 (NTF server 1.4.1, 1.4.2)
+
+Agent:
+- ACK message on decryption error (fixes stuck message delivery bug)
+- more robust connection switching logic, API to abort switching the address
+
+Notification server:
+- batch subscriptions to SMP servers
+
+# 5.1.1 (NTF server 1.4.0)
+
+Agent:
+- store and check hashes of previous encrypted messages to differentiate between duplicates and decryption errors
+
+Server:
+- larger processing queues
+- expire messages when restoring them
+
+# 5.1.0
+
+XFTP client:
+- check encrypted file exists when uploading
+- remove user ID from deletion API
+
+Agent:
+- vacuum database on migrations
+
+SMP server:
+- configure message expiration time in INI file
+
+# 5.0.0
+
+SimpleX File Transfer Protocol (XFTP):
+- XFTP server
+- XFTP CLI
+- support XFTP in the agent
+
+Other changes:
+- preserve retry interval for sending messages on agent restarts
+- support IPv6 in the servers and in the agent
+- support for 32-bit platforms
+
+Read more about XFTP in this post: https://simplex.chat/blog/20230301-simplex-file-transfer-protocol.html
+
+# 4.4.1
+
+SMP agent:
+
+- fix handling of server addresses.
+- prevent message delivery getting stuck on IO error in SMP client.
+
+# 4.4.0
+
+SMP agent:
+
+- support multiple user profiles with transport session isolation.
+- support optional transport isolation per connection.
+- batch connection deletion
+- improve asynchronous connection deletion – it may now be completed after the client is restarted as well.
+- improve subscription logic to retry if initial attempt fails.
+- end SMP client connection after a number of failed PINGs (default is 3).
+
+# 4.3.0
+
+SMP server:
+
+- additional server usage statistics.
+
+SMP agent:
+
+- increase retry interval when sending messages after ERR QUOTA.
+
+# 4.2.0
+
+SMP agent and server:
+
+- reduce sender traffic in cases when queue quota is exceeded:
+  - server sends quota exceeded message to the recipient when sender receives ERR QUOTA.
+  - recipient sends QCONT message to the send once the queue is drained (via reply queue).
+  - sender retry delays are increased, reducing traffic, but sender instantly resumes delivery where QCONT is received.
+
+SMP server:
+
+- increase internal queue sizes.
+
+SMP agent:
+
+- deduplicate connection IDs in connect/disconnect responses.
+- unit tests for Crypto.hs.
+- fix connection switch to another queue: correctly set primary send queue.
+
+Notification server (v1.3.0):
+
+- check token status when sending verification notification.
+
+# 4.1.0
+
+SMP agent and server:
+
+- option to toggle TLS handshake error logs (disabled by default).
+
+SMP agent:
+
+- include server address in BROKER error.
+- api to get hash of double ratchet associated data (for connection verification).
+- api to get agent statistics.
+
+# 4.0.0
+
+SMP server:
+
+- Basic authentication. The server address can now include an optional password that is required to create messaging queues, so the contacts who message you will not be able to receive messages via your server, unless you share with them the address with the password. It is recommended to enable basic authentication on all private servers by adding `create_password` parameter into AUTH section of server INI file (the previously deployed servers do not have this section, you need to add it).
+- Disable creating new queues completely with `new_queues: off` parameter in AUTH section of INI file - it can be used to simplify migrating the existing connections to another server.
+- Updated server CLI with changed defaults:
+  - interactive server initialization, use -y flag to initialize the server non-interactively.
+  - store log is now enabled by default, so messaging queues and messages are restored when the server is restarted (to restore undelivered messages the server needs to be stopped with SIGINT signal).
+  - a random password is now generated by default during the server initialization.
+
+SMP agent:
+
+- API to test SMP servers. It connects to the server, creates and deletes a messaging queue. The new SimpleX Chat client uses this API to allow you to test that you have the correct server address, with the valid certificate fingerprint and password, before enabling the new server.
+
 # 3.4.0
 
 SMP agent:
@@ -42,9 +506,9 @@ SMP server and agent:
 
 SMP server:
 
-- restore undeliverd messages when the server is restarted.
+- restore undelivered messages when the server is restarted.
 - SMP protocol v3 to support push notification:
-  - updated SEND and MSG to add message flags (for notification flag that contros whether the notification is sent and for any future extensions) and to move message meta-data sent to the recipient into the encrypted envelope.
+  - updated SEND and MSG to add message flags (for notification flag that confirm whether the notification is sent and for any future extensions) and to move message meta-data sent to the recipient into the encrypted envelope.
   - update NKEY and NID to add e2e encryption keys (for the notification meta-data encryption between SMP server and the client), and update NMSG to include this meta-data.
   - update ACK command to include message ID (to avoid acknowledging unprocessed message).
   - add NDEL commands to remove notification subscription credentials from SMP queue.
@@ -55,7 +519,7 @@ SMP agent:
 - new protocol for duplex connection handshake reducing traffic and connection time.
 - support for SMP notifications server and managing device token.
 - remove redundant FQDN validation from TLS handshake to prepare for access via Tor.
-- support for fully stopping agent and for termporary suspending agent operations.
+- support for fully stopping agent and for temporary suspending agent operations.
 - improve management of duplicate message delivery.
 
 SMP notifications server v1.0:

Dockerfile

@@ -0,0 +1,62 @@
+ARG TAG=22.04
+
+FROM ubuntu:${TAG} AS build
+
+### Build stage
+
+# Install curl and git and simplexmq dependencies
+RUN apt-get update && apt-get install -y curl git build-essential libgmp3-dev zlib1g-dev llvm-12 llvm-12-dev libnuma-dev libssl-dev
+
+# Specify bootstrap Haskell versions
+ENV BOOTSTRAP_HASKELL_GHC_VERSION=9.6.3
+ENV BOOTSTRAP_HASKELL_CABAL_VERSION=3.10.1.0
+
+# Install ghcup
+RUN curl --proto '=https' --tlsv1.2 -sSf https://get-ghcup.haskell.org | BOOTSTRAP_HASKELL_NONINTERACTIVE=1 sh
+
+# Adjust PATH
+ENV PATH="/root/.cabal/bin:/root/.ghcup/bin:$PATH"
+
+# Set both as default
+RUN ghcup set ghc "${BOOTSTRAP_HASKELL_GHC_VERSION}" && \
+    ghcup set cabal "${BOOTSTRAP_HASKELL_CABAL_VERSION}"
+
+COPY . /project
+WORKDIR /project
+
+ARG APP
+ARG APP_PORT
+RUN if [ -z "$APP" ] || [ -z "$APP_PORT" ]; then printf "Please spcify \$APP and \$APP_PORT build-arg.\n"; exit 1; fi
+
+# Compile app
+RUN cabal update
+RUN cabal build exe:$APP
+
+# Create new path containing all files needed
+RUN mkdir /final
+WORKDIR /final
+
+# Strip the binary from debug symbols to reduce size
+RUN bin=$(find /project/dist-newstyle -name "$APP" -type f -executable) && \
+    mv "$bin" ./ && \
+    strip ./"$APP" &&\
+    mv /project/scripts/docker/entrypoint-"$APP" ./entrypoint
+
+### Final stage
+FROM ubuntu:${TAG}
+
+# Install OpenSSL dependency
+RUN apt-get update && apt-get install -y openssl libnuma-dev
+
+# Copy compiled app from build stage
+COPY --from=build /final /usr/local/bin/
+
+# Open app listening port
+ARG APP_PORT
+EXPOSE $APP_PORT
+
+# simplexmq requires using SIGINT to correctly preserve undelivered messages and restore them on restart
+STOPSIGNAL SIGINT
+
+# Finally, execute helper script
+ENTRYPOINT [ "/usr/local/bin/entrypoint" ]

README.md

@@ -90,19 +90,158 @@ You can either run your own SMP server locally or deploy using [Linode StackScri
 
 It's the easiest to try SMP agent via a prototype [simplex-chat](https://github.com/simplex-chat/simplex-chat) terminal UI.
 
-## Deploy SMP server on Linux
+## Deploy SMP/XFTP servers on Linux
 
-You can run your SMP server as a Linux process, optionally using a service manager for booting and restarts.
+You can run your SMP/XFTP server as a Linux process, optionally using a service manager for booting and restarts.
 
-- For Ubuntu you can download a binary from [the latest release](https://github.com/simplex-chat/simplexmq/releases).
+Notice that `smp-server` and `xftp-server` requires `openssl` as run-time dependency (it is used to generate server certificates during initialization). Install it with your packet manager:
 
-  If you're using other Linux distribution and the binary is incompatible with it, you can build from source using [Haskell stack](https://docs.haskellstack.org/en/stable/README/):
+```sh
+# For Ubuntu
+apt update && apt install openssl
+```
 
-  ```shell
-  curl -sSL https://get.haskellstack.org/ | sh
-  ...
-  stack install
-  ```
+### Install binaries
+
+#### Using Docker
+
+On Linux, you can deploy smp and xftp server using Docker. This will download image from [Docker Hub](https://hub.docker.com/r/simplexchat).
+
+1. Create directories for persistent Docker configuration:
+
+   ```sh
+   mkdir -p $HOME/simplex/{xftp,smp}/{config,logs} && mkdir -p $HOME/simplex/xftp/files
+   ```
+
+2. Run your Docker container.
+
+   - `smp-server`
+   
+     You must change **your_ip_or_domain**. `-e "pass=password"` is optional variable to password-protect your `smp` server:
+     ```sh
+     docker run -d \
+         -e "ADDR=your_ip_or_domain" \
+         -e "PASS=password" \
+         -p 5223:5223 \
+         -v $HOME/simplex/smp/config:/etc/opt/simplex:z \
+         -v $HOME/simplex/smp/logs:/var/opt/simplex:z \
+         simplexchat/smp-server:latest
+     ```
+
+   - `xftp-server`
+   
+     You must change **your_ip_or_domain** and **maximum_storage**.
+     ```sh
+     docker run -d \
+         -e "ADDR=your_ip_or_domain" \
+         -e "QUOTA=maximum_storage" \
+         -p 443:443 \
+         -v $HOME/simplex/xftp/config:/etc/opt/simplex-xftp:z \
+         -v $HOME/simplex/xftp/logs:/var/opt/simplex-xftp:z \
+         -v $HOME/simplex/xftp/files:/srv/xftp:z \
+         simplexchat/xftp-server:latest
+     ```
+
+#### Using installation script
+
+**Please note** that currently, only Ubuntu distribution is supported.
+
+You can install and setup servers automatically using our script:
+
+```sh
+curl --proto '=https' --tlsv1.2 -sSf https://raw.githubusercontent.com/simplex-chat/simplexmq/stable/install.sh -o simplex-server-install.sh \
+&& if echo 'c90886104cd640b2ed64921dba80e90691db36788e8d6dcc13d8f33f92f0ea54 simplex-server-install.sh' | sha256sum -c; then chmod +x ./simplex-server-install.sh && ./simplex-server-install.sh; rm ./simplex-server-install.sh; else echo "SHA-256 checksum is incorrect!" && rm ./simplex-server-install.sh; fi
+```
+
+### Build from source
+
+#### Using Docker
+
+> **Please note:** to build the app use source code from [stable branch](https://github.com/simplex-chat/simplexmq/tree/stable).
+
+On Linux, you can build smp server using Docker.
+
+1. Build your images:
+
+   ```sh
+   git clone https://github.com/simplex-chat/simplexmq
+   cd simplexmq
+   git checkout stable
+   DOCKER_BUILDKIT=1 docker build -t local/smp-server --build-arg APP="smp-server" --build-arg APP_PORT="5223" . # For xmp-server
+   DOCKER_BUILDKIT=1 docker build -t local/xftp-server --build-arg APP="xftp-server" --build-arg APP_PORT="443" . # For xftp-server
+   ```
+
+2. Create directories for persistent Docker configuration:
+
+   ```sh
+   mkdir -p $HOME/simplex/{xftp,smp}/{config,logs} && mkdir -p $HOME/simplex/xftp/files
+   ```
+
+3. Run your Docker container.
+
+   - `smp-server`
+   
+     You must change **your_ip_or_domain**. `-e "pass=password"` is optional variable to password-protect your `smp` server:
+     ```sh
+     docker run -d \
+         -e "ADDR=your_ip_or_domain" \
+         -e "PASS=password" \
+         -p 5223:5223 \
+         -v $HOME/simplex/smp/config:/etc/opt/simplex:z \
+         -v $HOME/simplex/smp/logs:/var/opt/simplex:z \
+         simplexchat/smp-server:latest
+     ```
+
+   - `xftp-server`
+   
+     You must change **your_ip_or_domain** and **maximum_storage**.
+     ```sh
+     docker run -d \
+         -e "ADDR=your_ip_or_domain" \
+         -e "QUOTA=maximum_storage" \
+         -p 443:443 \
+         -v $HOME/simplex/xftp/config:/etc/opt/simplex-xftp:z \
+         -v $HOME/simplex/xftp/logs:/var/opt/simplex-xftp:z \
+         -v $HOME/simplex/xftp/files:/srv/xftp:z \
+         simplexchat/xftp-server:latest
+     ```
+
+#### Using your distribution
+
+1. Install dependencies and build tools (`GHC`, `cabal` and dev libs):
+
+   ```sh
+   # On Ubuntu. Depending on your distribution, use your package manager to determine package names.
+   sudo apt-get update && apt-get install -y build-essential curl libffi-dev libffi7 libgmp3-dev libgmp10 libncurses-dev libncurses5 libtinfo5 pkg-config zlib1g-dev libnuma-dev libssl-dev
+   export BOOTSTRAP_HASKELL_GHC_VERSION=9.6.3
+   export BOOTSTRAP_HASKELL_CABAL_VERSION=3.10.3.0
+   curl --proto '=https' --tlsv1.2 -sSf https://get-ghcup.haskell.org | BOOTSTRAP_HASKELL_NONINTERACTIVE=1 sh
+   ghcup set ghc "${BOOTSTRAP_HASKELL_GHC_VERSION}"
+   ghcup set cabal "${BOOTSTRAP_HASKELL_CABAL_VERSION}"
+   source ~/.ghcup/env
+   ```
+
+2. Build the project:
+
+   ```sh
+   git clone https://github.com/simplex-chat/simplexmq
+   cd simplexmq
+   git checkout stable
+   cabal update
+   cabal build exe:smp-server exe:xftp-server
+   ```
+
+3. List compiled binaries:
+
+   `smp-server`
+   ```sh
+   cabal list-bin exe:smp-server
+   ```
+
+   `xftp-server`
+   ```sh
+   cabal list-bin exe:xftp-server 
+   ```
 
 - Initialize SMP server with `smp-server init [-l] -n <fqdn>` or `smp-server init [-l] --ip <ip>` - depending on how you initialize it, either FQDN or IP will be used for server's address.
 
@@ -112,14 +251,6 @@ You can run your SMP server as a Linux process, optionally using a service manag
 
 See [this section](#smp-server) for more information. Run `smp-server -h` and `smp-server init -h` for explanation of commands and options.
 
-<img alt="Docker" src="./img/docker.svg" align="right" width="200">
-
-## Deploy SMP server with Docker
-
-SMP server could also be deployed using `Docker`.
-
-See: [`scripts/docker`](./scripts/docker/)
-
 [<img alt="Linode" src="./img/linode.svg" align="right" width="200">](https://cloud.linode.com/stackscripts/748014)
 
 ## Deploy SMP server on Linode

apps/ntf-server/Main.hs

@@ -1,88 +1,21 @@
-{-# LANGUAGE DuplicateRecordFields #-}
-{-# LANGUAGE NamedFieldPuns #-}
-{-# LANGUAGE OverloadedStrings #-}
-
 module Main where
 
 import Control.Logger.Simple
-import Data.Functor (($>))
-import Data.Ini (lookupValue)
-import Simplex.Messaging.Client.Agent (defaultSMPClientAgentConfig)
-import Simplex.Messaging.Notifications.Server (runNtfServer)
-import Simplex.Messaging.Notifications.Server.Env (NtfServerConfig (..))
-import Simplex.Messaging.Notifications.Server.Push.APNS (defaultAPNSPushClientConfig)
-import Simplex.Messaging.Server.CLI (ServerCLIConfig (..), protocolServerCLI)
-import System.FilePath (combine)
+import Simplex.Messaging.Server.CLI (getEnvPath)
+import Simplex.Messaging.Notifications.Server.Main
 
-cfgPath :: FilePath
-cfgPath = "/etc/opt/simplex-notifications"
+defaultCfgPath :: FilePath
+defaultCfgPath = "/etc/opt/simplex-notifications"
 
-logPath :: FilePath
-logPath = "/var/opt/simplex-notifications"
+defaultLogPath :: FilePath
+defaultLogPath = "/var/opt/simplex-notifications"
 
 logCfg :: LogConfig
 logCfg = LogConfig {lc_file = Nothing, lc_stderr = True}
 
 main :: IO ()
 main = do
-  setLogLevel LogDebug -- change to LogError in production
-  withGlobalLogging logCfg $ protocolServerCLI ntfServerCLIConfig runNtfServer
-
-ntfServerCLIConfig :: ServerCLIConfig NtfServerConfig
-ntfServerCLIConfig =
-  let caCrtFile = combine cfgPath "ca.crt"
-      serverKeyFile = combine cfgPath "server.key"
-      serverCrtFile = combine cfgPath "server.crt"
-   in ServerCLIConfig
-        { cfgDir = cfgPath,
-          logDir = logPath,
-          iniFile = combine cfgPath "ntf-server.ini",
-          storeLogFile = combine logPath "ntf-server-store.log",
-          caKeyFile = combine cfgPath "ca.key",
-          caCrtFile,
-          serverKeyFile,
-          serverCrtFile,
-          fingerprintFile = combine cfgPath "fingerprint",
-          defaultServerPort = "443",
-          executableName = "ntf-server",
-          serverVersion = "SMP notifications server v1.2.0",
-          mkIniFile = \enableStoreLog defaultServerPort ->
-            "[STORE_LOG]\n\
-            \# The server uses STM memory for persistence,\n\
-            \# that will be lost on restart (e.g., as with redis).\n\
-            \# This option enables saving memory to append only log,\n\
-            \# and restoring it when the server is started.\n\
-            \# Log is compacted on start (deleted objects are removed).\n\
-            \enable: "
-              <> (if enableStoreLog then "on" else "off")
-              <> "\n\
-                 \log_stats: off\n\n\
-                 \[TRANSPORT]\n\
-                 \port: "
-              <> defaultServerPort
-              <> "\n\
-                 \websockets: off\n",
-          mkServerConfig = \storeLogFile transports ini ->
-            let settingIsOn section name = if lookupValue section name ini == Right "on" then Just () else Nothing
-                logStats = settingIsOn "STORE_LOG" "log_stats"
-             in NtfServerConfig
-                  { transports,
-                    subIdBytes = 24,
-                    regCodeBytes = 32,
-                    clientQSize = 16,
-                    subQSize = 64,
-                    pushQSize = 128,
-                    smpAgentCfg = defaultSMPClientAgentConfig,
-                    apnsConfig = defaultAPNSPushClientConfig,
-                    inactiveClientExpiration = Nothing,
-                    storeLogFile,
-                    resubscribeDelay = 50000, -- 50ms
-                    caCertificateFile = caCrtFile,
-                    privateKeyFile = serverKeyFile,
-                    certificateFile = serverCrtFile,
-                    logStatsInterval = logStats $> 86400, -- seconds
-                    logStatsStartTime = 0, -- seconds from 00:00 UTC
-                    serverStatsLogFile = combine logPath "ntf-server-stats.daily.log",
-                    serverStatsBackupFile = logStats $> combine logPath "ntf-server-stats.log"
-                  }
-        }
+  setLogLevel LogInfo
+  cfgPath <- getEnvPath "NTF_SERVER_CFG_PATH" defaultCfgPath
+  logPath <- getEnvPath "NTF_SERVER_LOG_PATH" defaultLogPath
+  withGlobalLogging logCfg $ ntfServerCLI cfgPath logPath

apps/smp-agent/Main.hs

@@ -1,33 +1,46 @@
 {-# LANGUAGE DuplicateRecordFields #-}
-{-# LANGUAGE NumericUnderscores #-}
+{-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TypeApplications #-}
 
 module Main where
 
 import Control.Logger.Simple
+import Data.ByteArray (ScrubbedBytes)
 import qualified Data.List.NonEmpty as L
+import qualified Data.Map.Strict as M
 import Simplex.Messaging.Agent.Env.SQLite
 import Simplex.Messaging.Agent.Server (runSMPAgent)
+import Simplex.Messaging.Agent.Store.SQLite (MigrationConfirmation (..))
 import Simplex.Messaging.Client (defaultNetworkConfig)
 import Simplex.Messaging.Transport (TLS, Transport (..))
 
 cfg :: AgentConfig
 cfg = defaultAgentConfig
 
+agentDbFile :: String
+agentDbFile = "smp-agent.db"
+
+agentDbKey :: ScrubbedBytes
+agentDbKey = ""
+
 servers :: InitialAgentServers
 servers =
   InitialAgentServers
-    { smp = L.fromList ["smp://bU0K-bRg24xWW__lS0umO1Zdw_SXqpJNtm1_RrPLViE=@localhost:5223"],
+    { smp = M.fromList [(1, L.fromList ["smp://bU0K-bRg24xWW__lS0umO1Zdw_SXqpJNtm1_RrPLViE=@localhost:5223"])],
       ntf = [],
+      xftp = M.empty,
       netCfg = defaultNetworkConfig
     }
 
 logCfg :: LogConfig
 logCfg = LogConfig {lc_file = Nothing, lc_stderr = True}
 
+-- Warning: this SMP agent server is experimental - it does not work correctly with multiple connected TCP clients in some cases.
 main :: IO ()
 main = do
-  putStrLn $ "SMP agent listening on port " ++ tcpPort (cfg :: AgentConfig)
+  let AgentConfig {tcpPort} = cfg
+  putStrLn $ maybe (error "no agent port") (\port -> "SMP agent listening on port " ++ port) tcpPort
   setLogLevel LogInfo -- LogError
-  withGlobalLogging logCfg $ runSMPAgent (transport @TLS) cfg servers
+  Right st <- createAgentStore agentDbFile agentDbKey False MCConsole
+  withGlobalLogging logCfg $ runSMPAgent (transport @TLS) cfg servers st

apps/smp-server/Main.hs

@@ -1,25 +1,15 @@
-{-# LANGUAGE DuplicateRecordFields #-}
-{-# LANGUAGE NamedFieldPuns #-}
-{-# LANGUAGE NumericUnderscores #-}
-{-# LANGUAGE OverloadedStrings #-}
-
 module Main where
 
 import Control.Logger.Simple
-import Data.Functor (($>))
-import Data.Ini (lookupValue)
-import Simplex.Messaging.Server (runSMPServer)
-import Simplex.Messaging.Server.CLI (ServerCLIConfig (..), protocolServerCLI, readStrictIni)
-import Simplex.Messaging.Server.Env.STM (ServerConfig (..), defaultInactiveClientExpiration, defaultMessageExpiration)
-import Simplex.Messaging.Server.Expiration
-import Simplex.Messaging.Transport (simplexMQVersion, supportedSMPServerVRange)
-import System.FilePath (combine)
+import Simplex.Messaging.Server.CLI (getEnvPath)
+import Simplex.Messaging.Server.Main
+import qualified Static
 
-cfgPath :: FilePath
-cfgPath = "/etc/opt/simplex"
+defaultCfgPath :: FilePath
+defaultCfgPath = "/etc/opt/simplex"
 
-logPath :: FilePath
-logPath = "/var/opt/simplex"
+defaultLogPath :: FilePath
+defaultLogPath = "/var/opt/simplex"
 
 logCfg :: LogConfig
 logCfg = LogConfig {lc_file = Nothing, lc_stderr = True}
@@ -27,83 +17,6 @@ logCfg = LogConfig {lc_file = Nothing, lc_stderr = True}
 main :: IO ()
 main = do
   setLogLevel LogDebug
-  withGlobalLogging logCfg . protocolServerCLI smpServerCLIConfig $ \cfg@ServerConfig {inactiveClientExpiration} -> do
-    putStrLn $ case inactiveClientExpiration of
-      Just ExpirationConfig {ttl, checkInterval} -> "expiring clients inactive for " <> show ttl <> " seconds every " <> show checkInterval <> " seconds"
-      _ -> "not expiring inactive clients"
-    runSMPServer cfg
-
-smpServerCLIConfig :: ServerCLIConfig ServerConfig
-smpServerCLIConfig =
-  let caCrtFile = combine cfgPath "ca.crt"
-      serverKeyFile = combine cfgPath "server.key"
-      serverCrtFile = combine cfgPath "server.crt"
-   in ServerCLIConfig
-        { cfgDir = cfgPath,
-          logDir = logPath,
-          iniFile = combine cfgPath "smp-server.ini",
-          storeLogFile = combine logPath "smp-server-store.log",
-          caKeyFile = combine cfgPath "ca.key",
-          caCrtFile,
-          serverKeyFile,
-          serverCrtFile,
-          fingerprintFile = combine cfgPath "fingerprint",
-          defaultServerPort = "5223",
-          executableName = "smp-server",
-          serverVersion = "SMP server v" <> simplexMQVersion,
-          mkIniFile = \enableStoreLog defaultServerPort ->
-            "[STORE_LOG]\n\
-            \# The server uses STM memory for persistence,\n\
-            \# that will be lost on restart (e.g., as with redis).\n\
-            \# This option enables saving memory to append only log,\n\
-            \# and restoring it when the server is started.\n\
-            \# Log is compacted on start (deleted objects are removed).\n"
-              <> ("enable: " <> (if enableStoreLog then "on" else "off") <> "\n")
-              <> "# Undelivered messages are optionally saved and restored when the server restarts,\n\
-                 \# they are preserved in the .bak file until the next restart.\n"
-              <> ("restore_messages: " <> (if enableStoreLog then "on" else "off") <> "\n")
-              <> ("log_stats: off\n\n")
-              <> "[TRANSPORT]\n"
-              <> ("port: " <> defaultServerPort <> "\n")
-              <> "websockets: off\n\n"
-              <> "[INACTIVE_CLIENTS]\n\
-                 \# TTL and interval to check inactive clients\n\
-                 \disconnect: off\n"
-              <> ("# ttl: " <> show (ttl defaultInactiveClientExpiration) <> "\n")
-              <> ("# check_interval: " <> show (checkInterval defaultInactiveClientExpiration) <> "\n"),
-          mkServerConfig = \storeLogFile transports ini ->
-            let settingIsOn section name = if lookupValue section name ini == Right "on" then Just () else Nothing
-                logStats = settingIsOn "STORE_LOG" "log_stats"
-             in ServerConfig
-                  { transports,
-                    tbqSize = 16,
-                    serverTbqSize = 64,
-                    msgQueueQuota = 128,
-                    queueIdBytes = 24,
-                    msgIdBytes = 24, -- must be at least 24 bytes, it is used as 192-bit nonce for XSalsa20
-                    caCertificateFile = caCrtFile,
-                    privateKeyFile = serverKeyFile,
-                    certificateFile = serverCrtFile,
-                    storeLogFile,
-                    storeMsgsFile =
-                      let messagesPath = combine logPath "smp-server-messages.log"
-                       in case lookupValue "STORE_LOG" "restore_messages" ini of
-                            Right "on" -> Just messagesPath
-                            Right _ -> Nothing
-                            -- if the setting is not set, it is enabled when store log is enabled
-                            _ -> storeLogFile $> messagesPath,
-                    allowNewQueues = True,
-                    messageExpiration = Just defaultMessageExpiration,
-                    inactiveClientExpiration =
-                      settingIsOn "INACTIVE_CLIENTS" "disconnect"
-                        $> ExpirationConfig
-                          { ttl = readStrictIni "INACTIVE_CLIENTS" "ttl" ini,
-                            checkInterval = readStrictIni "INACTIVE_CLIENTS" "check_interval" ini
-                          },
-                    logStatsInterval = logStats $> 86400, -- seconds
-                    logStatsStartTime = 0, -- seconds from 00:00 UTC
-                    serverStatsLogFile = combine logPath "smp-server-stats.daily.log",
-                    serverStatsBackupFile = logStats $> combine logPath "smp-server-stats.log",
-                    smpServerVRange = supportedSMPServerVRange
-                  }
-        }
+  cfgPath <- getEnvPath "SMP_SERVER_CFG_PATH" defaultCfgPath
+  logPath <- getEnvPath "SMP_SERVER_LOG_PATH" defaultLogPath
+  withGlobalLogging logCfg $ smpServerCLI_ Static.generateSite Static.serveStaticFiles cfgPath logPath

apps/smp-server/static/contact/index.html

@@ -0,0 +1 @@
+../link.html

apps/smp-server/static/invitation/index.html

@@ -0,0 +1 @@
+../link.html

apps/smp-server/static/media/apple_store.svg

@@ -0,0 +1,26 @@
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apps/smp-server/static/media/contact.js

@@ -0,0 +1,66 @@
+(function () {
+
+  let complete = false
+  run()
+  window.onload = run
+
+  async function run() {
+    const connURIel = document.getElementById("conn_req_uri_text");
+    const mobileConnURIanchor = document.getElementById("mobile_conn_req_uri");
+    const connQRCodes = document.getElementsByClassName("conn_req_uri_qrcode");
+    console.log(connQRCodes);
+    if (complete || !connURIel || !mobileConnURIanchor || connQRCodes < 2) return
+    complete = true
+    let connURI = document.location.toString()
+    const parsedURI = new URL(connURI)
+    const path = parsedURI.pathname.split("/")
+    const len = path.length
+    const action = path[len - (path[len - 1] == "" ? 2 : 1)]
+    parsedURI.protocol = "https"
+    parsedURI.pathname = "/" + action
+    connURI = parsedURI.toString()
+    console.log("connection URI: ", connURI)
+    mobileConnURIanchor.href = "simplex:" + parsedURI.pathname + parsedURI.hash
+    connURIel.innerText = "/c " + connURI
+    for (const connQRCode of connQRCodes) {
+      try {
+        await QRCode.toCanvas(connQRCode, connURI, {
+          errorCorrectionLevel: "M",
+          color: {dark: "#062D56"}
+        });
+        connQRCode.style.width = "320px";
+        connQRCode.style.height = "320px";
+      } catch (err) {
+        console.error(err);
+      }
+    }
+
+    function contentCopyWithTooltip(parent) {
+      const content = parent.querySelector(".content");
+      const tooltip = parent.querySelector(".tooltiptext");
+      console.log(parent.querySelector(".content_copy"), 111)
+      console.log(parent)
+      const copyButton = parent.querySelector(".content_copy");
+      copyButton.addEventListener("click", copyAddress)
+      copyButton.addEventListener("mouseout", resetTooltip)
+
+      function copyAddress() {
+        navigator.clipboard.writeText(content.innerText || content.value);
+        tooltip.innerHTML = "Copied!";
+      }
+
+      function resetTooltip() {
+        tooltip.innerHTML = "Copy to clipboard";
+      }
+    }
+
+    function copyAddress() {
+      navigator.clipboard.writeText(connURI);
+      tooltipEl.innerHTML = "Copied!";
+    }
+
+    function resetTooltip() {
+      tooltipEl.innerHTML = "Copy to clipboard";
+    }
+  }
+})();

apps/smp-server/static/media/f_droid.svg

@@ -0,0 +1,372 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   width="560"
+   height="164"
+   version="1.1"
+   id="svg1048"
+   sodipodi:docname="f_droid.svg"
+   inkscape:version="1.1.2 (0a00cf5339, 2022-02-04, custom)"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:xlink="http://www.w3.org/1999/xlink"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <sodipodi:namedview
+     id="namedview1050"
+     pagecolor="#505050"
+     bordercolor="#ffffff"
+     borderopacity="1"
+     inkscape:pageshadow="0"
+     inkscape:pageopacity="0"
+     inkscape:pagecheckerboard="1"
+     showgrid="false"
+     inkscape:snap-bbox="true"
+     inkscape:bbox-paths="true"
+     inkscape:bbox-nodes="true"
+     inkscape:snap-bbox-edge-midpoints="true"
+     inkscape:snap-bbox-midpoints="true"
+     inkscape:snap-intersection-paths="true"
+     inkscape:object-paths="true"
+     inkscape:snap-smooth-nodes="true"
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+<path opacity="0.12" d="M10.4 32.8C10.1 32.5 10 32 10 31.4V31.5C10 32.1 10.2 32.6 10.5 32.9V32.8H10.4ZM32 21.8L27 24.6L27.1 24.7L32 21.9C32.7 21.5 33 21 33 20.5C33 21 32.6 21.4 32 21.8V21.8Z" fill="black"/>
+<path opacity="0.25" d="M12.5 8.10003L32 19.2C32.6 19.6 33 20 33 20.5C33 20 32.7 19.5 32 19.1L12.5 8.00003C11.1 7.20003 10 7.80003 10 9.40003V9.50003C10 8.00003 11.1 7.30003 12.5 8.10003Z" fill="white"/>
+<defs>
+<linearGradient id="paint0_linear_7_408" x1="21.8" y1="9.21" x2="5.017" y2="25.992" gradientUnits="userSpaceOnUse">
+<stop stop-color="#00A0FF"/>
+<stop offset="0.007" stop-color="#00A1FF"/>
+<stop offset="0.26" stop-color="#00BEFF"/>
+<stop offset="0.512" stop-color="#00D2FF"/>
+<stop offset="0.76" stop-color="#00DFFF"/>
+<stop offset="1" stop-color="#00E3FF"/>
+</linearGradient>
+<linearGradient id="paint1_linear_7_408" x1="33.834" y1="20.501" x2="9.63699" y2="20.501" gradientUnits="userSpaceOnUse">
+<stop stop-color="#FFE000"/>
+<stop offset="0.409" stop-color="#FFBD00"/>
+<stop offset="0.775" stop-color="#FFA500"/>
+<stop offset="1" stop-color="#FF9C00"/>
+</linearGradient>
+<linearGradient id="paint2_linear_7_408" x1="24.827" y1="22.796" x2="2.069" y2="45.554" gradientUnits="userSpaceOnUse">
+<stop stop-color="#FF3A44"/>
+<stop offset="1" stop-color="#C31162"/>
+</linearGradient>
+<linearGradient id="paint3_linear_7_408" x1="7.29699" y1="0.676051" x2="17.46" y2="10.8391" gradientUnits="userSpaceOnUse">
+<stop stop-color="#32A071"/>
+<stop offset="0.069" stop-color="#2DA771"/>
+<stop offset="0.476" stop-color="#15CF74"/>
+<stop offset="0.801" stop-color="#06E775"/>
+<stop offset="1" stop-color="#00F076"/>
+</linearGradient>
+</defs>
+</svg>

apps/smp-server/static/media/logo-symbol-dark.svg

@@ -0,0 +1,10 @@
+<svg width="34" height="35" viewBox="0 0 34 35" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path fill-rule="evenodd" clip-rule="evenodd" d="M3.02958 8.60922L8.622 14.2013L14.3705 8.45375L17.1669 11.2498L11.4183 16.9972L17.0114 22.5895L14.1373 25.4633L8.54422 19.871L2.79636 25.6187L0 22.8227L5.74794 17.075L0.155484 11.483L3.02958 8.60922Z" fill="white"/>
+<path fill-rule="evenodd" clip-rule="evenodd" d="M14.0923 25.5156L16.944 22.6642L16.9429 22.6634L22.6467 16.9612L17.0513 11.3675L17.0523 11.367L14.2548 8.56979L8.65972 2.97535L11.5114 0.123963L17.1061 5.71849L22.8099 0.015625L25.6074 2.81285L19.9035 8.51562L25.4984 14.1099L31.2025 8.40729L34 11.2045L28.2958 16.907L33.8917 22.5017L31.0399 25.3531L25.4442 19.7584L19.7409 25.4611L25.3365 31.0559L22.4848 33.9073L16.8892 28.3124L11.1864 34.0156L8.38885 31.2184L14.0923 25.5156Z" fill="url(#paint0_linear_656_10815)"/>
+<defs>
+<linearGradient id="paint0_linear_656_10815" x1="12.8381" y1="-0.678252" x2="9.54355" y2="31.4493" gradientUnits="userSpaceOnUse">
+<stop stop-color="#01F1FF"/>
+<stop offset="1" stop-color="#0197FF"/>
+</linearGradient>
+</defs>
+</svg>

apps/smp-server/static/media/logo-symbol-light.svg

@@ -0,0 +1,15 @@
+<svg width="34" height="34" viewBox="0 0 34 34" fill="none" xmlns="http://www.w3.org/2000/svg">
+<g clip-path="url(#clip0_14_10)">
+<path fill-rule="evenodd" clip-rule="evenodd" d="M3.02972 8.59396L8.62219 14.186L14.3703 8.43848L17.1668 11.2346L11.4182 16.982L17.0112 22.5742L14.1371 25.448L8.5441 19.8557L2.79651 25.6035L0 22.8074L5.74813 17.0597L0.155656 11.4678L3.02972 8.59396Z" fill="#023789"/>
+<path fill-rule="evenodd" clip-rule="evenodd" d="M14.0922 25.5L16.9434 22.6486L16.9423 22.6478L22.6464 16.9456L17.0512 11.3519L17.0518 11.3514L14.2542 8.55418L8.65961 2.95973L11.5114 0.108337L17.106 5.70288L22.8095 0L25.607 2.79722L19.903 8.5L25.4981 14.0943L31.2022 8.39169L33.9997 11.1889L28.2957 16.8914L33.8914 22.4861L31.0396 25.3375L25.4439 19.7428L19.7404 25.4454L25.3361 31.0403L22.4843 33.8917L16.8887 28.2968L11.1862 34L8.38867 31.2028L14.0922 25.5Z" fill="url(#paint0_linear_14_10)"/>
+</g>
+<defs>
+<linearGradient id="paint0_linear_14_10" x1="12.8379" y1="-0.693875" x2="9.54344" y2="31.4337" gradientUnits="userSpaceOnUse">
+<stop stop-color="#01F1FF"/>
+<stop offset="1" stop-color="#0197FF"/>
+</linearGradient>
+<clipPath id="clip0_14_10">
+<rect width="34" height="34" fill="white"/>
+</clipPath>
+</defs>
+</svg>

apps/smp-server/static/media/moon.svg

@@ -0,0 +1,3 @@
+<svg width="16" height="16" viewBox="0 0 16 16" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M2.92814 12.6789C6.17655 15.9347 11.7044 15.6463 14.5425 12.0117C14.6636 11.8566 14.6825 11.6448 14.5907 11.4708C14.4989 11.2967 14.3136 11.1926 14.1172 11.2049C11.5269 11.3673 8.97627 10.4315 7.0743 8.52765C5.17264 6.62414 4.23958 4.06868 4.40169 1.47281C4.41397 1.2762 4.30965 1.09069 4.13526 0.999048C3.96088 0.907402 3.74893 0.926696 3.59396 1.04833C3.36099 1.23117 3.13828 1.42685 2.92823 1.63726C-0.111372 4.68223 -0.111585 9.63533 2.92814 12.6789Z" stroke="black" stroke-miterlimit="10" stroke-linejoin="round"/>
+</svg>

apps/smp-server/static/media/script.js

@@ -0,0 +1,39 @@
+const isMobile = {
+    Android: () => navigator.userAgent.match(/Android/i),
+    iOS: () => navigator.userAgent.match(/iPhone|iPad|iPod/i)
+};
+
+window.addEventListener('click', clickHandler)
+
+if (isMobile.iOS) {
+    for (const btn of document.getElementsByClassName("close-overlay-btn")) {
+        btn.addEventListener("touchend", (e) => setTimeout(() => closeOverlay(e), 100))
+    }
+}
+
+function clickHandler(e) {
+    if (e.target.closest('.contact-tab-btn')) {
+        e.target.closest('.contact-tab').classList.toggle('active')
+    }
+}
+
+window.addEventListener('load', () => {
+    const googlePlayBtn = document.querySelector('.google-play-btn');
+    const appleStoreBtn = document.querySelector('.apple-store-btn');
+    const fDroidBtn = document.querySelector('.f-droid-btn');
+    if (!googlePlayBtn || !appleStoreBtn || !fDroidBtn) return;
+
+
+    if (isMobile.Android()) {
+        googlePlayBtn.classList.remove('hidden');
+        fDroidBtn.classList.remove('hidden');
+    }
+    else if (isMobile.iOS()) {
+        appleStoreBtn.classList.remove('hidden');
+    }
+    else {
+        appleStoreBtn.classList.remove('hidden');
+        googlePlayBtn.classList.remove('hidden');
+        fDroidBtn.classList.remove('hidden');
+    }
+})

apps/smp-server/static/media/style.css

@@ -0,0 +1,414 @@
+@font-face {
+  font-family: Gilroy;
+  src: url("GilroyRegular.woff2") format("woff2");
+  font-weight: 400;
+  font-style: normal;
+}
+
+@font-face {
+  font-family: Gilroy;
+  src: url("GilroyLight.woff2") format("woff2");
+  font-weight: 300;
+  font-style: normal;
+}
+
+@font-face {
+  font-family: Gilroy;
+  src: url("GilroyMedium.woff2") format("woff2");
+  font-weight: 500;
+  font-style: normal;
+}
+
+@font-face {
+  font-family: Gilroy;
+  src: url("GilroyBold.woff2") format("woff2");
+  font-weight: 700;
+  font-style: normal;
+}
+
+@font-face {
+  font-family: Gilroy;
+  src: url("GilroyRegularItalic.woff2") format("woff2");
+  font-weight: 400;
+  font-style: italic;
+}
+
+html {
+  scroll-behavior: smooth;
+  font-family: Gilroy, Helvetica, sans-serif;
+  ;
+  letter-spacing: 0.003em;
+}
+
+img {
+  user-select: none;
+  -webkit-user-select: none;
+  /* For Safari and older Chrome versions */
+  -moz-user-select: none;
+  /* For Firefox */
+  -ms-user-select: none;
+  /* For Internet Explorer and Edge */
+}
+
+a{
+  word-wrap: break-word;
+}
+
+/* NEW SITE */
+.container,
+.container-fluid,
+.container-xxl,
+.container-xl,
+.container-lg,
+.container-md,
+.container-sm {
+  width: 100%;
+  /* padding: 0 20px; */
+  margin-right: auto;
+  margin-left: auto;
+}
+
+@media (min-width: 576px) {
+
+  .container-sm,
+  .container {
+    max-width: 540px;
+  }
+}
+
+@media (min-width: 768px) {
+
+  .container-md,
+  .container-sm,
+  .container {
+    max-width: 720px;
+  }
+}
+
+@media (min-width: 992px) {
+
+  .container-lg,
+  .container-md,
+  .container-sm,
+  .container {
+    max-width: 960px;
+  }
+}
+
+@media (min-width: 1200px) {
+
+  .container-xl,
+  .container-lg,
+  .container-md,
+  .container-sm,
+  .container {
+    max-width: 1140px;
+  }
+}
+
+@media (min-width: 1400px) {
+
+  .container-xxl,
+  .container-xl,
+  .container-lg,
+  .container-md,
+  .container-sm,
+  .container {
+    max-width: 1320px;
+  }
+}
+
+.gradient-text {
+  background: -webkit-linear-gradient(to bottom, #53C1FF -50%, #0053D0 160%);
+  background: linear-gradient(to bottom, #53C1FF -50%, #0053D0 160%);
+  -webkit-background-clip: text;
+  -webkit-text-fill-color: transparent;
+  background-clip: text;
+  text-fill-color: transparent;
+}
+
+.dark .border-gradient {
+  background:
+    linear-gradient(#11182F, #11182F) padding-box,
+    linear-gradient(to bottom, transparent, #01F1FF 58%) border-box;
+  border: 1px solid transparent;
+}
+
+.dark .only-light {
+  display: none;
+}
+
+.only-dark {
+  display: none;
+}
+
+.dark .only-dark {
+  display: inherit;
+}
+
+.menu-link {
+  font-size: 16px;
+  line-height: 33.42px;
+  color: #0D0E12;
+}
+
+.dark .menu-link {
+  color: #fff;
+}
+
+.nav-link ul li a.active {
+  color: #0053D0;
+
+}
+
+.dark .nav-link ul li a.active {
+  color: #66D9E2;
+}
+
+@media (min-width:1024px) {
+
+  .nav-link-text,
+  .menu-link {
+    display: inline-block;
+    position: relative;
+    color: #0D0E12;
+  }
+
+  .nav-link-text::before,
+  .active .nav-link-text::before,
+  .menu-link::before {
+    content: "";
+    position: absolute;
+    width: 0;
+    height: 1px;
+    bottom: 0;
+    right: 0;
+    /* background-color: initial; */
+    transition: width 0.25s ease-out;
+  }
+
+  .menu-link::before {
+    background-color: #0D0E12;
+  }
+
+  .dark .menu-link::before {
+    background-color: #fff;
+  }
+
+  .active .nav-link-text::before {
+    width: 100%;
+  }
+
+  .nav-link:hover .nav-link-text::before,
+  .menu-link:hover::before {
+    width: 100%;
+    left: 0;
+    right: auto;
+  }
+}
+
+
+.sub-menu {
+  visibility: hidden;
+  opacity: 0;
+  color: #505158;
+}
+
+.sub-menu .no-hover {
+  color: #505158 !important;
+}
+
+.dark .sub-menu,
+.dark .sub-menu .no-hover {
+  color: #fff !important;
+}
+
+.dark .sub-menu li:hover {
+  color: #66D9E2;
+}
+
+.sub-menu li:hover {
+  color: #0053D0;
+}
+
+.sub-menu {
+  transition: all .3s ease !important;
+}
+
+.nav-link span svg,
+header nav {
+  transition: all 0.5s ease;
+}
+
+.nav-link:hover span svg {
+  transform: rotate(180deg);
+}
+
+@media (min-width:1024px) {
+
+  .nav-link:hover .sub-menu,
+  .nav-link:focus-within .sub-menu {
+    visibility: visible;
+    opacity: 1;
+    margin-top: 0;
+  }
+}
+
+@media (max-width: 1024px) {
+  .sub-menu {
+    max-height: 0;
+    transform: translateY(-10px);
+    transition: all .7s ease !important;
+  }
+
+  .active .sub-menu {
+    max-height: 600px;
+    transform: translateY(0px);
+    opacity: 1;
+    visibility: visible;
+    margin-top: 0;
+  }
+
+  header nav {
+    visibility: hidden;
+    opacity: 0;
+    transform: translateX(100%);
+  }
+
+  header nav.open {
+    visibility: visible;
+    opacity: 1;
+    transform: translateX(0);
+  }
+}
+
+.lock-scroll {
+  overflow: hidden;
+}
+
+/* hero */
+header {
+  transition: all .7s ease;
+}
+
+.primary-header {
+  background: linear-gradient(270deg, #0053D0 35.85%, #0197FF 94.78%);
+  -webkit-background-clip: text;
+  -webkit-text-fill-color: transparent;
+  background-clip: text;
+  text-shadow: 0px 4px 74px #e9e7e2;
+}
+
+.dark .primary-header {
+  background: linear-gradient(270deg, #70F0F9 100%, #70F0F9 100%);
+  -webkit-background-clip: text;
+  -webkit-text-fill-color: transparent;
+  background-clip: text;
+  text-shadow: none;
+}
+
+.secondary-header {
+  color: #606c71;
+  text-shadow: 0px 4px 74px #e9e7e2;
+}
+
+.dark .secondary-header {
+  color: #fff;
+  text-shadow: none;
+}
+
+.description {
+  width: 31rem;
+}
+
+p a {
+  color: #0053D0;
+  text-decoration: underline;
+  text-underline-offset: 2px;
+}
+
+.dark p a {
+  color: #70F0F9;
+}
+
+/* For Contact & Invitation Page */
+.primary-header-contact {
+  background: linear-gradient(251.16deg, #53c1ff 1.1%, #0053d0 100.82%);
+  -webkit-background-clip: text;
+  -webkit-text-fill-color: transparent;
+  background-clip: text;
+  text-shadow: 0px 4px 74px #e9e7e2;
+}
+
+.dark .primary-header-contact {
+  background: linear-gradient(270deg, #70F0F9 100%, #70F0F9 100%);
+  -webkit-background-clip: text;
+  -webkit-text-fill-color: transparent;
+  background-clip: text;
+  text-shadow: none;
+}
+
+.secondary-header-contact {
+  text-shadow: 0px 4px 74px #e9e7e2;
+}
+
+.dark .secondary-header-contact {
+  text-shadow: none;
+}
+
+.content_copy_with_tooltip {
+  background-color: #f8f8f6;
+  border-radius: 50px;
+  padding-bottom: 4px;
+  padding-top: 8px;
+  margin-top: 16px;
+  margin-bottom: 16px;
+}
+
+.content_copy_with_tooltip .tooltip {
+  vertical-align: -6px;
+}
+
+.content_copy_with_tooltip .content {
+  font-size: 15px;
+}
+
+.contact-tab>.contact-tab-content,
+.job-tab>.job-tab-content {
+  opacity: 0;
+  max-height: 0;
+  transition: all 0.5s ease;
+  visibility: hidden;
+  transform: translateY(10px);
+  overflow: hidden;
+}
+
+.contact-tab svg,
+.job-tab svg {
+  transform: rotate(-180deg);
+  transition: all .5s ease;
+}
+
+.contact-tab.active>.contact-tab-content,
+.job-tab.active>.job-tab-content {
+  opacity: 1;
+  max-height: 300px;
+  visibility: visible;
+  transform: translateY(0px);
+}
+
+.for-tablet .contact-tab.active>.contact-tab-content,
+.for-tablet .job-tab.active>.job-tab-content {
+  min-height: 450px;
+}
+
+.contact-tab.active svg,
+.contact-tab:hover svg,
+.job-tab.active svg,
+.job-tab:hover svg {
+  transform: rotate(0deg);
+}
+
+.d-none-if-js-disabled {
+  display: none !important;
+}

apps/smp-server/static/media/sun.svg

@@ -0,0 +1,11 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M23.9958 12.2815C23.9363 12.3954 23.8849 12.5146 23.8158 12.6224C23.5945 12.9674 23.2766 13.1624 22.8654 13.1685C22.2182 13.1782 21.5707 13.1764 20.9234 13.17C20.2781 13.1636 19.7772 12.6464 19.7773 11.9999C19.7774 11.3535 20.2754 10.8389 20.9237 10.8303C21.532 10.8221 22.1405 10.8258 22.7488 10.8278C23.3522 10.8298 23.7281 11.0908 23.9462 11.6508C23.956 11.6761 23.9789 11.6964 23.9958 11.719C23.9958 11.9064 23.9958 12.094 23.9958 12.2815Z" fill="white"/>
+<path d="M11.7154 24.0003C11.6217 23.9526 11.5256 23.9088 11.4345 23.8564C11.0545 23.6377 10.836 23.3104 10.8286 22.87C10.8175 22.2149 10.8179 21.5593 10.828 20.9042C10.8378 20.2738 11.3597 19.7812 11.9967 19.7812C12.6336 19.7812 13.155 20.2739 13.1654 20.9042C13.1757 21.5359 13.1717 22.168 13.1682 22.7998C13.1652 23.3392 12.8885 23.7369 12.3906 23.937C12.3509 23.9529 12.3153 23.979 12.2779 24.0003C12.0904 24.0003 11.9029 24.0003 11.7154 24.0003Z" fill="white"/>
+<path d="M17.2592 11.9958C17.2733 14.8825 14.9232 17.2468 12.0032 17.2612C9.11732 17.2754 6.75397 14.9264 6.73836 12.0041C6.72295 9.12027 9.07502 6.75326 11.9946 6.73835C14.8788 6.72363 17.2449 9.07587 17.2592 11.9958Z" stroke="white" stroke-width="1.5"/>
+<path d="M13.1693 2.11324C13.1692 2.43329 13.1744 2.75345 13.1682 3.07341C13.1555 3.7216 12.6425 4.21934 11.995 4.21864C11.3493 4.21789 10.8358 3.71808 10.828 3.06768C10.8204 2.42766 10.8201 1.78736 10.8283 1.14738C10.8365 0.500704 11.3562 -0.000843934 12.0007 1.06615e-06C12.6437 0.000846066 13.1564 0.504314 13.1684 1.15307C13.1743 1.47303 13.1694 1.79318 13.1693 2.11324Z" fill="white"/>
+<path d="M2.10878 13.1714C1.78877 13.1714 1.46872 13.1754 1.14885 13.1705C0.504832 13.1605 -0.000422735 12.6426 2.65407e-07 11.9987C0.000423265 11.3553 0.503376 10.838 1.15138 10.8301C1.79126 10.8223 2.43138 10.8222 3.07126 10.8303C3.72034 10.8385 4.21822 11.3541 4.21794 12.0012C4.21766 12.6477 3.71555 13.1609 3.06872 13.1706C2.7488 13.1753 2.42875 13.1714 2.10878 13.1714Z" fill="white"/>
+<path d="M6.85268 5.524C6.82732 6.152 6.60944 6.52005 6.16969 6.72981C5.73844 6.93552 5.29738 6.90378 4.94534 6.58208C4.41604 6.09838 3.90431 5.59148 3.42451 5.05894C3.02923 4.62023 3.09727 3.9209 3.51626 3.50792C3.9361 3.09409 4.63284 3.03567 5.06893 3.43194C5.59381 3.90888 6.09569 4.41446 6.57188 4.93996C6.73726 5.12252 6.79642 5.4014 6.85268 5.524Z" fill="white"/>
+<path d="M17.1426 18.4446C17.1749 17.8424 17.389 17.4819 17.8198 17.2738C18.2418 17.07 18.6812 17.0888 19.0265 17.3998C19.5706 17.8899 20.0919 18.4099 20.5814 18.9544C20.9675 19.384 20.895 20.0764 20.485 20.4873C20.0824 20.8907 19.3961 20.9756 18.9718 20.5988C18.4129 20.1026 17.89 19.5625 17.3864 19.0096C17.2323 18.8405 17.1926 18.5671 17.1426 18.4446Z" fill="white"/>
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+<path d="M5.54205 17.1445C6.14812 17.1747 6.51058 17.385 6.72137 17.8153C6.9323 18.2459 6.90765 18.6892 6.58942 19.0415C6.1037 19.5791 5.58933 20.0948 5.05088 20.5795C4.62165 20.9659 3.93035 20.8989 3.51681 20.4933C3.09875 20.0833 3.02864 19.3789 3.4227 18.942C3.908 18.404 4.42706 17.8934 4.96382 17.4066C5.13982 17.247 5.41663 17.1985 5.54205 17.1445Z" fill="white"/>
+</svg>

apps/smp-server/web/Static.hs

@@ -0,0 +1,176 @@
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Static where
+
+import Control.Logger.Simple
+import Control.Monad
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as B
+import Data.Maybe (fromMaybe)
+import Data.String (fromString)
+import Data.Text.Encoding (encodeUtf8)
+import Network.Wai.Application.Static as S
+import Network.Wai.Handler.Warp as W
+import qualified Network.Wai.Handler.WarpTLS as W
+import Simplex.Messaging.Encoding.String (strEncode)
+import Simplex.Messaging.Server.Information
+import Simplex.Messaging.Server.Main (EmbeddedWebParams (..), WebHttpsParams (..))
+import Simplex.Messaging.Transport.Client (TransportHost (..))
+import Simplex.Messaging.Util (tshow)
+import Static.Embedded as E
+import System.Directory (createDirectoryIfMissing)
+import System.FilePath
+import UnliftIO.Concurrent (forkFinally)
+
+serveStaticFiles :: EmbeddedWebParams -> IO ()
+serveStaticFiles EmbeddedWebParams {webStaticPath, webHttpPort, webHttpsParams} = do
+  forM_ webHttpPort $ \port -> flip forkFinally (\e -> logError $ "HTTP server crashed: " <> tshow e) $ do
+    logInfo $ "Serving static site on port " <> tshow port
+    W.runSettings (mkSettings port) (S.staticApp $ S.defaultFileServerSettings webStaticPath)
+  forM_ webHttpsParams $ \WebHttpsParams {port, cert, key} -> flip forkFinally (\e -> logError $ "HTTPS server crashed: " <> tshow e) $ do
+    logInfo $ "Serving static site on port " <> tshow port <> " (TLS)"
+    W.runTLS (W.tlsSettings cert key) (mkSettings port) (S.staticApp $ S.defaultFileServerSettings webStaticPath)
+  where
+    mkSettings port = setPort port defaultSettings
+
+generateSite :: ServerInformation -> Maybe TransportHost -> FilePath -> IO ()
+generateSite si onionHost sitePath = do
+  createDirectoryIfMissing True sitePath
+  B.writeFile (sitePath </> "index.html") $ serverInformation si onionHost
+  createDirectoryIfMissing True $ sitePath </> "media"
+  forM_ E.mediaContent $ \(path, bs) -> B.writeFile (sitePath </> "media" </> path) bs
+  createDirectoryIfMissing True $ sitePath </> "contact"
+  B.writeFile (sitePath </> "contact" </> "index.html") E.linkHtml
+  createDirectoryIfMissing True $ sitePath </> "invitation"
+  B.writeFile (sitePath </> "invitation" </> "index.html") E.linkHtml
+  logInfo $ "Generated static site contents at " <> tshow sitePath
+
+serverInformation :: ServerInformation -> Maybe TransportHost -> ByteString
+serverInformation ServerInformation {config, information} onionHost = render E.indexHtml substs
+  where
+    substs = substConfig <> maybe [] substInfo information <> [("onionHost", strEncode <$> onionHost)]
+    substConfig =
+      [ ( "persistence",
+          Just $ case persistence config of
+            SPMMemoryOnly -> "In-memory only"
+            SPMQueues -> "Queues"
+            SPMMessages -> "Queues and messages"
+        ),
+        ("messageExpiration", Just $ maybe "Never" (fromString . timedTTLText) $ messageExpiration config),
+        ("statsEnabled", Just . yesNo $ statsEnabled config),
+        ("newQueuesAllowed", Just . yesNo $ newQueuesAllowed config),
+        ("basicAuthEnabled", Just . yesNo $ basicAuthEnabled config)
+      ]
+    yesNo True = "Yes"
+    yesNo False = "No"
+    substInfo spi =
+      concat
+        [ basic,
+          maybe [("usageConditions", Nothing), ("usageAmendments", Nothing)] conds (usageConditions spi),
+          maybe [("operator", Nothing)] operatorE (operator spi),
+          maybe [("admin", Nothing)] admin (adminContacts spi),
+          maybe [("complaints", Nothing)] complaints (complaintsContacts spi),
+          maybe [("hosting", Nothing)] hostingE (hosting spi),
+          server
+        ]
+      where
+        basic =
+          [ ("sourceCode", Just . encodeUtf8 $ sourceCode spi),
+            ("website", encodeUtf8 <$> website spi)
+          ]
+        conds ServerConditions {conditions, amendments} =
+          [ ("usageConditions", Just $ encodeUtf8 conditions),
+            ("usageAmendments", encodeUtf8 <$> amendments)
+          ]
+        operatorE Entity {name, country} =
+          [ ("operator", Just ""),
+            ("operatorEntity", Just $ encodeUtf8 name),
+            ("operatorCountry", encodeUtf8 <$> country)
+          ]
+        admin ServerContactAddress {simplex, email, pgp} =
+          [ ("admin", Just ""),
+            ("adminSimplex", strEncode <$> simplex),
+            ("adminEmail", encodeUtf8 <$> email),
+            ("adminPGP", encodeUtf8 . pkURI <$> pgp),
+            ("adminPGPFingerprint", encodeUtf8 . pkFingerprint <$> pgp)
+          ]
+        complaints ServerContactAddress {simplex, email, pgp} =
+          [ ("complaints", Just ""),
+            ("complaintsSimplex", strEncode <$> simplex),
+            ("complaintsEmail", encodeUtf8 <$> email),
+            ("complaintsPGP", encodeUtf8 . pkURI <$> pgp),
+            ("complaintsPGPFingerprint", encodeUtf8 . pkFingerprint <$> pgp)
+          ]
+        hostingE Entity {name, country} =
+          [ ("hosting", Just ""),
+            ("hostingEntity", Just $ encodeUtf8 name),
+            ("hostingCountry", encodeUtf8 <$> country)
+          ]
+        server =
+          [ ("serverCountry", fmap encodeUtf8 $ serverCountry =<< information)
+          ]
+
+-- Copy-pasted from simplex-chat Simplex.Chat.Types.Preferences
+{-# INLINE timedTTLText #-}
+timedTTLText :: (Integral i, Show i) => i -> String
+timedTTLText 0 = "0 sec"
+timedTTLText ttl = do
+  let (m', s) = ttl `quotRem` 60
+      (h', m) = m' `quotRem` 60
+      (d', h) = h' `quotRem` 24
+      (mm, d) = d' `quotRem` 30
+  unwords $
+    [mms mm | mm /= 0]
+      <> [ds d | d /= 0]
+      <> [hs h | h /= 0]
+      <> [ms m | m /= 0]
+      <> [ss s | s /= 0]
+  where
+    ss s = show s <> " sec"
+    ms m = show m <> " min"
+    hs 1 = "1 hour"
+    hs h = show h <> " hours"
+    ds 1 = "1 day"
+    ds 7 = "1 week"
+    ds 14 = "2 weeks"
+    ds d = show d <> " days"
+    mms 1 = "1 month"
+    mms mm = show mm <> " months"
+
+-- | Rewrite source with provided substitutions
+render :: ByteString -> [(ByteString, Maybe ByteString)] -> ByteString
+render src = \case
+  [] -> src
+  (label, content') : rest -> render (section_ label content' src) rest
+
+-- | Rewrite section content inside @<x-label>...</x-label>@ markers.
+-- Markers are always removed when found. Closing marker is mandatory.
+-- If content is absent, whole section is removed.
+-- Section content is delegated to `item_`. If no sections found, the whole source is delegated.
+section_ :: ByteString -> Maybe ByteString -> ByteString -> ByteString
+section_ label content' src =
+  case B.breakSubstring startMarker src of
+    (_, "") -> item_ label (fromMaybe "" content') src -- no section, just replace items
+    (before, afterStart') ->
+      -- found section start, search for end too
+      case B.breakSubstring endMarker $ B.drop (B.length startMarker) afterStart' of
+        (_, "") -> error $ "missing section end: " <> show endMarker
+        (inside, next') ->
+          let next = B.drop (B.length endMarker) next'
+           in case content' of
+                Nothing -> before <> next -- collapse section
+                Just content -> before <> item_ label content inside <> section_ label content' next
+  where
+    startMarker = "<x-" <> label <> ">"
+    endMarker = "</x-" <> label <> ">"
+
+-- | Replace all occurences of @${label}@ with provided content.
+item_ :: ByteString -> ByteString -> ByteString -> ByteString
+item_ label content' src =
+  case B.breakSubstring marker src of
+    (done, "") -> done
+    (before, after') -> before <> content' <> item_ label content' (B.drop (B.length marker) after')
+  where
+    marker = "${" <> label <> "}"

apps/smp-server/web/Static/Embedded.hs

@@ -0,0 +1,15 @@
+{-# LANGUAGE TemplateHaskell #-}
+
+module Static.Embedded where
+
+import Data.FileEmbed (embedDir, embedFile)
+import Data.ByteString (ByteString)
+
+indexHtml :: ByteString
+indexHtml = $(embedFile "apps/smp-server/static/index.html")
+
+linkHtml :: ByteString
+linkHtml = $(embedFile "apps/smp-server/static/link.html")
+
+mediaContent :: [(FilePath, ByteString)]
+mediaContent = $(embedDir "apps/smp-server/static/media/")

apps/xftp-server/Main.hs

@@ -0,0 +1,21 @@
+module Main where
+
+import Control.Logger.Simple
+import Simplex.Messaging.Server.CLI (getEnvPath)
+import Simplex.FileTransfer.Server.Main
+
+defaultCfgPath :: FilePath
+defaultCfgPath = "/etc/opt/simplex-xftp"
+
+defaultLogPath :: FilePath
+defaultLogPath = "/var/opt/simplex-xftp"
+
+logCfg :: LogConfig
+logCfg = LogConfig {lc_file = Nothing, lc_stderr = True}
+
+main :: IO ()
+main = do
+  setLogLevel LogDebug -- change to LogError in production
+  cfgPath <- getEnvPath "XFTP_SERVER_CFG_PATH" defaultCfgPath
+  logPath <- getEnvPath "XFTP_SERVER_LOG_PATH" defaultLogPath
+  withGlobalLogging logCfg $ xftpServerCLI cfgPath logPath

apps/xftp/Main.hs

@@ -0,0 +1,6 @@
+module Main where
+
+import Simplex.FileTransfer.Client.Main
+
+main :: IO ()
+main = xftpClientCLI

cabal.project

@@ -1,17 +1,30 @@
 packages: .
 -- packages: . ../direct-sqlcipher ../sqlcipher-simple
+-- packages: . ../hs-socks
+-- packages: . ../http2
+-- packages: . ../network-transport
+
+index-state: 2023-12-12T00:00:00Z
+
+package cryptostore
+    flags: +use_crypton
 
 source-repository-package
     type: git
     location: https://github.com/simplex-chat/aeson.git
-    tag: 3eb66f9a68f103b5f1489382aad89f5712a64db7
+    tag: aab7b5a14d6c5ea64c64dcaee418de1bb00dcc2b
+
+source-repository-package
+    type: git
+    location: https://github.com/simplex-chat/hs-socks.git
+    tag: a30cc7a79a08d8108316094f8f2f82a0c5e1ac51
 
 source-repository-package
     type: git
     location: https://github.com/simplex-chat/direct-sqlcipher.git
-    tag: 34309410eb2069b029b8fc1872deb1e0db123294
+    tag: f814ee68b16a9447fbb467ccc8f29bdd3546bfd9
 
 source-repository-package
     type: git
     location: https://github.com/simplex-chat/sqlcipher-simple.git
-    tag: 5e154a2aeccc33ead6c243ec07195ab673137221
+    tag: a46bd361a19376c5211f1058908fc0ae6bf42446

cbits/README.md

@@ -0,0 +1,3 @@
+# Streamlined NTRU Prime: sntrup761
+
+The implementation of sntrup761 is the _exact_ copy from this [Internet draft](https://www.ietf.org/archive/id/draft-josefsson-ntruprime-streamlined-00.html).

cbits/sha512.c

@@ -0,0 +1,9 @@
+#include <openssl/sha.h>
+#include "sha512.h"
+
+void crypto_hash_sha512 (unsigned char *out,
+                         const unsigned char *in,
+                         unsigned long long inlen)
+{
+  SHA512(in, inlen, out);
+}

cbits/sha512.h

@@ -0,0 +1,3 @@
+void crypto_hash_sha512 (unsigned char *out,
+                         const unsigned char *in,
+                         unsigned long long inlen);

cbits/sntrup761.h

@@ -0,0 +1,33 @@
+/*
+ * Derived from public domain source, written by (in alphabetical order):
+ * - Daniel J. Bernstein
+ * - Chitchanok Chuengsatiansup
+ * - Tanja Lange
+ * - Christine van Vredendaal
+ */
+
+#ifndef SNTRUP761_H
+#define SNTRUP761_H
+
+#include <string.h>
+#include <stdint.h>
+
+#define SNTRUP761_SECRETKEY_SIZE 1763
+#define SNTRUP761_PUBLICKEY_SIZE 1158
+#define SNTRUP761_CIPHERTEXT_SIZE 1039
+#define SNTRUP761_SIZE 32
+
+typedef void sntrup761_random_func (void *ctx, size_t length, uint8_t *dst);
+
+void
+sntrup761_keypair (uint8_t *pk, uint8_t *sk,
+                   void *random_ctx, sntrup761_random_func *random);
+
+void
+sntrup761_enc (uint8_t *c, uint8_t *k, const uint8_t *pk,
+               void *random_ctx, sntrup761_random_func *random);
+
+void
+sntrup761_dec (uint8_t *k, const uint8_t *c, const uint8_t *sk);
+
+#endif /* SNTRUP761_H */

fourmolu.yaml

@@ -0,0 +1,30 @@
+indentation: 2
+column-limit: none
+function-arrows: trailing
+comma-style: trailing
+import-export-style: trailing
+indent-wheres: true
+record-brace-space: true
+newlines-between-decls: 1
+haddock-style: single-line
+haddock-style-module: null
+let-style: inline
+in-style: right-align
+single-constraint-parens: never
+unicode: never
+respectful: true
+fixities:
+  - infixr 9 .
+  - infixr 8 .:, .:., .=
+  - infixr 6 <>
+  - infixr 5 ++
+  - infixl 4 <$>, <$, $>,  <$$>, <$?>
+  - infixl 4 <*>, <*, *>, <**>
+  - infix 4 ==, /=
+  - infixr 3 &&
+  - infixl 3 <|>
+  - infixr 2 ||
+  - infixl 1 >>, >>=
+  - infixr 1 =<<, >=>, <=<
+  - infixr 0 $, $!
+reexports: []

install.sh

@@ -0,0 +1,218 @@
+#!/usr/bin/env sh
+set -eu
+
+# Links to scripts/configs
+bin="https://github.com/simplex-chat/simplexmq/releases/latest/download"
+remote_version="$(curl --proto '=https' --tlsv1.2 -sSf -L https://api.github.com/repos/simplex-chat/simplexmq/releases/latest | grep -i "tag_name" | awk -F \" '{print $4}')"
+
+scripts="https://raw.githubusercontent.com/simplex-chat/simplexmq/stable/scripts/main"
+scripts_systemd_smp="$scripts/smp-server.service"
+scripts_systemd_xftp="$scripts/xftp-server.service"
+scripts_update="$scripts/simplex-servers-update"
+scripts_uninstall="$scripts/simplex-servers-uninstall"
+scripts_stopscript="$scripts/simplex-servers-stopscript"
+
+# Default installation paths
+path_bin="/usr/local/bin"
+path_bin_smp="$path_bin/smp-server"
+path_bin_xftp="$path_bin/xftp-server"
+path_bin_update="$path_bin/simplex-servers-update"
+path_bin_uninstall="$path_bin/simplex-servers-uninstall"
+path_bin_stopscript="$path_bin/simplex-servers-stopscript"
+
+path_conf_etc="/etc/opt"
+path_conf_var="/var/opt"
+path_conf_smp="$path_conf_etc/simplex $path_conf_var/simplex"
+path_conf_xftp="$path_conf_etc/simplex-xftp $path_conf_var/simplex-xftp /srv/xftp"
+
+path_conf_info="$path_conf_etc/simplex-info"
+
+path_systemd="/etc/systemd/system"
+path_systemd_smp="$path_systemd/smp-server.service"
+path_systemd_xftp="$path_systemd/xftp-server.service"
+
+# Defaut users
+user_smp="smp"
+user_xftp="xftp"
+
+GRN='\033[0;32m'
+BLU='\033[1;34m'
+YLW='\033[1;33m'
+RED='\033[0;31m'
+NC='\033[0m'
+
+logo='
+ ____  _                 _     __  __
+/ ___|(_)_ __ ___  _ __ | | ___\ \/ /
+\___ \| | '"'"'_ ` _ \| '"'"'_ \| |/ _ \\  / 
+ ___) | | | | | | | |_) | |  __//  \ 
+|____/|_|_| |_| |_| .__/|_|\___/_/\_\
+                  |_|                            
+'
+
+welcome="Welcome to SMP/XFTP installation script! Here's what we're going to do:
+${GRN}1.${NC} Install latest binaries from GitHub releases:
+    - smp: ${YLW}${path_bin_smp}${NC}
+    - xftp: ${YLW}${path_bin_xftp}${NC}
+${GRN}2.${NC} Create server directories:
+    - smp: ${YLW}${path_conf_smp}${NC}
+    - xftp: ${YLW}${path_conf_xftp}${NC}
+${GRN}3.${NC} Setup user for each server:
+    - xmp: ${YLW}${user_smp}${NC}
+    - xftp: ${YLW}${user_xftp}${NC}
+${GRN}4.${NC} Create systemd services:
+    - smp: ${YLW}${path_systemd_smp}${NC}
+    - xftp: ${YLW}${path_systemd_xftp}${NC}
+${GRN}5.${NC} Install stopscript (systemd), update and uninstallation script:
+    - all: ${YLW}${path_bin_update}${NC}, ${YLW}${path_bin_uninstall}${NC}, ${YLW}${path_bin_stopscript}${NC}
+
+Press:
+  - ${GRN}ENTER${NC} to continue installing both xftp and smp servers
+  - ${GRN}1${NC} to install only smp server
+  - ${GRN}2${NC} to install only xftp server
+  - ${RED}Ctrl+C${NC} to cancel installation
+  
+Selection: "
+
+end="Installtion is complete!
+
+Please checkout our server guides:
+- smp: ${GRN}https://simplex.chat/docs/server.html${NC}
+- xftp: ${GRN}https://simplex.chat/docs/xftp-server.html${NC}
+
+To uninstall with full clean-up, simply run: ${YLW}sudo /usr/local/bin/simplex-servers-uninstall${NC}
+"
+
+os_test() {
+ . /etc/os-release
+
+ case "$VERSION_ID" in
+  20.04|22.04) : ;;
+  24.04) VERSION_ID='22.04' ;;
+  *) printf "${RED}Unsupported Ubuntu version!${NC}\nPlease file Github issue with request to support Ubuntu %s: https://github.com/simplex-chat/simplexmq/issues/new\n" "$VERSION_ID" && exit 1 ;;
+ esac
+
+ version="$(printf '%s' "$VERSION_ID" | tr '.' '_')"
+ arch="$(uname -p)"
+
+ case "$arch" in
+  x86_64) arch="$(printf '%s' "$arch" | tr '_' '-')" ;;
+  *)  printf "${RED}Unsupported architecture!${NC}\nPlease file Github issue with request to support %s architecture: https://github.com/simplex-chat/simplexmq/issues/new" "$arch" && exit 1 ;;
+ esac
+
+ bin_smp="$bin/smp-server-ubuntu-${version}-${arch}"
+ bin_xftp="$bin/xftp-server-ubuntu-${version}-${arch}"
+}
+
+setup_bins() {
+ eval "bin=\$bin_${1}"
+ eval "path=\$path_bin_${1}"
+
+ curl --proto '=https' --tlsv1.2 -sSf -L "$bin" -o "$path" && chmod +x "$path"
+
+ unset bin path
+}
+
+setup_users() {
+ eval "user=\$user_${1}"
+
+ useradd -M "$user" 2> /dev/null || true
+
+ unset user
+}
+
+setup_dirs() {
+ # Unquoted varibles, so field splitting can occur
+ eval "path_conf=\$path_conf_${1}"
+ eval "user=\$user_${1}"
+
+ mkdir -p $path_conf
+ mkdir -p $path_conf_info
+ printf "local_version_%s='%s'\n" "$1" "$remote_version" >> "$path_conf_info/release"
+ chown -R "$user":"$user" $path_conf
+
+ unset path_conf user
+}
+
+setup_systemd() {
+ eval "scripts_systemd=\$scripts_systemd_${1}"
+ eval "path_systemd=\$path_systemd_${1}"
+
+ curl --proto '=https' --tlsv1.2 -sSf -L "$scripts_systemd" -o "$path_systemd"
+
+ unset scripts_systemd path_systemd
+}
+
+setup_scripts() {
+ curl --proto '=https' --tlsv1.2 -sSf -L "$scripts_update" -o "$path_bin_update" && chmod +x "$path_bin_update"
+ curl --proto '=https' --tlsv1.2 -sSf -L "$scripts_uninstall" -o "$path_bin_uninstall" && chmod +x "$path_bin_uninstall"
+ curl --proto '=https' --tlsv1.2 -sSf -L "$scripts_stopscript" -o "$path_bin_stopscript" && chmod +x "$path_bin_stopscript"
+ }
+
+checks() {
+ if [ "$(id -u)" -ne 0 ]; then
+  printf "This script is intended to be run with root privileges. Please re-run script using sudo."
+  exit 1
+ fi
+ 
+ os_test
+
+ mkdir -p $path_conf_info  
+}
+
+main() {
+ checks
+ 
+ printf "%b\n%b" "${BLU}$logo${NC}" "$welcome"
+ read ans
+
+ if [ "$ans" = '1' ]; then
+  setup='smp'
+ elif [ "$ans" = '2' ]; then
+  setup='xftp'
+ else
+  setup='smp xftp'
+ fi
+
+ printf "Installing binaries..."
+ 
+ for i in $setup; do
+  setup_bins "$i"
+ done
+ 
+ printf "${GRN} Done!${NC}\n"
+
+ printf "Creating users..."
+
+ for i in $setup; do
+  setup_users "$i"
+ done
+
+ printf "${GRN} Done!${NC}\n"
+ 
+ printf "Creating directories..."
+
+ for i in $setup; do
+  setup_dirs "$i"
+ done
+
+ printf "${GRN} Done!${NC}\n"
+
+ printf "Creating systemd services..."
+
+ for i in $setup; do
+  setup_systemd "$i"
+ done
+
+ printf "${GRN} Done!${NC}\n"
+
+ printf "Installing stopscript, update and uninstallation script..."
+
+ setup_scripts
+
+ printf "${GRN} Done!${NC}\n"
+
+ printf "%b" "$end"
+}
+
+main

notes-flow.txt

@@ -0,0 +1,23 @@
+common:
+  corrId - random BS, used as CbNonce
+  entityId - p2r tlsUniq
+
+# setup
+s->p: "proxy", uri, auth?
+  # unless connected
+  p->r: "p_handshake"
+  p<-r: "r_key", tls-signed dh pub
+s<-r: "r_key", tls-signed dh pub # reply entityId contains tlsUniq
+
+# working
+s ; generate random dh priv, make shared secret
+s->p: s2r("forward", random dh pub, SEND command blob)
+  p->r: p2r("forward", random dh pub, s2r("forward", ...)))
+    r->c@ "msg", ...
+  p<-r: p2r("r_res", s2r("ok" / "error", error))
+s<-p@ s2r("ok" / "error", error)
+
+# expired
+  p<-r@ p2r("error", "key expired")
+s<-p@ "error", "key expired"
+s ; reconnect

package.yaml

@@ -1,5 +1,5 @@
 name: simplexmq
-version: 3.4.0
+version: 6.0.4.0
 synopsis: SimpleXMQ message broker
 description: |
   This package includes <./docs/Simplex-Messaging-Server.html server>,
@@ -20,9 +20,13 @@ category: Chat, Network, Web, System, Cryptography
 extra-source-files:
   - README.md
   - CHANGELOG.md
+  - cbits/sha512.h
+  - cbits/sntrup761.h
+  - apps/smp-server/static/*.html
+  - apps/smp-server/static/media/*
 
 dependencies:
-  - aeson == 2.0.*
+  - aeson == 2.2.*
   - ansi-terminal >= 0.10 && < 0.12
   - asn1-encoding == 0.9.*
   - asn1-types == 0.3.*
@@ -30,70 +34,101 @@ dependencies:
   - attoparsec == 0.14.*
   - base >= 4.14 && < 5
   - base64-bytestring >= 1.0 && < 1.3
-  - bytestring == 0.10.*
   - case-insensitive == 1.2.*
   - composition == 1.0.*
   - constraints >= 0.12 && < 0.14
   - containers == 0.6.*
-  - cryptonite >= 0.27 && < 0.30
-  - cryptostore == 0.2.*
+  - crypton == 0.34.*
+  - crypton-x509 == 1.7.*
+  - crypton-x509-store == 1.6.*
+  - crypton-x509-validation == 1.6.*
+  - cryptostore == 0.3.*
   - data-default == 0.7.*
   - direct-sqlcipher == 2.3.*
   - directory == 1.3.*
   - filepath == 1.4.*
+  - hashable == 1.4.*
+  - hourglass == 0.2.*
   - http-types == 0.12.*
-  - http2 == 3.0.*
-  - generic-random >= 1.3 && < 1.5
+  - http2 >= 4.2.2 && < 4.3
   - ini == 0.4.1
+  - iproute == 1.7.*
   - iso8601-time == 0.1.*
-  - memory == 0.15.*
-  - mtl == 2.2.*
+  - memory == 0.18.*
+  - mtl >= 2.3.1 && < 3.0
   - network >= 3.1.2.7 && < 3.2
-  - network-transport == 0.5.4
+  - network-info >= 0.2 && < 0.3
+  - network-transport == 0.5.6
+  - network-udp >= 0.0 && < 0.1
   - optparse-applicative >= 0.15 && < 0.17
-  - QuickCheck == 2.14.*
   - process == 1.6.*
   - random >= 1.1 && < 1.3
   - simple-logger == 0.1.*
   - socks == 0.6.*
   - sqlcipher-simple == 0.4.*
   - stm == 2.5.*
-  - template-haskell == 2.16.*
-  - text == 1.2.*
-  - time == 1.9.*
-  - time-compat == 1.9.*
+  - temporary == 1.3.*
+  - time == 1.12.*
   - time-manager == 0.0.*
-  - tls >= 1.6.0 && < 1.7
-  - transformers == 0.5.*
+  - tls >= 1.9.0 && < 1.10
+  - transformers == 0.6.*
   - unliftio == 0.2.*
   - unliftio-core == 0.2.*
   - websockets == 0.12.*
-  - x509 == 1.7.*
-  - x509-store == 1.6.*
-  - x509-validation == 1.6.*
+  - yaml == 0.11.*
+  - zstd == 0.1.3.*
 
 flags:
   swift:
     description: Enable swift JSON format
     manual: True
     default: False
+  use_crypton:
+    description: Use crypton etc. in cryptostore
+    manual: True
+    default: True
+
+# cpp-options:
+#   - -Dslow_servers
 
 when:
   - condition: flag(swift)
     cpp-options:
       - -DswiftJSON
+  - condition: impl(ghc >= 9.6.2)
+    dependencies:
+      - bytestring == 0.11.*
+      - template-haskell == 2.20.*
+      - text >= 2.0.1 && < 2.2
+  - condition: impl(ghc < 9.6.2)
+    dependencies:
+      - bytestring == 0.10.*
+      - template-haskell == 2.16.*
+      - text >= 1.2.3.0 && < 1.3
 
 library:
   source-dirs: src
+  c-sources:
+    - cbits/sha512.c
+    - cbits/sntrup761.c
+  include-dirs: cbits
+  extra-libraries: crypto
 
 executables:
   smp-server:
-    source-dirs: apps/smp-server
+    source-dirs:
+    - apps/smp-server
+    - apps/smp-server/web
     main: Main.hs
     dependencies:
+      - file-embed
       - simplexmq
+      - wai-app-static
+      - warp
+      - warp-tls
     ghc-options:
       - -threaded
+      - -rtsopts
 
   ntf-server:
     source-dirs: apps/ntf-server
@@ -102,33 +137,76 @@ executables:
       - simplexmq
     ghc-options:
       - -threaded
+      - -rtsopts
 
-  smp-agent:
-    source-dirs: apps/smp-agent
+  xftp-server:
+    source-dirs: apps/xftp-server
     main: Main.hs
     dependencies:
       - simplexmq
     ghc-options:
       - -threaded
+      - -rtsopts
+
+  xftp:
+    source-dirs: apps/xftp
+    main: Main.hs
+    dependencies:
+      - simplexmq
+    ghc-options:
+      - -threaded
+      - -rtsopts
 
 tests:
-  smp-server-test:
+  simplexmq-test:
     source-dirs: tests
     main: Test.hs
     dependencies:
       - simplexmq
-      - hspec == 2.7.*
-      - hspec-core == 2.7.*
+      - deepseq == 1.4.*
+      - generic-random == 1.5.*
+      - hspec == 2.11.*
+      - hspec-core == 2.11.*
       - HUnit == 1.6.*
       - QuickCheck == 2.14.*
+      - silently == 1.2.*
+      - main-tester == 0.2.*
       - timeit == 2.0.*
+    ghc-options:
+      - -threaded
+      - -rtsopts
+      - -with-rtsopts=-A64M
+      - -with-rtsopts=-N1
 
 ghc-options:
   # - -haddock
-  - -Wall
+  - -Weverything
+  - -Wno-missing-exported-signatures
+  - -Wno-missing-import-lists
+  - -Wno-missed-specialisations
+  - -Wno-all-missed-specialisations
+  - -Wno-unsafe
+  - -Wno-safe
+  - -Wno-missing-local-signatures
+  - -Wno-missing-kind-signatures
+  - -Wno-missing-deriving-strategies
+  - -Wno-monomorphism-restriction
+  - -Wno-prepositive-qualified-module
+  - -Wno-unused-packages
+  - -Wno-implicit-prelude
+  - -Wno-missing-safe-haskell-mode
+  - -Wno-missing-export-lists
+  - -Wno-partial-fields
   - -Wcompat
+  - -Werror=incomplete-record-updates
   - -Werror=incomplete-patterns
+  - -Werror=incomplete-uni-patterns
+  - -Werror=missing-methods
+  - -Werror=tabs
   - -Wredundant-constraints
   - -Wincomplete-record-updates
-  - -Wincomplete-uni-patterns
   - -Wunused-type-patterns
+  - -O2
+
+default-extensions:
+  - StrictData

protocol/agent-protocol.md

@@ -1,3 +1,5 @@
+Version 5, 2024-06-22
+
 # SMP agent protocol - duplex communication over SMP protocol
 
 ## Table of contents
@@ -5,69 +7,61 @@
 - [Abstract](#abstract)
 - [SMP agent](#smp-agent)
 - [SMP servers management](#smp-servers-management)
-- [SMP agent protocol components](#smp-agent-protocol-components)
+- [SMP agent protocol scope](#smp-agent-protocol-scope)
 - [Duplex connection procedure](#duplex-connection-procedure)
+- [Contact addresses](#contact-addresses)
 - [Communication between SMP agents](#communication-between-smp-agents)
   - [Message syntax](#messages-between-smp-agents)
     - [HELLO message](#hello-message)
-    - [REPLY message](#reply-message)
-    - [MSG message](#msg-message)
-    - [INV message](#inv-message)
-    - [ACK message](#ack-message)
-    - [NEW message](#new-message)
-    - [DEL message](#del-message)
-- [SMP agent commands](#smp-agent-commands)
-  - [Client commands and server responses](#client-commands-and-server-responses)
-    - [NEW command and INV response](#new-command-and-inv-response)
-    - [JOIN command](#join-command)
-    - [CONF notification and LET command](#conf-notification-and-let-command)
-    - [REQ notification and ACPT command](#req-notification-and-acpt-command)
-    - [INFO and CON notifications](#info-and-con-notifications)
-    - [SUB command](#sub-command)
-    - [SEND command and MID, SENT and MERR responses](#send-command-and-mid-sent-and-merr-responses)
-    - [MSG notification](#msg-notification)
-    - [END notification](#end-notification)
-    - [OFF command](#off-command)
-    - [DEL command](#del-command)
-- [Connection request](#connection-request)
+    - [A_MSG message](#a_msg-message)
+    - [A_RCVD message](#a_rcvd-message)
+    - [EREADY message](#eready-message)
+    - [A_QCONT message](#a_qcont-message)
+    - [Rotating messaging queue](#rotating-messaging-queue)
+- [End-to-end encryption](#end-to-end-encryption)
+- [Connection link: 1-time invitation and contact address](#connection-link-1-time-invitation-and-contact-address)
+- [Appendix A: SMP agent API](#smp-agent-api)
+  - [API functions](#api-functions)
+  - [API events](#api-events)
 
 ## Abstract
 
 The purpose of SMP agent protocol is to define the syntax and the semantics of communications between the client and the agent that connects to [SMP](./simplex-messaging.md) servers.
 
 It provides:
-- protocol to create and manage bi-directional (duplex) connections between the users of SMP agents consisting of two (or more) separate unidirectional (simplex) SMP queues, abstracting away multiple steps required to establish bi-directional connections and any information about the servers location from the users of the agent protocol.
+- API to create and manage bi-directional (duplex) connections between the users of SMP agents consisting of two (or more) separate unidirectional (simplex) SMP queues, abstracting away multiple steps required to establish bi-directional connections and any information about the servers location from the users of the agent protocol.
 - management of E2E encryption between SMP agents, generating ephemeral asymmetric keys for each connection.
 - SMP command authentication on SMP servers, generating ephemeral keys for each SMP queue.
 - TCP/TLS transport handshake with SMP servers.
 - validation of message integrity.
 
-SMP agent protocol provides no encryption or security on the client side - it is assumed that the agent is executed in the trusted and secure environment, in one of three ways:
-- via TCP network using secure connection.
-- via local port (when the agent runs on the same device as a separate process).
-- via agent library, when the agent logic is included directly into the client application - [SimpleX Chat for terminal](https://github.com/simplex-chat/simplex-chat) uses this approach.
+SMP agent API provides no security between the agent and the client - it is assumed that the agent is executed in the trusted and secure environment, via the agent library, when the agent logic is included directly into the client application - [SimpleX Chat for terminal](https://github.com/simplex-chat/simplex-chat) uses this approach.
 
 ## SMP agent
 
-SMP agents communicate with each other via SMP servers using [simplex messaging protocol (SMP)](./simplex-messaging.md) according to the commands received from its users. This protocol is a middle layer in SimpleX protocols (above SMP protocol but below any application level protocol) - it is intended to be used by client-side applications that need secure asynchronous bi-directional communication channels ("connections").
+SMP agents communicate with each other via SMP servers using [simplex messaging protocol (SMP)](./simplex-messaging.md) according to the API calls used by the client applications. This protocol is a middle layer in SimpleX protocols (above SMP protocol but below any application level protocol) - it is intended to be used by client-side applications that need secure asynchronous bi-directional communication channels ("connections").
 
 The agent must have a persistent storage to manage the states of known connections and of the client-side information of SMP queues that each connection consists of, and also the buffer of the most recent sent and received messages. The number of the messages that should be stored is implementation specific, depending on the error management approach that the agent implements; at the very least the agent must store the hashes and IDs of the last received and sent messages.
 
 ## SMP servers management
 
-SMP agent protocol commands do not contain the addresses of the SMP servers that the agent will use to create and use the connections (excluding the server address in queue URIs used in JOIN command). The list of the servers is a part of the agent configuration and can be dynamically changed by the agent implementation:
+SMP agent API does not use the addresses of the SMP servers that the agent will use to create and use the connections (excluding the server address in queue URIs used in JOIN command). The list of the servers is a part of the agent configuration and can be dynamically changed by the agent implementation:
 - by the client applications via any API that is outside of scope of this protocol.
 - by the agents themselves based on availability and latency of the configured servers.
 
-## SMP agent protocol components
+## SMP agent protocol scope
 
-SMP agent protocol has 3 main parts:
+SMP agent protocol has 2 main parts:
 
-- the syntax and semantics of the messages that SMP agents exchange with each other in order to:
+- the messages that SMP agents exchange with each other in order to:
   - negotiate establishing unidirectional (simplex) encrypted queues on SMP servers.
   - exchange client messages and delivery notifications, providing sequential message IDs and message integrity (by including the hash of the previous message).
-- the syntax and semantics of the commands that are sent by the agent clients to the agents. This protocol allows to create and manage multiple connections, each consisting of two or more SMP queues.
-- the syntax and semantics of the message that the clients of SMP agents should send out-of-band (as pre-shared "invitation" including queue URIs) to protect [E2E encryption][1] from active attacks ([MITM attacks][2]).
+  - re-negotiate messaging queues to use and connection e2e encryption.
+- the messages that the clients of SMP agents should send out-of-band (as pre-shared "invitation" including queue URIs) to protect [E2E encryption][1] from active attacks ([MITM attacks][2]).
+
+[Appendix A](#appendix-a-smp-agent-api) of this document describes:
+- the functional API used by the client application with the agent. This API allows to create and manage multiple connections, each consisting of two or more SMP queues.
+- events that the agent passes to the clients.
 
 ## Duplex connection procedure
 
@@ -75,54 +69,126 @@ SMP agent protocol has 3 main parts:
 
 The procedure of establishing a duplex connection is explained on the example of Alice and Bob creating a bi-directional connection consisting of two unidirectional (simplex) queues, using SMP agents (A and B) to facilitate it, and two different SMP servers (which could be the same server). It is shown on the diagram above and has these steps:
 
-1. Alice requests the new connection from the SMP agent A using SMP NEW command.
-2. Agent A creates an SMP connection on the server (using [SMP protocol](./simplex-messaging.md)) and responds to Alice with the invitation that contains queue information and the encryption key Bob's agent B should use. The invitation format is described in [Connection request](#connection-request).
-3. Alice sends the [connection request](#connection-request) to Bob via any secure channel (out-of-band message).
-4. Bob sends `JOIN` command with the connection request as a parameter to agent B to accept the connection.
-5. Establishing Alice's SMP queue (with SMP protocol commands):
-  - Agent B sends an "SMP confirmation" with SMP SEND command to the SMP queue specified in the connection request - SMP confirmation is an unauthenticated message with an ephemeral key that will be used to authenticate Bob's commands to the queue, as described in SMP protocol, and Bob's info (profile, public key for E2E encryption, etc.). This message is encrypted using key passed in the connection request (or with the derived key, in which case public key for key derivation should be sent in clear text).
-  - Agent A receives the SMP confirmation containing Bob's key and info as SMP MSG.
-  - Agent A notifies Alice sending REQ notification with Bob's info.
-  - Alice accepts connection request with ACPT command.
-  - Agent A secures the queue with SMP KEY command.
-  - Agent B tries sending authenticated SMP SEND command with agent `HELLO` message until it succeeds. Once it succeeds, Bob's agent "knows" the queue is secured.
-6. Agent B creates a new SMP queue on the server.
-7. Establish Bob's SMP queue:
-  - Agent B sends `REPLY` message (SMP SEND command) with the connection request to this 2nd queue to Alice's agent (via the 1st queue) - this connection request SHOULD use "simplex" URI scheme.
-  - Agent A, having received `REPLY` message, sends unauthenticated message (SMP SEND) to SMP queue with Alice agent's ephemeral key that will be used to authenticate Alice's commands to the queue, as described in SMP protocol, and Alice's info.
-  - Bob's agent receives the key and Alice's information and secures the queue (SMP KEY).
-  - Bob's agent sends the notification `INFO` with Alice's information to Bob.
-  - Alice's agent keeps sending `HELLO` message until it succeeds.
-8. Agents A and B notify Alice and Bob that connection is established.
-  - Once sending `HELLO` succeeds, Alice's agent sends to Alice `CON` notification that confirms that now both parties can communicate.
-  - Once Bob's agent receives `HELLO` from Alice's agent, it sends to Bob `CON` notification as well.
+1. Alice requests the new connection from the SMP agent A using agent `createConnection` api function.
+2. Agent A creates an SMP queue on the server (using [SMP protocol](./simplex-messaging.md) `NEW` command) and responds to Alice with the invitation that contains queue information and the encryption keys Bob's agent B should use. The invitation format is described in [Connection link](connection-link-1-time-invitation-and-contact-address).
+3. Alice sends the [connection link](#connection-link-1-time-invitation-and-contact-address) to Bob via any secure channel (out-of-band message) - as a link or as a QR code.
+4. Bob uses agent `joinConnection` api function with the connection link as a parameter to agent B to accept the connection.
+5. Agent B creates Bob's SMP reply queue with SMP server `NEW` command.
+6. Agent B confirms the connection: sends an "SMP confirmation" with SMP server `SEND` command to the SMP queue specified in the connection link - SMP confirmation is an unauthenticated message with an ephemeral key that will be used to authenticate Bob's commands to the queue, as described in SMP protocol, and Bob's info (profile, public key for E2E encryption, and the connection link to this 2nd queue to Agent A - this connection link SHOULD use "simplex" URI scheme). This message is encrypted using key passed in the connection link (or with the derived shared secret, in which case public key for key derivation should be sent in clear text).
+6. Alice confirms and continues the connection:
+  - Agent A receives the SMP confirmation containing Bob's key, reply queue and info as SMP server `MSG`.
+  - Agent A notifies Alice sending `CONF` notification with Bob's info.
+  - Alice allows connection to continue with agent `allowConnection` api function.
+  - Agent A secures the queue with SMP server `KEY` command.
+  - Agent A sends SMP confirmation with ephemeral sender key, ephemeral public encryption key and profile (but without reply queue).
+7. Agent B confirms the connection:
+  - receives the confirmation.
+  - sends the notification `INFO` with Alice's information to Bob.
+  - secures SMP queue that it sent to Alice in the first confirmation with SMP `KEY` command .
+  - sends `HELLO` message via SMP `SEND` command. This confirms that the reply queue is secured and also validates that Agent A secured the first SMP queue
+8. Agent A notifies Alice.
+  - receives `HELLO` message from Agent B.
+  - sends `HELLO` message to Agent B via SMP `SEND` command.
+  - sends `CON` notification to Alice, confirming that the connection is established.
+9. Agent B notifies Bob.
+  - Once Agent B receives `HELLO` from Agent A, it sends to Bob `CON` notification as well.
 
 At this point the duplex connection between Alice and Bob is established, they can use `SEND` command to send messages. The diagram also shows how the connection status changes for both parties, where the first part is the status of the SMP queue to receive messages, and the second part - the status of the queue to send messages.
 
 The most communication happens between the agents and servers, from the point of view of Alice and Bob there are 4 steps (not including notifications):
 
-1. Alice requests a new connection with `NEW` command and receives the invitation.
-2. Alice passes connection request out-of-band to Bob.
-3. Bob accepts the connection with `JOIN` command with the connection request to his agent.
-4. Alice accepts the connection with `ACPT` command.
+1. Alice requests a new connection with `createConnection` agent API function and receives the connection link.
+2. Alice passes connection link out-of-band to Bob.
+3. Bob accepts the connection with `joinConnection` agent API function with the connection link to his agent.
+4. Alice accepts the connection with `ACPT` agent API function.
 5. Both parties receive `CON` notification once duplex connection is established.
 
 Clients SHOULD support establishing duplex connection asynchronously (when parties are intermittently offline) by persisting intermediate states and resuming SMP queue subscriptions.
 
+## Fast duplex connection procedure
+
+Previously described duplex connection procedure requires sending 4 messages creating a bad UX for the users - it requires waiting until each party in online before the messages can be sent.
+
+It allows users validating connecting party profile before proceeding with the connection, but it turned out to be unnecessary UX step and is not used in the client applications.
+
+It also protects against an attacker who compromised TLS and uses the sender queue ID sent to the recipient to secure the queue before the sender can. This attack is very hard, and this accepting its risk is better than worse UX. Future protocol versions could mitigate this attack by encrypting entity IDs.
+
+Faster duplex connection process is possible with the `SKEY` command added in v9 of SMP protocol.
+
+![Fast duplex connection procedure](./diagrams/duplex-messaging/duplex-creating-fast.svg)
+
+1. Alice requests the new connection from the SMP agent A using agent `createConnection` api function
+2. Agent A creates an SMP queue on the server (using [SMP protocol](./simplex-messaging.md) `NEW` command with the flag allowing the sender to secure the queue) and responds to Alice with the invitation that contains queue information and the encryption keys Bob's agent B should use. The invitation format is described in [Connection link](connection-link-1-time-invitation-and-contact-address).
+3. Alice sends the [connection link](connection-link-1-time-invitation-and-contact-address) to Bob via any secure channel (out-of-band message) - as a link or as a QR code. This link contains the flag that the queue can be secured by the sender.
+4. Bob uses agent `joinConnection` api function with the connection link as a parameter to agent B to accept the connection.
+5. Agent B secures Alice's queue with SMP command `SKEY` - this command can be proxied.
+6. Agent B creates Bob's SMP reply queue with SMP server `NEW` command (with the flag allowing the sender to secure the queue).
+7. Agent B confirms the connection: sends an "SMP confirmation" with SMP server `SEND` command to the SMP queue specified in the connection link - SMP confirmation is an unauthenticated message with an ephemeral key that will be used to authenticate Bob's commands to the queue, as described in SMP protocol, and Bob's info (profile, public key for E2E encryption, and the connection link to this 2nd queue to Agent A - this connection link SHOULD use "simplex" URI scheme). This message is encrypted using key passed in the connection link (or with the derived shared secret, in which case public key for key derivation should be sent in clear text).
+8. Alice confirms the connection:
+  - Agent A receives the SMP confirmation containing Bob's key, reply queue and info as SMP server `MSG`.
+  - Agent A notifies Alice sending `CONF` notification with Bob's info (that indicates that Agent B already secured the queue).
+  - Alice allows connection to continue with agent `allowConnection` api function.
+  - Agent A secures Bob's queue with SMP command `SKEY`.
+  - Agent A sends SMP confirmation with ephemeral public encryption key and profile (but without reply queue, and without sender key).
+9. Agent A notifies Alice with `CON` notification.
+10. Agent B notifies Bob about connection success:
+  - receives confirmation message from Alice.
+  - sends the notification `INFO` with Alice's information to Bob.
+  - sends `CON` notification to Bob.
+
+## Contact addresses
+
+SMP agents support creating a special type of connection - a contact address - that allows to connect to multiple network users who can send connection requests by sending 1-time connection links to the message queue. 
+
+This connection address uses a messaging queue on SMP server to receive invitations to connect - see `agentInvitation` message below. Once connection request is accepted, a new connection is created and the address itself is no longer used to send the messages - deleting this address does not disrupt the connections that were created via it.
+
 ## Communication between SMP agents
 
 To establish duplex connections and to send messages on behalf of their clients, SMP agents communicate via SMP servers.
 
 Agents use SMP message client body (the part of the SMP message after header - see [SMP protocol](./simplex-messaging.md)) to transmit agent client messages and exchange messages between each other.
 
-Each SMP message client body, once decrypted, contains 3 parts (one of them may include binary message body), as defined by `decryptedSmpMessageBody` syntax:
+These messages are encrypted with per-queue shared secret using NaCL crypto_box and can be of 4 types, as defined by `decryptedSMPClientMessage`:
+- `agentConfirmation` - used when confirming SMP queues, contains connection information encrypted with double ratchet. This envelope can only contain `agentConnInfo` or `agentConnInfoReply` encrypted with double ratchet.
+- `agentMsgEnvelope` - contains different agent messages encrypted with double ratchet, as defined in `agentMessage`.
+- `agentInvitation` - sent to SMP queue that is used as contact address, does not use double ratchet.
+- `agentRatchetKey` - used to re-negotiate double ratchet encryption - can contain additional information in `agentRatchetKey`.
 
+```abnf
+decryptedSMPClientMessage = agentConfirmation / agentMsgEnvelope / agentInvitation / agentRatchetKey
+agentConfirmation = agentVersion %s"C" ("0" / "1" sndE2EEncryptionParams) encConnInfo
+agentVersion = 2*2 OCTET
+sndE2EEncryptionParams = TODO
+encConnInfo = doubleRatchetEncryptedMessage
+
+agentMsgEnvelope = agentVersion %s"M" encAgentMessage
+encAgentMessage = doubleRatchetEncryptedMessage
+
+agentInvitation = agentVersion %s"I" connReqLength connReq connInfo
+connReqLength = 2*2 OCTET ; Word16
+
+agentRatchetKey = agentVersion %s"R" rcvE2EEncryptionParams agentRatchetInfo
+rcvE2EEncryptionParams = TODO
+
+doubleRatchetEncryptedMessage = TODO
+```
+
+This syntax of decrypted SMP client message body is defined by `decryptedAgentMessage` below.
+
+Decrypted SMP message client body can be one of 4 types:
+- `agentConnInfo` - used by the initiating party when confirming reply queue - sent in `agentConfirmation` envelope.
+- `agentConnInfoReply` - used by accepting party, includes reply queue(s) in the initial confirmation - sent in `agentConfirmation` envelope.
+- `agentRatchetInfo` - used to pass additional information when renegotiating double ratchet encryption - sent in `agentRatchetKey` envelope.
+- `agentMessage` - all other agent messages.
+
+`agentMessage` contains these parts:
 - `agentMsgHeader` - agent message header that contains sequential agent message ID for a particular SMP queue, agent timestamp (ISO8601) and the hash of the previous message.
-- `agentMessage` - a command/message to the other SMP agent:
-  - to establish the connection with two SMP queues (`helloMsg`, `replyQueueMsg`)
-  - to send and to acknowledge user messages (`clientMsg`, `acknowledgeMsg`)
-  - to manage SMP queue rotation (`newQueueMessage`, `deleteQueueMsg`)
-  - to manage encryption key rotation (TODO)
+- `aMessage` - a command/message to the other SMP agent:
+  - to confirm the connection (`HELLO`).
+  - to send and to confirm reception of user messages (`A_MSG`, `A_RCVD`).
+  - to confirm that the new double ratchet encryption is agreed (`EREADY`).
+  - to notify another party that it can continue sending messages after queue capacity was exceeded (`A_QCONT`).
+  - to manage SMP queue rotation (`QADD`, `QKEY`, `QUSE`, `QTEST`).
 - `msgPadding` - an optional message padding to make all SMP messages have constant size, to prevent servers from observing the actual message size. The only case the message padding can be absent is when the message has exactly the maximum size, in all other cases the message MUST be padded to a fixed size.
 
 ### Messages between SMP agents
@@ -130,269 +196,160 @@ Each SMP message client body, once decrypted, contains 3 parts (one of them may
 Message syntax below uses [ABNF][3] with [case-sensitive strings extension][4].
 
 ```abnf
-decryptedSmpMessageBody = agentMsgHeader CRLF agentMessage CRLF msgPadding
-agentMsgHeader = agentMsgId SP previousMsgHash ; here `agentMsgId` is sequential ID set by the sending agent
-agentMsgId = 1*DIGIT
-previousMsgHash = encoded
-encoded = <base64 encoded>
+decryptedAgentMessage = agentConnInfo / agentConnInfoReply / agentRatchetInfo / agentMessage
+agentConnInfo = %s"I" connInfo
+connInfo = *OCTET
+agentConnInfoReply = %s"D" smpQueues connInfo
+agentRatchetInfo = %s"R" ratchetInfo
 
-agentMessage = helloMsg / replyQueueMsg /
-               clientMsg / invitationMsg /
-               newQueueMessage / deleteQueueMsg 
+agentMessage = %s"M" agentMsgHeader aMessage msgPadding
+agentMsgHeader = agentMsgId prevMsgHash
+agentMsgId = 8*8 OCTET ; Int64
+prevMsgHash = shortString
 
-msgPadding = *OCTET ; optional random bytes to get messages to the same size (as defined in SMP message size)
+aMessage = HELLO / A_MSG / A_RCVD / EREADY / A_QCONT /
+           QADD / QKEY / QUSE / QTEST
 
-helloMsg = %s"H"
+HELLO = %s"H"
 
-replyQueueMsg = %s"R" connectionRequest ; `connectionRequest` is defined below
-; this message can only be sent by the second connection party
+A_MSG = %s"M" userMsgBody
+userMsgBody = *OCTET
 
-clientMsg = %s"M" clientMsgBody
-clientMsgBody = *OCTET
+A_RCVD = %s"V" msgReceipt
+msgReceipt = agentMsgId msgHash rcptLength rcptInfo
 
-; TODO remove and move to "public" header
-invitationMsg = %s"INV" SP connReqInvitation SP connInfo
-; `connReqInvitation` and `connInfo` are defined below
+EREADY = %s"E" agentMsgId
 
-newQueueMsg = %s"N" queueURI
-; this message can be sent by any party to add SMP queue to the connection.
-; NOT SUPPORTED in the current implementation
+A_QCONT = %s"QC" sndQueueAddr
 
-deleteQueueMsg = %s"D" queueURI
-; notification that the queue with passed URI will be deleted
-; no need to notify the other party about suspending queue separately, as suspended and deleted queues are indistinguishable to the sender
-; NOT SUPPORTED in the current implementation
+QADD = %s"QA" sndQueues
+sndQueues = length 1*(newQueueUri replacedSndQueue)
+newQueueUri = clientVRange smpServer senderId dhPublicKey [sndSecure]
+dhPublicKey = length x509encoded
+sndSecure = "T"
+replacedSndQueue = "0" / "1" sndQueueAddr
+
+QKEY = %s"QK" sndQueueKeys
+sndQueueKeys = length 1*(newQueueInfo senderKey)
+newQueueInfo = version smpServer senderId dhPublicKey [sndSecure]
+senderKey = length x509encoded
+
+QUSE = %s"QU" sndQueuesReady
+sndQueuesReady = length 1*(sndQueueAddr primary)
+primary = %s"T" / %s"F"
+
+QTEST = %s"QT" sndQueueAddrs
+sndQueueAddrs = length 1*sndQueueAddr
+
+sndQueueAddr = smpServer senderId
+smpServer = hosts port keyHash
+hosts = length 1*host
+host = shortString
+port = shortString
+keyHash = shortString
+senderId = shortString
+
+clientVRange = version version
+version = 2*2 OCTET
+
+msgPadding = *OCTET
+rcptLength = 2*2 OCTET
+shortString = length *OCTET
+length = 1*1 OCTET
 ```
 
 #### HELLO message
 
-This is the first message that both agents send after the respective SMP queue is secured by the receiving agent (see diagram). It MAY contain the public key that the recipient would use to verify messages signed by the sender.
+This is the first message that both agents send after the respective SMP queue is secured by the receiving agent (see diagram).
 
-Sending agent might need to retry sending HELLO message, as it would not have any other confirmation that the queue is secured other than the success of sending this message with the signed SMP SEND command.
+This message is not used with [fast duplex connection](#fast-duplex-connection-procedure).
 
-#### REPLY message
+#### A_MSG message
 
-This is the message that is sent by the agent that received an out-of-band connection request to pass the connection request for the reply SMP queues to the agent that originated the connection (see diagram).
+This is the agent envelope used to send client messages once the connection is established. This is different from the MSG sent by SMP server to the agent and MSG event from SMP agent to the client that are sent in different contexts.
 
-#### MSG message
+#### A_RCVD message
 
-This is the agent envelope used to send client messages once the connection is established. Do not confuse it with the MSG response from SMP server to the agent and MSG response from SMP agent to the client that are sent in different contexts.
+This message is sent to confirm the client message reception. It includes received message number and message hash.
 
-#### INV message
+#### EREADY message
 
-This message is sent to the SMP queue(s) in `connReqContact`, to establish a new connection via existing unsecured queue, that acts as a permanent connection link of a user.
+This message is sent after re-negotiating a new double ratchet encryption with `agentRatchetKey`.
 
-#### ACK message
+#### A_QCONT message
 
-This message is sent to confirm the client message reception. It includes received message number, message hash and the reception status.
+This message is sent to notify the sender client that it can continue sending the messages after queue capacity was exhausted.
 
-#### NEW message
+### Rotating messaging queue
 
-This message is sent to add an additional SMP queue to the connection. Unlike REPLY message it can be sent at any time.
+SMP agents SHOULD support 4 messages to rotate message reception to another messaging server:
+`QADD`: add the new queue address(es) to the connection - sent by the client that initiates rotation.
+`QKEY`: pass sender's key via existing connection (SMP confirmation message will not be used, to avoid the same "race" of the initial key exchange that would create the risk of intercepting the queue for the attacker) - sent by the client accepting the rotation
+`QUSE`: instruct the sender to use the new queue with sender's queue ID as parameter. From this point some messages can be sent to both the new queue and the old queue.
+`QTEST`: send test message to the new connection. Any other message can be sent if available to continue rotation, the absence of this message is not an error. Once this message is successfully sent the sender will stop using the old queue. Once this message (or any other message in the new queue) is received, the recipient will stop using the old queue and delete it.
 
-#### DEL message 
+**Queue rotation procedure**
 
-This message is sent to notify that the queue with passed URI will be deleted - having received this message, the receiving agent should no longer send messages to this queue. In case it was the last remaining send queue in the duplex connection, the agent MAY also delete the reply queue(s) in the connection.
+![Queue rotation procedure](./diagrams/duplex-messaging/queue-rotation.svg)
 
-## SMP agent commands
+`SKEY` command added in v9 of SMP protocol allows for faster queue rotation procedure.
 
-This part describes the transmissions between users and client-side SMP agents: commands that the users send to create and operate duplex connections and SMP agent responses and messages they deliver.
+**Fast queue rotation procedure**
 
-Commands syntax below is provided using [ABNF][3] with [case-sensitive strings extension][4].
+![Fast queue rotation procedure](./diagrams/duplex-messaging/queue-rotation-fast.svg)
 
-Each transmission between the user and SMP agent must have this format/syntax:
+## End-to-end encryption
 
-```abnf
-agentTransmission = [corrId] CRLF [connId] CRLF agentCommand
+Messages between SMP agents have two layers of e2e encryption:
+- simple encryption agreed in SMP protocol with a fixed key agreed when the messaging queue is agreed by parties.
+- post-quantum resistant augmented double ratchet algorithm (PQDR) specified in [this document](./pqdr.md).
 
-corrId = 1*(%x21-7F) ; any characters other than control/whitespace
+The protocol supports adding and removing post-quantum KEM primitive to the key agreement in double ratchet:
+- to support migration of pre-existing connections to PQDR.
+- to be able to disable PQ key agreement.
+- to be able to use invitation links and contact addresses without large PQ keys.
 
-connId = encoded
+Possible scenarios below show the possible states of PQ key agreement, assuming that both clients support it.
 
-agentCommand = (userCmd / agentMsg) CRLF
-userCmd = newCmd / joinCmd / letCmd / acceptCmd / subscribeCmd / sendCmd / acknowledgeCmd / suspendCmd / deleteCmd
-agentMsg = invitation / confMsg / connReqMsg / connInfo / connected / unsubscribed / connDown / connUp / messageId / sent / messageError / message / received / ok / error
+Possible options for each stage are:
+- no KEM encapsulation key was sent (No PQ key),
+- only KEM encapsulation key was sent, but not ciphertext yet (PQ key sent),
+- both KEM encapsulation key from one KEM agreement and ciphertext from the previous agreement were sent (PQ key + PQ ct sent).
 
-newCmd = %s"NEW" SP connectionMode [SP %s"NO_ACK"] ; response is `invitation` or `error`
-; NO_ACK parameter currently not supported
+`+` in the table means that this scenario is possible, and `-` - that it is not possible.
 
-connectionMode = %s"INV" / %s"CON"
+| Connection stage                                       | No PQ key        | PQ key sent      | PQ key + PQ ct sent |
+|:------------------------------------------------------:|:----------------:|:----------------:|:-------------------:|
+| invitation                                             |         +        |         +        |          -          |
+| confirmation, in reply to: <br>no-pq inv <br>pq inv    | &nbsp;<br>+<br>+ | &nbsp;<br>+<br>- | &nbsp;<br>-<br>+    |
+| 1st msg, in reply to: <br>no-pq conf <br>pq/pq+ct conf | &nbsp;<br>+<br>+ | &nbsp;<br>+<br>- | &nbsp;<br>-<br>+    |
+| Nth msg, in reply to: <br>no-pq msg <br>pq/pq+ct msg   | &nbsp;<br>+<br>+ | &nbsp;<br>+<br>- | &nbsp;<br>-<br>+    |
 
-invitation = %s"INV" SP connectionRequest ; `connectionRequest` is defined below
+These scenarios can be reduced to:
+1. initial invitation optionally has PQ key, but must not have ciphertext.
+2. all subsequent messages should be allowed without PQ key/ciphertext, but:
+  - if the previous message had PQ key or PQ key with ciphertext, they must either have no PQ key, or have PQ key with ciphertext (PQ key without ciphertext is an error).
+  - if the previous message had no PQ key, they must either have no PQ key, or have PQ key without ciphertext (PQ key with ciphertext is an error).
 
-confMsg = %s"CONF" SP confirmationId SP msgBody
-; msgBody here is any binary information identifying connection request
+The rules for calculating the shared secret for received/sent messages are (assuming received message is valid according to the above rules):
 
-letCmd = %s"LET" SP confirmationId SP msgBody
-; msgBody here is any binary information identifying connecting party
+|  sent msg > <br>V received msg | no-pq       | pq      | pq+ct           |
+|:------------------------------:|:-----------:|:-------:|:---------------:|
+| no-pq                          | DH / DH     | DH / DH | err             |
+| pq (sent msg was NOT pq)       | DH / DH     | err     | DH / DH+KEM     |
+| pq+ct (sent msg was NOT no-pq) | DH+KEM / DH | err     | DH+KEM / DH+KEM |
 
-confirmationId = 1*DIGIT
+To summarize, the upgrade to DH+KEM secret happens in a sent message that has PQ key with ciphertext sent in reply to message with PQ key only (without ciphertext), and the downgrade to DH secret happens in the message that has no PQ key.
 
-connReqMsg = %s"REQ" SP invitationId SP msgBody
-; msgBody here is any binary information identifying connection request
+## Connection link: 1-time invitation and contact address
 
-acceptCmd = %s"ACPT" SP invitationId SP msgBody
-; msgBody here is any binary information identifying connecting party
+Connection links are generated by SMP agent in response to `createConnection` api call, used by another party user with `joinConnection` api, and then another connection link is sent by the agent in `agentConnInfoReply` and used by the first party agent to connect to the reply queue (the second part of the process is invisible to the users).
 
-invitationId = 1*DIGIT
-
-connInfo = %s"INFO" SP msgBody
-; msgBody here is any binary information identifying connecting party
-
-connected = %s"CON"
-
-subscribeCmd = %s"SUB" ; response is `ok` or `error`
-
-unsubscribed = %s"END"
-; when another agent (or another client of the same agent)
-; subscribes to the same SMP queue on the server
-
-connDown = %s"DOWN"
-; lost connection (e.g. because of Internet connectivity or server is down)
-
-connUp = %s"UP"
-; restored connection
-
-joinCmd = %s"JOIN" SP connectionRequest SP connInfo [SP %s"NO_REPLY"] [SP %s"NO_ACK"]
-; `connectionRequest` and `connInfo` are defined below
-; response is `connected` or `error`
-; parameters NO_REPLY and NO_ACK are currently not supported
-
-suspendCmd = %s"OFF" ; can be sent by either party, response `ok` or `error`
-
-deleteCmd = %s"DEL" ; can be sent by either party, response `ok` or `error`
-
-sendCmd = %s"SEND" SP msgBody
-; send syntax is similar to that of SMP protocol, but it is wrapped in SMP message
-msgBody = stringMsg | binaryMsg
-stringMsg = ":" string ; until CRLF in the transmission
-string = *(%x01-09 / %x0B-0C / %x0E-FF %) ; any characters other than NUL, CR and LF
-binaryMsg = size CRLF msgBody CRLF ; the last CRLF is in addition to CRLF in the transmission
-size = 1*DIGIT ; size in bytes
-msgBody = *OCTET ; any content of specified size - safe for binary
-
-messageId = %s"MID" SP agentMsgId
-
-sent = %s"SENT" SP agentMsgId
-
-messageError = %s"MERR" SP agentMsgId SP <errorType>
-
-message = %s"MSG" SP msgIntegrity SP recipientMeta SP brokerMeta SP senderMeta SP binaryMsg
-recipientMeta = %s"R=" agentMsgId "," agentTimestamp ; receiving agent message metadata 
-brokerMeta = %s"B=" brokerMsgId "," brokerTimestamp ; broker (server) message metadata
-senderMeta = %s"S=" agentMsgId ; sending agent message ID 
-brokerMsgId = encoded
-brokerTimestamp = <date-time>
-msgIntegrity = ok / msgIntegrityError
-
-msgIntegrityError = %s"ERR" SP msgIntegrityErrorType
-msgIntegrityErrorType = skippedMsgErr / badMsgIdErr / badHashErr
-
-skippedMsgErr = %s"NO_ID" SP missingFromMsgId SP missingToMsgId
-badMsgIdErr = %s"ID" SP previousMsgId ; ID is lower than the previous
-badHashErr = %s"HASH"
-
-missingFromMsgId = agentMsgId
-missingToMsgId = agentMsgId
-previousMsgId = agentMsgId
-
-acknowledgeCmd = %s"ACK" SP agentMsgId ; ID assigned by receiving agent (in MSG "R")
-
-received = %s"RCVD" SP agentMsgId SP msgIntegrity
-; ID assigned by sending agent (in SENT response)
-; currently not implemented
-
-msgStatus = ok | error
-
-ok = %s"OK"
-
-error = %s"ERR" SP <errorType>
-```
-
-### Client commands and server responses
-
-#### NEW command and INV response
-
-`NEW` command is used to create a connection and a connection request to be sent out-of-band to another protocol user (the joining party). It should be used by the client of the agent that initiates creating a duplex connection (the initiating party).
-
-`INV` response is sent by the agent to the client of the initiating party.
-
-`NEW` command has `connectionMode` parameter to define the connection mode - to be used to communicate with a single contact (invitation mode, `connectionMode` is `INV`) or to accept connection requests from anybody (contact mode, `connectionMode` is `CON`). The type of connection request is determined by `connectionMode` parameter.
-
-#### JOIN command
-
-It is used to create a connection and accept the connection request received out-of-band. It should be used by the client of the agent that accepts the connection (the joining party).
-
-#### CONF notification and LET command
-
-When the joining party uses `JOIN` command to accept connection invitation created with `NEW INV` command, the initiating party will receive `CONF` notification with some numeric identifier and an additional binary information, that can be used to identify the joining party or for any other purpose.
-
-To continue with the connection the initiating party should use `LET` command.
-
-#### REQ notification and ACPT command
-
-When the joining party uses `JOIN` command to connect to the contact created with `NEW CON` command, the initiating party will receive `REQ` notification with some numeric identifier and an additional binary information, that can be used to identify the joining party or for any other purpose.
-
-To continue with the connection the party that created the contact should use `ACPT` command.
-
-#### INFO and CON notifications
-
-After the initiating party proceeds with the connection using `ACPT` command, the joining party will receive `INFO` notification that can be used to identify the initiating party or for any other purpose.
-
-Once the connection is established and ready to accept client messages, both agents will send `CON` notification to their clients.
-
-#### SUB command
-
-This command can be used by the client to resume receiving messages from the connection that was created in another TCP/client session. Agent response to this command can be `OK` or `ERR` in case connection does not exist (or can only be used to send connections - e.g. when the reply queue was not created).
-
-#### SEND command and MID, SENT, RCVD and MERR responses
-
-`SEND` command is used by the client to send messages.
-
-`MID` response with the message ID (the sequential message number that includes both sent and received messages in the connection) is sent to the client to confirm that the message is accepted by the agent, before it is sent to the SMP server.
-
-`SENT` notification is sent by the agent to confirm that the message was delivered to at least one of SMP servers. This notification contains the same message ID as `MID` notification. `SENT` notification, depending on network availability, can be sent at any time later, potentially in the next client session.
-
-`RCVD` notification is sent by the agent when it receives `ACK` message from the receiving agent. This notification contains reception status, only one successful notification will be sent, and multiple error notifications will be sent in case `ACK` had error status.
-
-In case of the failure to send the message for any other reason than network connection or message queue quota - e.g. authentication error (`ERR AUTH`) or syntax error (`ERR CMD error`), the agent will send to the client `MERR` notification with the message ID, and this message delivery will no longer be attempted to this SMP queue.
-
-#### MSG notification
-
-It is sent by the agent to the client when agent receives the message from the SMP server. It has message ID and timestamp from both the receiving and sending agents and from SMP server:
-- recipient agent ID is intended to be used to refer to the message in the future.
-- sender agent ID is intended to be used to identify any missed / skipped message(s)
-- broker ID should be used to detect duplicate deliveries (it would happen if TCP connection is lost before the message is acknowledged by the agent - see [SMP protocol](./simplex-messaging.md))
-
-#### END notification
-
-It is sent by the agent to the client when agent receives SMP protocol `END` notification from SMP server. It indicates that another agent has subscribed to the same SMP queue on the server and the server terminated the subscription of the current agent.
-
-#### DOWN and UP notifications
-
-These notifications are sent when server or network connection is, respectively, `DOWN` or back `UP`.
-
-All the subscriptions made in the current client session will be automatically resumed when `UP` notification is received.
-
-#### OFF command
-
-It is used to suspend the receiving SMP queue - sender will no longer be able to send the messages to the connection, but the recipient can retrieve the remaining messages. Agent response to this command can be `OK` or `ERR`. This command is irreversible.
-
-#### DEL command
-
-It is used to delete the connection and all messages in it, as well as the receiving SMP queue and all messages in it that were remaining on the server. Agent response to this command can be `OK` or `ERR`. This command is irreversible.
-
-## Connection request
-
-Connection request `connectionRequest` is generated by SMP agent in response to `newCmd` command (`"NEW"`), used by another party user with `joinCmd` command (`"JOIN"`), and then another connection request is sent by the agent in `replyQueueMsg` and used by the first party agent to connect to the reply queue (the second part of the process is invisible to the users).
-
-Connection request syntax:
+Connection link syntax:
 
 ```
-connectionRequest = connectionScheme "/" connReqType "#/?smp=" smpQueues "&e2e=" e2eEncryption
-connReqType = %s"invitation" / %s"contact"
-; this parameter has the same meaning as connectionMode in agent commands
-; `NEW INV` creates `invitation` connection request, `NEW CON` - `contact`
+connectionLink = connectionScheme "/" connLinkType "#/?smp=" smpQueues "&e2e=" e2eEncryption
+connLinkType = %s"invitation" / %s"contact"
 connectionScheme = (%s"https://" clientAppServer) | %s"simplex:"
 clientAppServer = hostname [ ":" port ]
 ; client app server, e.g. simplex.chat
@@ -407,12 +364,112 @@ smpQueue = <URL-encoded queueURI defined in SMP protocol>
 
 All parameters are passed via URI hash to avoid sending them to the server (in case "https" scheme is used) - they can be used by the client-side code and processed by the client application. Parameters `smp` and `e2e` can be present in any order, any unknown additional parameters SHOULD be ignored.
 
-`clientAppServer` is not an SMP server - it is a server that shows the instruction on how to download the client app that will connect using this connection request. This server can also host a mobile or desktop app manifest so that this link is opened directly in the app if it is installed on the device.
+`clientAppServer` is not an SMP server - it is a server that shows the instruction on how to download the client app that will connect using this connection link. This server can also host a mobile or desktop app manifest so that this link is opened directly in the app if it is installed on the device.
 
 "simplex" URI scheme in `connectionProtocol` can be used instead of client app server, to connect without creating any web traffic. Client apps MUST support this URI scheme.
 
 See SMP protocol [out-of-band messages](./simplex-messaging.md#out-of-band-messages) for syntax of `queueURI`.
 
+## Appendix A: SMP agent API
+
+The exact specification of agent library API and of the events that the agent sends to the client application is out of scope of the protocol specification.
+
+The list of some of the API functions and events below is supported by the reference implementation, and they are likely to be required by the client applications.
+
+### API functions
+
+The list of APIs below is not exhaustive and provided for information only. Please consult the source code for more information.
+
+#### Create conection
+
+`createConnection` api is used to create a connection - it returns the connection link that should be sent out-of-band to another protocol user (the joining party). It should be used by the client of the agent that initiates creating a duplex connection (the initiating party).
+
+This api is also used to create a contact address - a special connection that can be used by multiple people to connect to the user.
+
+Some communication scenarios may require fault-tolerant mechanism of creating connections that retries on network failures and continue retrying after the client is restarted. Such asynchronous API would return its result via `INV` event once it succeeds.
+
+#### Join connection
+
+`joinConnection` is used to create a connection record and accept the connection invitation received out-of-band. It should be used by the client of the agent that accepts the connection (the joining party).
+
+This api can also be required as asynchronous, in which case `OK` event will be dispatched to the client to indicate the success or `ERR` in case it permanently failed (e.g., in case connection was deleted by another party).
+
+#### Allow connection
+
+Once the client receives `CONF` event, it should use synchronous `allowConnection` api to proceed with the connection (both for the [standard](#duplex-connection-procedure) and for the [fast duplex procedure](#fast-duplex-connection-procedure)).
+
+In case this API is used as asynchronous it will return its result via `OK` or `ERR` event.
+
+#### Accept and reject connection requests
+
+Connection requests are delivered to the client application via `REQ` event.
+
+Client can `acceptContact` and `rejectContact`, with `OK` and `ERR` events in case of asynchronous calls.
+
+#### Send message
+
+`sendMessage` api is always asynchronous. The api call returns message ID, `SENT` event once the message is sent to the server, `MWARN` event in case of temporary delivery failure that can be resolved by the user (e.g., by connecting via Tor or by upgrading the client) and `MERR` in case of permanent delivery failure.
+
+#### Acknowledge received message
+
+Messages are delivered to the client application via `MSG` event.
+
+Client application must always `ackMessage` to receive the next one - failure to call it in reference implementation will prevent the delivery of subsequent messages until the client reconnects to the server.
+
+This api is also used to acknowledge message delivery to the sending party - that party client application will receive `RCVD` event.
+
+#### Subscribe connection
+
+`subscribeConnection` api is used by the client to resume receiving messages from the connection that was created in another TCP/client session.
+
+#### Get notification message
+
+`getNotificationMessage` is used by push notification subsystem of the client application to receive the message from a specific messaging queue mentioned in the notification. The client application would receive `MSG` and any other events from the agent, and then `MSGNTF` event once the message related to this notification is received.
+
+#### Rotate message queue to another server
+
+`switchConnection` api is used to rotate connection queues to another messaging server.
+
+#### Renegotiate e2e encryption
+
+`synchronizeRatchet` api is used to re-negotiate double ratchet encryption for the connection.
+
+#### Delete connection
+
+`deleteConnection` api is used to delete connection. In case of asynchronous call, the connection deletion will be confirmed with `DEL_RCVQ` and `DEL_CONN` events.
+
+#### Suspend connection
+
+`suspendConnection` api is used to prevent any further messages delivered to the connection without deleting it.
+
+### API events
+
+Agent API uses these events dispatch to notify client application about events related to the connections:
+- `INV` - connection invitation or connection address URI after connection is created.
+- `CONF` - confirmation that connection is accepted by another party. When the accepting party uses `joinConnection` api to accept connection invitation, the initiating party will receive `CONF` notification with some identifier and additional information from the accepting party (e.g., profile). To continue the connection the initiating party client should use `allowConnection` api.
+- `REQ` - connection request is sent when another party uses `joinConnection` api with contact address. The client application can use `acceptContact` or `rejectContact` api.
+- `INFO` - information from the party that initiated the connection with `createConnection` sent to the party accepting the connection with `joinConnection`.
+- `CON` - notification that connection is established sent to both parties of the connection.
+- `END` - notification that connection subscription is terminated when another client subscribed to the same messaging queue.  
+- `DOWN` - notification that connection server is temporarily unavailable.
+- `UP` - notification that the subscriptions made in the current client session are resumed after the server became available.
+- `SWITCH` - notification about queue rotation process.
+- `RSYNC` - notification about e2e encryption re-negotiation process.
+- `SENT` - notification to confirm that the message was delivered to at least one of SMP servers. This notification contains the same message ID as returned to `sendMessage` api. `SENT` notification, depending on network availability, can be sent at any time later, potentially in the next client session.
+- `MWARN` - temporary delivery failure that can be resolved by the user (e.g., by connecting via Tor or by upgrading the client).
+- `MERR` - notification about permanent message delivery failure.
+- `MERRS` - notification about permanent message delivery failure for multiple messages (e.g., when multiple messages expire).
+- `MSG` - sent when agent receives the message from the SMP server.
+- `MSGNTF` - sent after agent received and processed the message referenced in the push notification.
+- `RCVD` - notification confirming message receipt by another party.
+- `QCONT` - notification that the agent continued sending messages after queue capacity was exceeded and recipient received all messages.
+- `DEL_RCVQ` - confirmation that message queue was deleted.
+- `DEL_CONN` - confirmation that connection was deleted.
+- `OK` - confirmation that asynchronous api call was successful.
+- `ERR` - error of asynchronous api call or some other error event.
+
+This list of events is not exhaustive and provided for information only. Please consult the source code for more information.
+
 [1]: https://en.wikipedia.org/wiki/End-to-end_encryption
 [2]: https://en.wikipedia.org/wiki/Man-in-the-middle_attack
 [3]: https://tools.ietf.org/html/rfc5234

protocol/diagrams/duplex-messaging/duplex-creating-fast.mmd

@@ -0,0 +1,65 @@
+sequenceDiagram
+  participant A as Alice
+  participant AA as Alice's<br>agent
+  participant AS as Alice's<br>server
+  participant BS as Bob's<br>server
+  participant BA as Bob's<br>agent
+  participant B as Bob
+
+  note over AA, BA: status (receive/send): NONE/NONE
+
+  note over A, AA: 1. request connection<br>from agent
+  A ->> AA: createConnection
+ 
+  note over AA, AS: 2. create Alice's SMP queue
+  AA ->> AS: NEW: create SMP queue<br>allow sender to secure
+  AS ->> AA: IDS: SMP queue IDs
+  note over AA: status: NEW/NONE
+
+  AA ->> A: INV: invitation<br>to connect
+
+  note over A, B: 3. out-of-band invitation
+  A ->> B: OOB: invitation to connect
+
+  note over BA, B: 4. accept connection
+  B ->> BA: joinConnection:<br>via invitation info
+  note over BA: status: NONE/NEW
+
+  note over BA, AS: 5. secure Alice's SMP queue
+  BA ->> AS: SKEY: secure queue (this command needs to be proxied)
+  note over BA: status: NONE/SECURED
+
+  note over BA, BS: 6. create Bob's SMP queue
+  BA ->> BS: NEW: create SMP queue<br>allow sender to secure
+  BS ->> BA: IDS: SMP queue IDs
+  note over BA: status: NEW/SECURED
+
+  note over BA, AA: 7. confirm Alice's SMP queue
+  BA ->> AS: SEND: Bob's info without sender's key (SMP confirmation with reply queues)
+  note over BA: status: NEW/CONFIRMED
+
+  AS ->> AA: MSG: Bob's info without<br>sender server key
+  note over AA: status: CONFIRMED/NEW
+  AA ->> AS: ACK: confirm message
+  AA ->> A: CONF: connection request ID<br>and Bob's info
+  A -> AA: allowConnection: accept connection request,<br>send Alice's info
+  
+  note over AA, BS: 8. secure Bob's SMP queue
+  AA ->> BS: SKEY: secure queue (this command needs to be proxied)
+  note over BA: status: CONFIRMED/SECURED
+
+  AA ->> BS: SEND: Alice's info without sender's server key (SMP confirmation without reply queues)
+  note over AA: status: CONFIRMED/CONFIRMED
+
+  note over AA, A: 9. notify Alice<br>about connection success<br>(no HELLO needed in v6)
+  AA ->> A: CON: connected
+  note over AA: status: ACTIVE/ACTIVE
+
+  note over BA, B: 10. notify Bob<br>about connection success
+  BS ->> BA: MSG: Alice's info without<br>sender's server key
+  note over BA: status: CONFIRMED/CONFIRMED
+  BA ->> B: INFO: Alice's info
+  BA ->> BS: ACK: confirm message
+
+  BA ->> B: CON: connected
+  note over BA: status: ACTIVE/ACTIVE

protocol/diagrams/duplex-messaging/duplex-creating-v2.mmd

@@ -1,71 +0,0 @@
-sequenceDiagram
-  participant A as Alice
-  participant AA as Alice's<br>agent
-  participant AS as Alice's<br>server
-  participant BS as Bob's<br>server
-  participant BA as Bob's<br>agent
-  participant B as Bob
-
-  note over AA, BA: status (receive/send): NONE/NONE
-
-  note over A, AA: 1. request connection<br>from agent
-  A ->> AA: NEW: create<br>duplex connection
- 
-  note over AA, AS: 2. create Alice's SMP queue
-  AA ->> AS: NEW: create SMP queue
-  AS ->> AA: IDS: SMP queue IDs
-  note over AA: status: NEW/NONE
-
-  AA ->> A: INV: invitation<br>to connect
-
-  note over A, B: 3. out-of-band invitation
-  A ->> B: OOB: invitation to connect
-
-  note over BA, B: 4. accept connection
-  B ->> BA: JOIN:<br>via invitation info
-  note over BA: status: NONE/NEW
-
-  note over BA, BS: 5. create Bob's SMP queue
-  BA ->> BS: NEW: create SMP queue
-  BS ->> BA: IDS: SMP queue IDs
-  note over BA: status: NEW/NEW
-
-  note over BA, AA: 6. establish Alice's SMP queue
-  BA ->> AS: SEND: Bob's info and sender server key (SMP confirmation with reply queues)
-  note over BA: status: NEW/CONFIRMED
-
-  AS ->> AA: MSG: Bob's info and<br>sender server key
-  note over AA: status: CONFIRMED/NONE
-  AA ->> AS: ACK: confirm message
-  AA ->> A: CONF: connection request ID<br>and Bob's info
-  A ->> AA: LET: accept connection request,<br>send Alice's info
-  AA ->> AS: KEY: secure queue
-  note over AA: status: SECURED/NONE
-
-  AA ->> BS: SEND: Alice's info and sender's server key (SMP confirmation without reply queues)
-  note over AA: status: SECURED/CONFIRMED
-
-  BS ->> BA: MSG: Alice's info and<br>sender's server key
-  note over BA: status: CONFIRMED/CONFIRMED
-  BA ->> B: INFO: Alice's info
-  BA ->> BS: ACK: confirm message
-  BA ->> BS: KEY: secure queue
-  note over BA: status: SECURED/CONFIRMED
-
-  BA ->> AS: SEND: HELLO: only needs to be sent once in v2
-
-  note over BA: status: SECURED/ACTIVE
-  note over BA, B: 7a. notify Bob<br>about connection success
-  BA ->> B: CON: connected
-
-  AS ->> AA: MSG: HELLO: Alice's agent<br>knows Bob can send
-  note over AA: status: SECURED/ACTIVE
-  AA ->> AS: ACK: confirm message
-  note over A, AA: 7a. notify Alice<br>about connection success
-  AA ->> A: CON: connected
-
-  AA ->> BS: SEND: HELLO: only needs to be sent once in v2
-  note over AA: status: ACTIVE/ACTIVE
-  BS ->> BA: MSG: HELLO: Bob's agent<br>knows Alice can send
-  note over BA: status: ACTIVE/ACTIVE
-  BA ->> BS: ACK: confirm message

protocol/diagrams/duplex-messaging/duplex-creating.mmd

@@ -8,8 +8,8 @@ sequenceDiagram
 
   note over AA, BA: status (receive/send): NONE/NONE
 
-  note over A, AA: 1. request connection from agent
-  A ->> AA: NEW: create<br>duplex connection
+  note over A, AA: 1. request connection<br>from agent
+  A ->> AA: createConnection
  
   note over AA, AS: 2. create Alice's SMP queue
   AA ->> AS: NEW: create SMP queue
@@ -17,63 +17,58 @@ sequenceDiagram
   note over AA: status: NEW/NONE
 
   AA ->> A: INV: invitation<br>to connect
-  note over AA: status: PENDING/NONE
 
   note over A, B: 3. out-of-band invitation
   A ->> B: OOB: invitation to connect
 
   note over BA, B: 4. accept connection
-  B ->> BA: JOIN:<br>via invitation info
+  B ->> BA: joinConnection:<br>via invitation info
   note over BA: status: NONE/NEW
 
-  note over BA, AA: 5. establish Alice's SMP queue
-  BA ->> AS: SEND: Bob's info and sender server key (SMP confirmation)
-  note over BA: status: NONE/CONFIRMED
-  activate BA
+  note over BA, BS: 5. create Bob's SMP queue
+  BA ->> BS: NEW: create SMP queue
+  BS ->> BA: IDS: SMP queue IDs
+  note over BA: status: NEW/NEW
+
+  note over BA, AA: 6. confirm Alice's SMP queue
+  BA ->> AS: SEND: Bob's info and sender server key (SMP confirmation with reply queues)
+  note over BA: status: NEW/CONFIRMED
+
   AS ->> AA: MSG: Bob's info and<br>sender server key
   note over AA: status: CONFIRMED/NONE
   AA ->> AS: ACK: confirm message
   AA ->> A: CONF: connection request ID<br>and Bob's info
-  A ->> AA: LET: accept connection request,<br>send Alice's info
+  A ->> AA: allowConnection: accept connection request,<br>send Alice's info
   AA ->> AS: KEY: secure queue
   note over AA: status: SECURED/NONE
 
-  BA ->> AS: SEND: HELLO: try sending until successful
-  deactivate BA
-  note over BA: status: NONE/ACTIVE
-  AS ->> AA: MSG: HELLO: Alice's agent<br>knows Bob can send
-  note over AA: status: ACTIVE/NONE
-  AA ->> AS: ACK: confirm message
+  AA ->> BS: SEND: Alice's info and sender's server key (SMP confirmation without reply queues)
+  note over AA: status: SECURED/CONFIRMED
 
-  note over BA, BS: 6. create Bob's SMP queue
-  BA ->> BS: NEW: create SMP queue
-  BS ->> BA: IDS: SMP queue IDs
-  note over BA: status: NEW/ACTIVE
-
-  note over AA, BA: 7. establish Bob's SMP queue
-  BA ->> AS: SEND: REPLY: invitation to the connect
-  note over BA: status: PENDING/ACTIVE
-  AS ->> AA: MSG: REPLY: invitation<br>to connect
-  note over AA: status: ACTIVE/NEW
-  AA ->> AS: ACK: confirm message
-
-  AA ->> BS: SEND: Alice's info and sender's server key
-  note over AA: status: ACTIVE/CONFIRMED
-  activate AA
+  note over BA, AA: 7. confirm Bob's SMP queue
   BS ->> BA: MSG: Alice's info and<br>sender's server key
-  note over BA: status: CONFIRMED/ACTIVE
+  note over BA: status: CONFIRMED/CONFIRMED
   BA ->> B: INFO: Alice's info
   BA ->> BS: ACK: confirm message
   BA ->> BS: KEY: secure queue
+  note over BA: status: SECURED/CONFIRMED
+
+  BA ->> AS: SEND: HELLO message
+
   note over BA: status: SECURED/ACTIVE
 
-  AA ->> BS: SEND: HELLO: try sending until successful
-  deactivate AA
+  AS ->> AA: MSG: HELLO: Alice's agent<br>knows Bob can send
+  note over AA: status: SECURED/ACTIVE
+  AA ->> AS: ACK: confirm message
+  AA ->> BS: SEND: HELLO
+
+  note over A, AA: 8. notify Alice<br>about connection success
+  AA ->> A: CON: connected
   note over AA: status: ACTIVE/ACTIVE
+
   BS ->> BA: MSG: HELLO: Bob's agent<br>knows Alice can send
   note over BA: status: ACTIVE/ACTIVE
   BA ->> BS: ACK: confirm message
 
-  note over A, B: 8. notify users about connection success
-  AA ->> A: CON: connected
+  note over BA, B: 9. notify Bob<br>about connection success
   BA ->> B: CON: connected

protocol/diagrams/duplex-messaging/queue-rotation-fast.mmd

@@ -0,0 +1,17 @@
+sequenceDiagram
+  participant A as Alice
+  participant R as Current server<br>that has A's<br>receive queue
+  participant R' as New server<br>that has the new A's<br>receive queue
+  participant S as Server<br>that has A's send queue<br>(B's receive queue)
+  participant B as Bob
+
+  A ->> R': NEW: create new queue<br>(allow SKEY)
+  A ->> S: SEND: QADD (R'): send address<br>of the new queue(s)
+  S ->> B: MSG: QADD (R')
+  B ->> R': SKEY: secure new queue
+  B ->> R': SEND: QTEST
+  R' ->> A: MSG: QTEST
+  A ->> R: DEL: delete the old queue
+  B ->> R': SEND: send messages to the new queue
+  R' ->> A: MSG: receive messages from the new queue
+  

protocol/diagrams/duplex-messaging/queue-rotation.mmd

@@ -0,0 +1,21 @@
+sequenceDiagram
+  participant A as Alice
+  participant R as Current server<br>that has A's<br>receive queue
+  participant R' as New server<br>that has the new A's<br>receive queue
+  participant S as Server<br>that has A's send queue<br>(B's receive queue)
+  participant B as Bob
+
+  A ->> R': NEW: create new queue
+  A ->> S: SEND: QADD (R'): send address<br>of the new queue(s)
+  S ->> B: MSG: QADD (R')
+  B ->> R: SEND: QKEY (R'): sender's key<br>for the new queue(s)
+  R ->> A: MSG: QKEY(R')
+  A ->> R': KEY: secure new queue
+  A ->> S: SEND: QUSE (R'): instruction to use new queue(s)
+  S ->> B: MSG: QUSE (R')
+  B ->> R': SEND: QTEST
+  R' ->> A: MSG: QTEST
+  A ->> R: DEL: delete the old queue
+  B ->> R': SEND: send messages to the new queue
+  R' ->> A: MSG: receive messages from the new queue
+  

protocol/diagrams/notifications/register-token-detailed.mmd

@@ -0,0 +1,30 @@
+sequenceDiagram
+  participant M as mobile app
+  participant C as chat core
+  participant A as agent
+  participant P as push server
+  participant APN as APN
+
+  note over M, APN: get device token
+  M ->> APN: registerForRemoteNotifications()
+  APN ->> M: device token
+
+  note over M, P: register device token with push server
+  M ->> C: /_ntf register <token>
+  C ->> A: registerNtfToken(<token>)
+  A ->> P: TNEW
+  P ->> A: ID (tokenId)
+  A ->> C: registered
+  C ->> M: registered
+
+  note over M, APN: verify device token
+  P ->> APN: E2E encrypted code<br>in background<br>notification
+  APN ->> M: deliver background notification with e2ee verification token
+  M ->> C: /_ntf verify <e2ee code>
+  C ->> A: verifyNtfToken(<e2ee code>)
+  A ->> P: TVFY code
+  P ->> A: OK / ERR
+  A ->> C: verified
+  C ->> M: verified
+
+  note over M, APN: now token ID can be used

protocol/diagrams/notifications/register-token.mmd

@@ -1,30 +1,26 @@
 sequenceDiagram
-  participant M as mobile app
-  participant C as chat core
+  participant C as client app
   participant A as agent
-  participant P as push server
-  participant APN as APN
+  participant P as SimpleX<br>Notification<br>Server
+  participant APN as Apple<br>Push Notifications<br>Server
 
-  note over M, APN: get device token
-  M ->> APN: registerForRemoteNotifications()
-  APN ->> M: device token
+  note over C, APN: get device token
+  C ->> APN: registerForRemoteNotifications()
+  APN ->> C: device token
 
-  note over M, P: register device token with push server
-  M ->> C: /_ntf register <token>
-  C ->> A: registerNtfToken(<token>)
+  note over C, P: register device token with push server
+  C ->> A: registerToken
   A ->> P: TNEW
   P ->> A: ID (tokenId)
   A ->> C: registered
-  C ->> M: registered
 
-  note over M, APN: verify device token
+  note over C, APN: verify device token
   P ->> APN: E2E encrypted code<br>in background<br>notification
-  APN ->> M: deliver background notification with e2ee verification token
-  M ->> C: /_ntf verify <e2ee code>
-  C ->> A: verifyNtfToken(<e2ee code>)
+  APN ->> C: deliver background notification with e2ee verification token
+  C ->> A: verifyToken<br>(<e2ee code>)
   A ->> P: TVFY code
   P ->> A: OK / ERR
   A ->> C: verified
-  C ->> M: verified
 
-  note over M, APN: now token ID can be used
+  note over C, APN: now token ID can be used
+  

protocol/diagrams/notifications/subscription-detailed.mmd

@@ -0,0 +1,40 @@
+sequenceDiagram
+  participant M as mobile app
+  participant C as chat core
+  participant A as agent
+  participant S as SMP server
+  participant N as NTF server
+  participant APN as APN
+
+  note over M, APN: register subscription
+
+  alt register existing
+    M -->> A: on /_ntf register, for subscribed queues
+  else create new connection
+    A -->> S: NEW / JOIN
+    note over A, S: ...<br>Connection handshake<br>...
+    S -->> A: CON
+  end
+  A ->> S: NKEY nKey
+  S ->> A: NID nId
+  A ->> N: SNEW tknId dhKey (smpServer, nId, nKey)
+  N ->> A: ID subId dhKey
+  N ->> S: NSUB nId
+  S ->> N: OK [/ NMSG]
+
+  note over M, APN: notify about message
+
+  S ->> N: NMSG
+  N ->> APN: APNSMutableContent<br>ntfQueue, nonce
+  APN ->> M: UNMutableNotificationContent
+  note over M, S: ...<br>Client awaken, message is received<br>...
+  S ->> M: message
+  note over M: mutate notification
+
+  note over M, APN: change APN token
+
+  APN ->> M: new device token
+  M -->> C: /_ntf_sub update tkn
+  C -->> A: updateNtfToken()
+  A -->> N: TUPD tknId newDeviceToken
+  note over M, N: ...<br>Verify token<br>...

protocol/diagrams/notifications/subscription.mmd

@@ -1,17 +1,16 @@
 sequenceDiagram
-  participant M as mobile app
-  participant C as chat core
+  participant C as client app
   participant A as agent
   participant S as SMP server
   participant N as NTF server
   participant APN as APN
 
-  note over M, APN: register subscription
+  note over C, APN: register subscription
 
   alt register existing
-    M -->> A: on /_ntf register, for subscribed queues
+    C -->> A: registerToken
   else create new connection
-    A -->> S: NEW / JOIN
+    A -->> S: create/joinConnection
     note over A, S: ...<br>Connection handshake<br>...
     S -->> A: CON
   end
@@ -20,21 +19,20 @@ sequenceDiagram
   A ->> N: SNEW tknId dhKey (smpServer, nId, nKey)
   N ->> A: ID subId dhKey
   N ->> S: NSUB nId
-  S ->> N: OK [/ NMSG]
+  S ->> N: OK / NMSG:<br>confirm subscription
 
-  note over M, APN: notify about message
+  note over C, APN: notify about message
 
   S ->> N: NMSG
   N ->> APN: APNSMutableContent<br>ntfQueue, nonce
-  APN ->> M: UNMutableNotificationContent
-  note over M, S: ...<br>Client awaken, message is received<br>...
-  S ->> M: message
-  note over M: mutate notification
+  APN ->> C: UNMutableNotificationContent
+  note over C, S: ...<br>Client awaken, message is received<br>...
+  S ->> C: message
+  note over C: show notification
 
-  note over M, APN: change APN token
+  note over C, APN: change APN token
 
-  APN ->> M: new device token
-  M -->> C: /_ntf_sub update tkn
-  C -->> A: updateNtfToken()
+  APN ->> C: new device token
+  C -->> A: updateToken()
   A -->> N: TUPD tknId newDeviceToken
-  note over M, N: ...<br>Verify token<br>...
+  note over C, N: ...<br>Verify token<br>...

protocol/diagrams/simplex-messaging/simplex-creating-fast.mmd

@@ -0,0 +1,23 @@
+sequenceDiagram
+  participant B as Bob (sender)
+  participant S as server (queue RID)
+  participant A as Alice (recipient)
+
+  note over A: creating queue<br>("public" key RK<br>for msg retrieval)
+  A ->> S: 1. create queue ("NEW")
+  S ->> A: respond with queue RID and SID ("IDS")
+
+  note over A: out-of-band msg<br>(sender's queue SID<br>and "public" key EK<br>to encrypt msgs)
+  A -->> B: 2. send out-of-band message
+
+  note over B: secure queue<br>(with "public" key SK for<br>sending messages)
+  B ->> S: 3. confirm queue ("SKEY" command authorized with SK)
+
+  note over B: confirm queue<br>(public key<br>for e2e encryption<br>and any optional<br>encrypted info.)
+  B ->> S: 4. confirm queue ("SEND" command authorized with SK)
+
+  S ->> A: 5. deliver Bob's message (MSG)
+  note over A: decrypt message<br>("private" key EK)
+  A ->> S: acknowledge message (ACK)
+
+  note over S: 6. simplex<br>queue RID<br>is ready to use!

protocol/diagrams/simplex-messaging/simplex-creating.mmd

@@ -10,11 +10,13 @@ sequenceDiagram
   note over A: out-of-band msg<br>(sender's queue SID<br>and "public" key EK<br>to encrypt msgs)
   A -->> B: 2. send out-of-band message
 
-  note over B: confirm queue<br>("public" key SK for<br>sending messages<br>and any optional<br>info encrypted with<br>"public" key EK)
+  note over B: confirm queue<br>("public" key SK for<br>sending messages,<br>public key for<br>e2e encryption<br>and any optional<br>encrypted info)
   B ->> S: 3. confirm queue ("SEND" command not signed)
 
-  S ->> A: 4. deliver Bob's message
+  S ->> A: 4. deliver Bob's message (MSG)
   note over A: decrypt message<br>("private" key EK)
+  A ->> S: acknowledge message (ACK)
+
   A ->> S: 5. secure queue ("KEY", RK-signed)
 
   note over S: 6. simplex<br>queue RID<br>is ready to use!

protocol/diagrams/xftp/xftp-receiving-file.mmd

@@ -0,0 +1,18 @@
+sequenceDiagram
+  participant B as Bob (recipient)
+  participant S as XFTP server(s)
+
+  note over B: having received file description<br>from sender
+
+  loop for each chunk
+    B ->> S: 1a. download chunk ("FGET")
+    S ->> B: send chunk body ("FILE")
+
+    opt
+      B ->> S: 1b. acknowledge chunk reception ("FACK")
+      note over S: delete recipient ID
+      S ->> B: respond with ok ("OK")
+    end
+  end
+
+  note over B: 2. combine chunks into a file<br>3. decrypt file using key from file description<br>4. extract file name and unpad the file<br>5. validate file digest with the file description

protocol/diagrams/xftp/xftp-sending-file.mmd

@@ -0,0 +1,23 @@
+sequenceDiagram
+  participant A as Alice (sender)
+  participant S as XFTP server(s)
+  participant B as recipient(s)
+
+  note over A: 1. prepare file:<br>encrypt,<br>split into chunks,<br>generate recipient<br>keys, etc.
+
+  loop for each chunk
+    A ->> S: 2a. register chunk ("FNEW")
+    S ->> A: respond with sender's and recipients' chunk IDs ("SIDS")
+
+    opt
+      A ->> S: 2b. request additional recipient IDs ("FADD")
+      S ->> A: respond with added recipients' chunk IDs ("RIDS")
+    end
+
+    A ->> S: 2c. upload chunk to chosen server ("FPUT")
+    S ->> A: respond with ok ("OK")
+  end
+
+  note over A: 3. prepare file description(s)
+
+  A -->> B: 4. send file description(s) out-of-band

protocol/diagrams/xrcp/session.mmd

@@ -0,0 +1,44 @@
+sequenceDiagram
+  participant CI as Controller UI
+  participant CC as Controller Core
+  participant HC as Host Core
+  participant HI as Host UI
+
+note over CI, HI: 1. Session invitation
+CI->>CC: "Link a mobile"
+CC-->>CI: Session invitation URI
+note over CC: Listen for TCP connection
+activate CC
+HI->>HC: Session invitation URI
+
+note over CI, HI: 2. Establishing TLS connection
+HC-->>CC: TCP connect
+note over CC, HC: TLS handshake
+par
+    note over CC: validate client X509 credentials
+    CC->>CI: session code from tlsUnique
+    CI-->>CC: user confirmation
+and
+    note over HC: validate server X509 credentials
+    HC->>HI: session code from tlsUnique
+    HI-->>HC: user confirmation
+end
+
+note over CI, HI: 3. Session verification and protocol negotiation
+HC->>CC: host HELLO
+note over CC: validate version, CA fingerprint
+alt
+    CC-->>HC: controller ERROR
+else
+    CC-->>HC: controller HELLO
+    note over CC, HC: update stored keys
+end
+deactivate CC
+
+note over CI, HI: 4. Session operation
+loop
+    CI->>CC: command
+    CC->>HC: XRCP command
+    HC-->>CC: XRCP response
+    CC-->>CI: response
+end

protocol/overview-tjr.md

@@ -1,4 +1,4 @@
-Revision 1, 2022-01-01
+Revision 2, 2024-06-22
 
 Evgeny Poberezkin
 
@@ -13,19 +13,23 @@ Evgeny Poberezkin
 - [Technical Details](#technical-details)
   - [Trust in Servers](#trust-in-servers)
   - [Client -> Server Communication](#client---server-communication)
+  - [2-hop Onion Message Routing](#2-hop-onion-message-routing)
   - [SimpleX Messaging Protocol](#simplex-messaging-protocol)
   - [SimpleX Agents](#simplex-agents)
   - [Encryption Primitives Used](#encryption-primitives-used)
 - [Threat model](#threat-model)
 - [Acknowledgements](#acknowledgements)
 
+
 ## Introduction
 
 #### What is SimpleX
 
 SimpleX as a whole is a platform upon which applications can be built. [SimpleX Chat](https://github.com/simplex-chat/simplex-chat) is one such application that also serves as an example and reference application.
 
- - [SimpleX Messaging Protocol](https://github.com/simplex-chat/simplexmq/blob/master/protocol/simplex-messaging.md) (SMP) is a protocol to send messages in one direction to a recipient, relying on a server in-between. The messages are delivered via uni-directional queues created by recipients.
+ - [SimpleX Messaging Protocol](./simplex-messaging.md) (SMP) is a protocol to send messages in one direction to a recipient, relying on a server in-between. The messages are delivered via uni-directional queues created by recipients.
+ 
+ - SMP protocol allows to send message via a SMP server playing proxy role using 2-hop onion routing (referred to as "private routing" in messaging clients) to protect transport information of the sender (IP address and session) from the server chosen (and possibly controlled) by the recipient.
 
  - SMP runs over a transport protocol (shown below as TLS) that provides integrity, server authentication, confidentiality, and transport channel binding.
 
@@ -35,7 +39,9 @@ SimpleX as a whole is a platform upon which applications can be built. [SimpleX
 
  - SimpleX Client libraries speak SMP to SimpleX Servers and provide a low-level API not generally intended to be used by applications.
 
- - SimpleX Agents interface with SimpleX Clients to provide a more high-level API intended to be used by applications. Typically they are embedded as libraries, but are designed so they can also be abstracted into local services.
+ - SimpleX Agents interface with SimpleX Clients to provide a more high-level API intended to be used by applications. Typically they are embedded as libraries, but can also be abstracted into local services.
+
+ - SimpleX Agents communicate with other agents inside e2e encrypted envelopes provided by SMP protocol - the syntax and semantics of the messages exchanged by the agent are defined by [SMP agent protocol](./agent-protocol.md)
 
 
 *Diagram showing the SimpleX Chat app, with logical layers of the chat application interfacing with a SimpleX Agent library, which in turn interfaces with a SimpleX Client library. The Client library in turn speaks the Messaging Protocol to a SimpleX Server.*
@@ -72,10 +78,11 @@ SimpleX as a whole is a platform upon which applications can be built. [SimpleX
 
    - Low latency: the delay introduced by the network should not be higher than 100ms-1s in addition to the underlying TCP network latency.
 
-2. Provide better communication security and privacy than the alternative instant messaging solutions.  In particular SimpleX provides better privacy of metadata (who talks to whom and when) and better security against active network attackers and malicious servers.
+2. Provide better communication security and privacy than the alternative instant messaging solutions. In particular SimpleX provides better privacy of metadata (who talks to whom and when) and better security against active network attackers and malicious servers.
 
 3. Balance user experience with privacy requirements, prioritizing experience of mobile device users.
 
+
 #### In Comparison
 
 SimpleX network has a design similar to P2P networks, but unlike most P2P networks it consists of clients and servers without depending on any centralized component.
@@ -91,53 +98,73 @@ In comparison to more traditional messaging applications (e.g. WhatsApp, Signal,
 
 - users can change servers with minimal disruption - even after an in-use server disappears, simply by changing the configuration on which servers the new queues are created.
 
+
 ## Technical Details
 
 #### Trust in Servers
 
 Clients communicate directly with servers (but not with other clients) using SimpleX Messaging Protocol (SMP) running over some transport protocol that provides integrity, server authentication, confidentiality, and transport channel binding. By default, we assume this transport protocol is TLS.
 
-Users use multiple servers, and choose where to receive their messages. Accordingly, they send messages to their communication partners' chosen servers.
+Users use multiple servers, and choose where to receive their messages. Accordingly, they send messages to their communication partners' chosen servers either directly, if this is a known/trusted server, or via another SMP server providing proxy functionality to protect IP address and session of the sender.
 
-Although end-to-end encryption is always present, users place a degree of trust in servers. This trust decision is very similar to a user's choice of email provider; however the trust placed in a SimpleX server is significantly less. Notably, there is no re-used identifier or credential between queues on the same (or different) servers. While a user *may* re-use a connection to fetch from multiple queues, or connect to a server from the same IP address, both are choices a user may opt into to break the promise of un-correlatable queues.
+Although end-to-end encryption is always present, users place a degree of trust in servers they connect to. This trust decision is very similar to a user's choice of email provider; however the trust placed in a SimpleX server is significantly less. Notably, there is no re-used identifier or credential between queues on the same (or different) servers. While a user *may* re-use a transport connection to fetch messages from multiple queues, or connect to a server from the same IP address, both are choices a user may opt into to break the promise of un-correlatable queues.
 
 Users may trust a server because:
 
-- They deploy and control the servers themselves from the available open-source code. This has the trade-offs of strong trust in the server but limited metadata obfuscation to a passive network observer. Techniques such as noise traffic, traffic mixing (incurring latency), and using an onion routing transport protocol can mitigate that latter.
+- They deploy and control the servers themselves from the available open-source code. This has the trade-offs of strong trust in the server but limited metadata obfuscation to a passive network observer. Techniques such as noise traffic, traffic mixing (incurring latency), and using an onion routing transport protocol can mitigate that.
 
 - They use servers from a trusted commercial provider. The more clients the provider has, the less metadata about the communication times is leaked to the network observers.
 
-- Users trust their contacts and the servers they chose.
+By default, servers do not retain access logs, and permanently delete messages and queues when requested. Messages persist only in memory until they cross a threshold of time, typically on the order of days.[0] There is still a risk that a server maliciously records all queues and messages (even though encrypted) sent via the same transport connection to gain a partial knowledge of the user’s communications graph and other meta-data.
 
-By default, servers do not retain access logs, and permanently delete messages and queues when requested.  Messages persist only in memory until they cross a threshold of time, typically on the order of days.[0] There is still a risk that a server maliciously records all queues and messages (even though encrypted) sent via the same transport connection to gain a partial knowledge of the user’s communications graph and other meta-data.
+SimpleX supports measures (managed transparently to the user at the agent level) to mitigate the trust placed in servers.  These include rotating the queues in use between users, noise traffic, supporting overlay networks such as Tor, and isolating traffic to different queues to different transport connections (and Tor circuits, if Tor is used).
 
-SimpleX supports measures (managed transparently to the user at the agent level) to mitigate the trust placed in servers.  These include rotating the queues in use between users, noise traffic, and supporting overlay networks such as Tor.
-
-[0] While configurable by servers, a minimum value is enforced by the default software. SimpleX Agents provide redundant routing over queues to mitigate against message loss.
+[0] While configurable by servers, a minimum value is enforced by the default software. SimpleX Agents can provide redundant routing over queues to mitigate against message loss.
 
 
 #### Client -> Server Communication
 
 Utilizing TLS grants the SimpleX Messaging Protocol (SMP) server authentication and metadata protection to a passive network observer. But SMP does not rely on the transport protocol for message confidentiality or client authentication. The SMP protocol itself provides end-to-end confidentiality, authentication, and integrity of messages between communicating parties.
 
-Servers have long-lived, self-signed, offline certificates whose hash is pre-shared with clients over secure channels - either provided with the client library or provided in the secure introduction between clients.  The offline certificate signs an online certificate used in the transport protocol handshake. [0]
+Servers have long-lived, self-signed, offline certificates whose hash is pre-shared with clients over secure channels - either provided with the client library or provided in the secure introduction between clients, as part of the server address.  The offline certificate signs an online certificate used in the transport protocol handshake. [0]
 
 If the transport protocol's confidentiality is broken, incoming and outgoing messages to the server cannot be correlated by message contents. Additionally, because of encryption at the SMP layer, impersonating the server is not sufficient to pass (and therefore correlate) a message from a sender to recipient - the only attack possible is to drop the messages. Only by additionally *compromising* the server can one pass and correlate messages.
 
 It's important to note that the SMP protocol does not do server authentication. Instead we rely upon the fact that an attacker who tricks the transport protocol into authenticating the server incorrectly cannot do anything with the SMP messages except drop them.
 
-After the connection is established, the client sends blocks of a fixed size 16Kb, and the server replies with the blocks of the same size to reduce metadata observable to a network adversary. The protocol has been designed to make traffic correlation attacks difficult, adapting ideas from Tor, remailers, and more general onion and mix networks. It does not try to replace Tor though - SimpleX servers can be deployed as onion services and SimpleX clients can communicate with servers over Tor to further improve participants privacy.
+After the connection is established, the client sends blocks of a fixed size 16KB, and the server replies with the blocks of the same size to reduce metadata observable to a network adversary. The protocol has been designed to make traffic correlation attacks difficult, adapting ideas from Tor, remailers, and more general onion and mix networks. It does not try to replace Tor though - SimpleX servers can be deployed as onion services and SimpleX clients can communicate with servers over Tor to further improve participants privacy.
 
-By using fixed-size blocks, oversized for the expected content, the vast majority of traffic is uniform in nature. When enough traffic is transiting a server simultaneously, the server acts as a (very) low-latency mix node.  We can't rely on this behavior to make a security claim, but we have engineered to take advantage of it when we can. As mentioned, this holds true even if the transport connection is compromised.
+By using fixed-size blocks, oversized for the expected content, the vast majority of traffic is uniform in nature. When enough traffic is transiting a server simultaneously, the server acts as a low-latency mix node. We can't rely on this behavior to make a security claim, but we have engineered to take advantage of it when we can. As mentioned, this holds true even if the transport connection is compromised.
 
-The protocol does not protect against attacks targeted at particular users with known identities - e.g., if the attacker wants to prove that two known users are communicating, they can achieve it. At the same time, it substantially complicates large-scale traffic correlation, making determining the real user identities much less effective.
+The protocol does not protect against attacks targeted at particular users with known identities - e.g., if the attacker wants to prove that two known users are communicating, they can achieve it by observing their local traffic. At the same time, it substantially complicates large-scale traffic correlation, making determining the real user identities much less effective.
 
 [0] Future versions of SMP may add support for revocation lists of certificates, presently this risk is mitigated by the SMP protocol itself.
 
 
+#### 2-hop Onion Message Routing
+
+As SimpleX Messaging Protocol servers providing messaging queues are chosen by the recipients, in case senders connect to these servers directly the server owners (who potentially can be the recipients themselves) can learn senders' IP addresses (if Tor is not used) and which other queues on the same server are accessed by the user in the same transport connection (even if Tor is used).
+
+While the clients support isolating the messages sent to different queues into different transport connections (and Tor circuits), this is not practical, as it consumes additional traffic and system resources.
+
+To mitigate this problem SimpleX Messaging Protocol servers support 2-hop onion message routing when the SMP server chosen by the sender forwards the messages to the servers chosen by the recipients, thus protecting both the senders IP addresses and sessions, even if connection isolation and Tor are not used.
+
+The design of 2-hop onion message routing prevents these potential attacks:
+
+- MITM by proxy (SMP server that forwards the messages).
+
+- Identification by the proxy which and how many queues the sender sends messages to (as messages are additionally e2e encrypted between the sender and the destination SMP server).
+
+- Correlation of messages sent to different queues via the same user session (as random correlation IDs and keys are used for each message).
+
+See more details about 2-hop onion message routing design in [SimpleX Messaging Protocol](./simplex-messaging.md#proxying-sender-commands)
+
+Also see [Threat model](#threat-model)
+
+
 #### SimpleX Messaging Protocol
 
-SMP is initialized with an in-person or out-of-band introduction message, where Alice provides Bob with details of a server (including IP, port, and hash of the long-lived offline certificate), a queue ID, and Alice's public key for her receiving queue. These introductions are similar to the PANDA key-exchange, in that if observed, the adversary can race to establish the communication channel instead of the intended participant. [0]
+SMP is initialized with an in-person or out-of-band introduction message, where Alice provides Bob with details of a server (including IP address or host name, port, and hash of the long-lived offline certificate), a queue ID, and Alice's public keys to agree e2e encryption. These introductions are similar to the PANDA key-exchange, in that if observed, the adversary can race to establish the communication channel instead of the intended participant. [0]
 
 Because queues are uni-directional, Bob provides an identically-formatted introduction message to Alice over Alice's now-established receiving queue.
 
@@ -145,6 +172,7 @@ When setting up a queue, the server will create separate sender and recipient qu
 
 [0] Users can additionally create public 'contact queues' that are only used to receive connection requests.  
 
+
 #### SimpleX Agents
 
 SimpleX agents provide higher-level operations compared to SimpleX Clients, who are primarily concerned with creating queues and communicating with servers using SMP.  Agent operations include:
@@ -157,9 +185,10 @@ SimpleX agents provide higher-level operations compared to SimpleX Clients, who
 
 - Noise traffic
 
+
 #### Encryption Primitives Used
 
-- Ed448 to sign/verify commands to SMP servers (Ed25519 is also supported via client/server configuration).
+- Ed25519 or Curve25519 to authorize/verify commands to SMP servers (authorization algorithm is set via client/server configuration).
 - Curve25519 for DH exchange to agree:
   - the shared secret between server and recipient (to encrypt message bodies - it avoids shared cipher-text in sender and recipient traffic)
   - the shared secret between sender and recipient (to encrypt messages end-to-end in each queue - it avoids shared cipher-text in redundant queues).
@@ -170,42 +199,44 @@ SimpleX agents provide higher-level operations compared to SimpleX Clients, who
   - AES-GCM AEAD cipher,
   - SHA512-based HKDF for key derivation.
 
+
 ## Threat Model
 
 #### Global Assumptions
 
- - A user protects their local database and key material
- - The user's application is authentic, and no local malware is running
- - The cryptographic primitives in use are not broken
+ - A user protects their local database and key material.
+ - The user's application is authentic, and no local malware is running.
+ - The cryptographic primitives in use are not broken.
  - A user's choice of servers is not directly tied to their identity or otherwise represents distinguishing information about the user.
+ - The user's client uses 2-hop onion message routing.
 
 #### A passive adversary able to monitor the traffic of one user
 
 *can:*
 
- - identify that and when a user is using SimpleX
+ - identify that and when a user is using SimpleX.
 
- - block SimpleX traffic
-
- - determine which servers the user communicates with
+ - determine which servers the user receives the messages from.
 
  - observe how much traffic is being sent, and make guesses as to its purpose.
 
 *cannot:*
 
- - see who sends messages to the user and who the user sends the messages to
+ - see who sends messages to the user and who the user sends the messages to.
+
+ - determine the servers used by users' contacts.
 
 #### A passive adversary able to monitor a set of senders and recipients
 
  *can:*
 
- - identify who and when is using SimpleX
+ - identify who and when is using SimpleX.
 
- - learn which SimpleX Messaging Protocol servers are used as receive queues for which users
+ - learn which SimpleX Messaging Protocol servers are used as receive queues for which users.
 
- - learn when messages are sent and received
+ - learn when messages are sent and received.
 
- - perform traffic correlation attacks against senders and recipients and correlate senders and recipients within the monitored set, frustrated by the number of users on the servers
+ - perform traffic correlation attacks against senders and recipients and correlate senders and recipients within the monitored set, frustrated by the number of users on the servers.
 
  - observe how much traffic is being sent, and make guesses as to its purpose
 
@@ -217,43 +248,83 @@ SimpleX agents provide higher-level operations compared to SimpleX Clients, who
 
 *can:*
 
-- learn when a queue recipient or sender is online
+- learn when a queue recipient is online
 
-- know how many messages are sent via the queue (although some may be noise)
+- know how many messages are sent via the queue (although some may be noise or not content messages).
 
-- perform queue correlation (matching multiple queues to a single user) via either a re-used transport connection, user's IP Address, or connection timing regularities
+- learn which messages would trigger notifications even if a user does not use [push notifications](./push-notifications.md).
 
-- learn a user's IP address, track them through other IP addresses they use to access the same queue, and infer information (e.g. employer) based on the IP addresses, as long as Tor is not used.
+- perform the correlation of the queue used to receive messages (matching multiple queues to a single user) via either a re-used transport connection, user's IP Address, or connection timing regularities.
 
-- drop all future messages inserted into a queue, detectable only over other, redundant queues
+- learn a recipient's IP address, track them through other IP addresses they use to access the same queue, and infer information (e.g. employer) based on the IP addresses, as long as Tor is not used.
+
+- drop all future messages inserted into a queue, detectable only over other, redundant queues.
 
 - lie about the state of a queue to the recipient and/or to the sender  (e.g. suspended or deleted when it is not).
 
-- spam a user with invalid messages
+- spam a user with invalid messages.
 
 *cannot:*
 
-- undetectably add, duplicate, or corrupt individual messages
+- undetectably add, duplicate, or corrupt individual messages.
 
-- undetectably drop individual messages, so long as a subsequent message is delivered
+- undetectably drop individual messages, so long as a subsequent message is delivered.
 
-- learn the contents of messages
+- learn the contents or type of messages.
 
-- distinguish noise messages from regular messages except via timing regularities
+- distinguish noise messages from regular messages except via timing regularities.
 
-- compromise the user's end-to-end encryption with an active attack
+- compromise the users' end-to-end encryption with an active attack.
+
+- learn a sender's IP address, track them through other IP addresses they use to access the same queue, and infer information (e.g. employer) based on the IP addresses, even if Tor is not used (provided messages are sent via proxy SMP server).
+
+- perform senders' queue correlation (matching multiple queues to a single sender) via either a re-used transport connection, user's IP Address, or connection timing regularities, unless it has additional information from the proxy SMP server (provided messages are sent via proxy SMP server).
+
+#### SimpleX Messaging Protocol server that proxies the messages to another SMP server
+
+*can:*
+
+- learn a sender's IP address, as long as Tor is not used.
+
+- learn when a sender with a given IP address is online.
+
+- know how many messages are sent from a given IP address and to a given destination SMP server.
+
+- drop all messages from a given IP address or to a given destination server.
+
+- unless destination SMP server detects repeated public DH keys of senders, replay messages to a destination server within a single session, causing either duplicate message delivery (which will be detected and ignored by the receiving clients), or, when receiving client is not connected to SMP server, exhausting capacity of destination queues used within the session.
+
+*cannot:*
+
+- perform queue correlation (matching multiple queues to a single user), unless it has additional information from the destination SMP server.
+
+- undetectably add, duplicate, or corrupt individual messages.
+
+- undetectably drop individual messages, so long as a subsequent message is delivered.
+
+- learn the contents or type of messages.
+
+- learn which messages would trigger notifications.
+
+- learn the destination queues of messages.
+
+- distinguish noise messages from regular messages except via timing regularities.
+
+- compromise the user's end-to-end encryption with another user via an active attack.
+
+- compromise the user's end-to-end encryption with the destination SMP servers via an active attack.
 
 #### An attacker who obtained Alice's (decrypted) chat database
 
 *can:*
 
-- see the history of all messages exchanged by Alice with her communication partners
+- see the history of all messages exchanged by Alice with her communication partners.
 
-- see shared profiles of contacts and groups
+- see shared profiles of contacts and groups.
 
-- surreptitiously receive new messages sent to Alice via existing queues; until communication queues are rotated or the Double-Ratchet advances forward
+- surreptitiously receive new messages sent to Alice via existing queues; until communication queues are rotated or the Double-Ratchet advances forward.
 
-- prevent Alice from receiving all new messages sent to her - either surreptitiously by emptying the queues regularly or overtly by deleting them
+- prevent Alice from receiving all new messages sent to her - either surreptitiously by emptying the queues regularly or overtly by deleting them.
 
 - send messages from the user to their contacts; recipients will detect it as soon as the user sends the next message, because the previous message hash won’t match (and potentially won’t be able to decrypt them in case they don’t keep the previous ratchet keys).
 
@@ -269,41 +340,41 @@ SimpleX agents provide higher-level operations compared to SimpleX Clients, who
 
 *can:*
 
-- spam the user with messages
+- spam the user with messages.
 
-- forever retain messages from the user
+- forever retain messages from the user.
 
 *cannot:*
 
-- cryptographically prove to a third-party that a message came from a user (assuming the user’s device is not seized)
+- cryptographically prove to a third-party that a message came from a user (assuming the user’s device is not seized).
 
-- prove that two contacts they have is the same user
+- prove that two contacts they have is the same user.
 
-- cannot collaborate with another of the user's contacts to confirm they are communicating with the same user
+- cannot collaborate with another of the user's contacts to confirm they are communicating with the same user.
 
 #### An attacker who observes Alice showing an introduction message to Bob
 
 *can:*
 
- - Impersonate Bob to Alice
+ - Impersonate Bob to Alice.
 
 *cannot:*
 
- - Impersonate Alice to Bob
+ - Impersonate Alice to Bob.
 
 #### An attacker with Internet access
 
 *can:*
 
-- Denial of Service SimpleX messaging servers
+- Denial of Service SimpleX messaging servers.
 
-- spam a user's public “contact queue” with connection requests
+- spam a user's public “contact queue” with connection requests.
 
 *cannot:*
 
-- send messages to a user who they are not connected with
+- send messages to a user who they are not connected with.
 
-- enumerate queues on a SimpleX server
+- enumerate queues on a SimpleX server.
 
 
 ## Acknowledgements

protocol/pqdr.md

@@ -0,0 +1,222 @@
+Version 1, 2024-06-22
+
+# Post-quantum resistant augmented double ratchet algorithm (PQDR)
+
+## Table of contents
+
+- [Overview](#overview)
+- [Comparison with the other approaches](#comparison-with-the-other-approaches)
+  - [PQXDH for post-quantum key agreement](#pqxdh-for-post-quantum-key-agreement) (Signal)
+  - [Hybrid Signal protocol for post-quantum encryption](#hybrid-signal-protocol-for-post-quantum-encryption) (Tutanota)
+- [Augmented double ratchet algorithm](#augmented-double-ratchet-algorithm)
+- [Double ratchet with encrypted headers augmented with double PQ KEM](#double-ratchet-with-encrypted-headers-augmented-with-double-pq-kem)
+  - [Initialization](#initialization)
+  - [Encrypting messages](#encrypting-messages)
+  - [Decrypting messages](#decrypting-messages)
+- [Implementation considerations](#implementation-considerations)
+- [Chosen KEM algorithm](#chosen-kem-algorithm)
+- [Summary](#summary)
+
+## Overview
+
+It is a reasonable assumption that "record-now-decrypt-later" attacks are ongoing, so the users want to use cryptographic schemes for end-to-end encryption that are augmented with some post-quantum algorithm that is believed to be resistant to quantum computers.
+
+SimpleX Chat uses [double-ratchet with header encryption](https://signal.org/docs/specifications/doubleratchet/#double-ratchet-with-header-encryption) to provide end-to-end encryption to messages and files. This document describes augmented algorithm with post-quantum key encapsulation mechanism (KEM) making it resistant to quantum computers.
+
+Double-ratchet algorithm is a state of the art solution for end to end encryption offering a set of qualities that is not present in any other algorithm:
+
+- perfect forward secrecy, i.e. compromise of session or long term keys does not lead to the ability to decrypt any of the past messages.
+- deniability (also known as repudiation), i.e. the fact that the recipient of the message while having the proof of message authenticity, cannot prove to a third party that the sender actually sent this message.
+- break-in recovery (also know as post-compromise security or future secrecy), i.e. the ability of the end-to-end encryption security to recover from the compromise of the long term keys. This is achieved by generating a new random key pair whenever a new DH key is received (DH ratchet step).
+
+It is desirable to preserve all these qualities when augmenting the algorithm with a post-quantum algorithm, and having these qualities resistant to both conventional and quantum computers.
+
+## Comparison with the other approaches
+
+### PQXDH for post-quantum key agreement
+
+[The solution](https://signal.org/docs/specifications/pqxdh/) recently [introduced by Signal](https://signal.org/blog/pqxdh/) augments the initial key agreement ([X3DH](https://signal.org/docs/specifications/x3dh/)) that is made prior to double ratchet algorithm. This is believed to provide protection from "record-now-decrypt-later" attack, but if the attacker at any point obtains long term keys from any of the devices, the break-in recovery will not be post-quantum resistant, and the attacker with quantum computer will be able to decrypt all the subsequent messages.
+
+### Hybrid Signal protocol for post-quantum encryption
+
+[The solution](https://eprint.iacr.org/2021/875.pdf) [proposed by Tutanota](https://tutanota.com/blog/posts/pqmail-update/) aims to preserve the break-in recovery property of double ratchet, but in doing so it:
+- replaces rather than augments DH key agreement with post-quantum KEM mechanism, making it potentially vulnerable to conventional computers.
+- adds signature to the DH ratchet step, to compensate for not keeping DH key agreement, but losing the deniability property for some of the messages.
+
+## Augmented double ratchet algorithm
+
+The double ratchet algorithm is augmented with post-quantum KEM mechanism, preserving all properties of the double ratchet algorithm.
+
+It is possible, because although double ratchet uses DH (which is a non-interactive key exchanges), it uses it "interactively", when the new DH keys are generated by both parties in turns. Parties of double-ratchet encrypted communication can run two post-quantum key encapsulation mechanisms in parallel with both DH and KEM key agreements in each DH ratchet step, making break-in recovery of double ratchet algorithm post-quantum resistant, without losing deniability or resistance to conventional computers.
+
+Specifically, [double ratchet with encrypted headers](https://signal.org/docs/specifications/doubleratchet/#double-ratchet-with-header-encryption) is augmented with some post-quantum key encapsulation mechanism (KEM) as described below. A possible algorithm for PQ KEM is [NTRU-prime](https://ntruprime.cr.yp.to), that is currently adopted in SSH and has available implementations. It is important though that the proposed scheme can be used with any PQ KEM algorithm.
+
+The downside of the scheme is its substantial size overhead, as the encapsulation key and encapsulated shared secret are added to the header of each message. For the algorithm described below NTRU-prime adds ~2-4kb to each message (depending on the key size and the chosen variant). See [this table](https://ntruprime.cr.yp.to/security.html) for key and ciphertext sizes and the assessment of the security level for various key sizes.
+
+It is possible to reduce size overhead by using only one KEM agreement and making only one of two ratchet steps providing post-quantum resistant break-in recovery.
+
+## Double ratchet with encrypted headers augmented with double PQ KEM
+
+Algorithm below assumes that in addition to shared secret from the initial key agreement, there will be an encapsulation key available from the party that published its keys (Bob).
+
+### Initialization
+
+The double ratchet initialization is defined in pseudo-code. This pseudo-code is identical to Signal algorithm specification except for that parts that add post-quantum key agreement.
+
+```
+// Alice obtained Bob's keys and initializes ratchet first
+def RatchetInitAlicePQ2HE(state, SK, bob_dh_public_key, shared_hka, shared_nhkb, bob_pq_kem_encapsulation_key):
+    state.DHRs = GENERATE_DH()
+    state.DHRr = bob_dh_public_key
+    // below added for post-quantum KEM
+    state.PQRs = GENERATE_PQKEM()
+    state.PQRr = bob_pq_kem_encapsulation_key
+    state.PQRss = random // shared secret for KEM
+    state.PQRct = PQKEM-ENC(state.PQRr, state.PQRss) // encapsulated additional shared secret
+    // above added for KEM
+    // the next line augments DH key agreement with PQ shared secret
+    state.RK, state.CKs, state.NHKs = KDF_RK_HE(SK, DH(state.DHRs, state.DHRr) || state.PQRss) 
+    state.CKr = None
+    state.Ns = 0
+    state.Nr = 0
+    state.PN = 0
+    state.MKSKIPPED = {}
+    state.HKs = shared_hka
+    state.HKr = None
+    state.NHKr = shared_nhkb
+
+// Bob initializes ratchet second, having received Alice's connection request
+def RatchetInitBobPQ2HE(state, SK, bob_dh_key_pair, shared_hka, shared_nhkb, bob_pq_kem_key_pair):
+    state.DHRs = bob_dh_key_pair
+    state.DHRr = None
+    // below added for KEM
+    state.PQRs = bob_pq_kem_key_pair
+    state.PQRr = None
+    state.PQRss = None
+    state.PQRct = None
+    // above added for KEM
+    state.RK = SK 
+    state.CKs = None
+    state.CKr = None
+    state.Ns = 0
+    state.Nr = 0
+    state.PN = 0
+    state.MKSKIPPED = {}
+    state.HKs = None
+    state.NHKs = shared_nhkb
+    state.HKr = None
+    state.NHKr = shared_hka
+```
+
+`GENERATE_PQKEM` generates decapsulation/encapsulation key pair.
+
+`PQKEM-ENC` is key encapsulation algorithm.
+
+Other than commented lines, the above adds parameters `bob_pq_kem_encapsulation_key` and `bob_pq_kem_key_pair` to the ratchet initialization. Otherwise it is identical to the original double ratchet initialization.
+
+### Encrypting messages
+
+```
+def RatchetEncryptPQ2HE(state, plaintext, AD):
+    state.CKs, mk = KDF_CK(state.CKs)
+    // encapsulation key from PQRs and encapsulated shared secret is added to header
+    header = HEADER_PQ2(
+      dh = state.DHRs.public,
+      kem = state.PQRs.public, // added for KEM #2
+      ct = state.PQRct // added for KEM #1
+      pn = state.PN,
+      n = state.Ns,
+    )
+    enc_header = HENCRYPT(state.HKs, header)
+    state.Ns += 1
+    return enc_header, ENCRYPT(mk, plaintext, CONCAT(AD, enc_header))
+```
+
+Other than adding encapsulation key and encapsulated shared secret into the header, the above is identical to the original double ratchet message encryption step.
+
+### Decrypting messages
+
+```
+def RatchetDecryptPQ2HE(state, enc_header, ciphertext, AD):
+    plaintext = TrySkippedMessageKeysHE(state, enc_header, ciphertext, AD)
+    if plaintext != None:
+        return plaintext
+    header, dh_ratchet = DecryptHeader(state, enc_header) // DecryptHeader is the same as in double ratchet specification
+    if dh_ratchet:
+        SkipMessageKeysHE(state, header.pn) // SkipMessageKeysHE is the same as in double ratchet specification
+        DHRatchetPQ2HE(state, header)
+    SkipMessageKeysHE(state, header.n)
+    state.CKr, mk = KDF_CK(state.CKr)
+    state.Nr += 1
+    return DECRYPT(mk, ciphertext, CONCAT(AD, enc_header))
+
+// DecryptHeader is the same as in double ratchet specification
+def DecryptHeader(state, enc_header):
+    header = HDECRYPT(state.HKr, enc_header)
+    if header != None:
+        return header, False
+    header = HDECRYPT(state.NHKr, enc_header)
+    if header != None:
+        return header, True
+    raise Error()
+
+def DHRatchetPQ2HE(state, header):
+    state.PN = state.Ns
+    state.Ns = 0
+    state.Nr = 0
+    state.HKs = state.NHKs
+    state.HKr = state.NHKr
+    state.DHRr = header.dh
+    // save new encapsulation key from header
+    state.PQRr = header.kem
+    // decapsulate shared secret from header - KEM #2
+    ss = PQKEM-DEC(state.PQRs.private, header.ct)
+    // use decapsulated shared secret with receiving ratchet
+    state.RK, state.CKr, state.NHKr = KDF_RK_HE(state.RK, DH(state.DHRs, state.DHRr) || ss)
+    state.DHRs = GENERATE_DH()
+    // below is added for KEM
+    state.PQRs = GENERATE_PQKEM() // generate new PQ key pair
+    state.PQRss = random // shared secret for KEM
+    state.PQRct = PQKEM-ENC(state.PQRr, state.PQRss) // encapsulated additional shared secret KEM #1
+    // above is added for KEM
+    // use new shared secret with sending ratchet
+    state.RK, state.CKs, state.NHKs = KDF_RK_HE(state.RK, DH(state.DHRs, state.DHRr) || state.PQRss)
+```
+
+`PQKEM-DEC` is key decapsulation algorithm.
+
+`DHRatchetPQ2HE` augments both DH agreements with decapsulated shared secret from the received header and with the new shared secret, respectively. The new shared secret together with the new encapsulation key are saved in the state and will be added to the header in the next sent message.
+
+Other than augmenting DH key agreements with the shared secrets from KEM, the above is identical to the original double ratchet DH ratchet step.
+
+It is worth noting that while DH agreements work as ping-pong, when the new received DH key is used for both DH agreements (and only the sent DH key is updated for the second DH key agreement), PQ KEM agreements in the proposed scheme work as a "parallel ping-pong", with two balls in play all the time (two KEM agreements run in parallel).
+
+## Implementation considerations for SimpleX Messaging Protocol
+
+As SimpleX Messaging Protocol pads messages to a fixed size, using 16kb transport blocks, the size increase introduced by this scheme can be compensated for by using ZSTD encryption of JSON bodies and image previews encoded as base64. While there may be some rare cases of random texts that would fail to compress, in all real scenarios it would not cause the message size reduction.
+
+Sharing the initial keys in case of SimpleX Chat it is equivalent to sharing the invitation link. As encapsulation key is large, it may be inconvenient to share it in the link in some contexts, e.g. when QR codes are used.
+
+It is possible to postpone sharing the encapsulation key until the first message from Alice (confirmation message in SMP protocol), the party sending connection request. The upside here is that the invitation link size would not increase. The downside is that the user profile shared in this confirmation will not be encrypted with PQ-resistant algorithm.
+
+Another consideration is pairwise ratchets in groups. Key generation in sntrup761 is quite slow - on slow devices it can be as slow as 10-20 keys per second, so using this primitive in groups larger than 10-20 members would result in slow performance.
+
+For backward compatibility the implementation must support adding PQ-resistant key agreement to the existing connections.
+
+It is also beneficial to support removing PQ-resistant key agreement from the connections that have them, e.g. as the group size grows.
+
+### Chosen KEM algorithm
+
+The implementation uses Streamlined NTRU-Prime 761 (sntrup761) that was also used for OpenSSH for a long time.
+
+It was chosen over ML-KEM (Kyber) standardized by NIST for several reasons:
+
+- sntrup761 was used in OpenSSH for a long period of time.
+- ML-KEM standardization process raised [concerns](https://groups.google.com/a/list.nist.gov/g/pqc-forum/c/WFRDl8DqYQ4) [amongst](https://blog.cr.yp.to/20231003-countcorrectly.html) the experts.
+- ML-KEM (if modified) is likely to have conflicts with the existing patents, unlike sntrup761.
+
+It was chosen over non-interactive CTIDH due to its slower implementation, and lack of optimized code for aarch64 CPUs used in mobile devices.
+
+## Summary
+
+If chosen PQ KEM proves secure against quantum computer attacks, then the proposed augmented double ratchet will also be secure against quantum computer attack, including break-in recovery property, while keeping deniability and forward secrecy, because the [same proof](https://eprint.iacr.org/2016/1013.pdf) as for double ratchet algorithm would hold here, provided chosen KEM is secure.

protocol/push-notifications.md

@@ -0,0 +1,398 @@
+Version 2, 2024-06-22
+
+# Overview of push notifications for SimpleX Messaging Servers
+
+## Table of contents
+
+- [Introduction](#introduction)
+- [Participating servers](#participating-servers)
+- [Register device token to receive push notifications](#register-device-token-to-receive-push-notifications)
+- [Subscribe to connection notifications](#subscribe-to-connection-notifications)
+- [SimpleX Notification Server protocol](#simplex-notification-server-protocol)
+  - [Register new notification token](#register-new-notification-token)
+  - [Verify notification token](#verify-notification-token)
+  - [Check notification token status](#check-notification-token-status)
+  - [Replace notification token](#replace-notification-token)
+  - [Delete notification token](#delete-notification-token)
+  - [Subscribe to periodic notifications](#subscribe-to-periodic-notifications)
+  - [Create SMP message notification subscription](#create-smp-message-notification-subscription)
+  - [Check notification subscription status](#check-notification-subscription-status)
+  - [Delete notification subscription](#delete-notification-subscription)
+  - [Error responses](#error-responses)
+- [Threat model](#threat-model)
+
+## Introduction
+
+SimpleX Messaging servers already operate as push servers and deliver the messages to subscribed clients as soon as they are sent to the servers.
+
+The reason for push notifications is to support instant message notifications on iOS that does not allow background services.
+
+## Participating servers
+
+The diagram below shows which servers participate in message notification delivery.
+
+While push provider (e.g., APN) can learn how many notifications are delivered to the user, it cannot access message content, even encrypted, or any message metadata - the notifications are e2e encrypted between SimpleX Notification Server and the user's device.
+
+```
+  User's iOS device                Internet                           Servers
+---------------------   .   ------------------------   .   -----------------------------
+                        .                              .
+                        .                              .       can be self-hosted now
++--------------+        .                              .         +----------------+
+| SimpleX Chat |       -------------- TLS ---------------        | SimpleX        |
+|    client    |------> SimpleX Messaging Protocol (SMP) ------> | Messaging      |
++--------------+       ----------------------------------        | Server         |
+     ^    |             .                              .         +----------------+
+     |    |             .                              .          . . .  |   . . .
+     |    |             .                              .               | V |
+     |    |             .                              .               |SMP| TLS
+     |    |             .                              .               | | |               SimpleX
+     |    |             .                              .          . . .  V   . . .      NTF Server
+     |    |             .                              .       +----------------------------------+
+     |    |             .                              .       | +---------------+                |
+     |    |            -------------- TLS ---------------      | | SimpleX       | can be         | 
+     |    |----------->   Notification Server Protocol  -----> | | Notifications | self-hosted    |
+     |                 ----------------------------------      | | Subscriber    | in the future  |
+     |                  .                              .       | +---------------+                |
+     |                  .                              .       |         |                        |
+     |                  .                              .       |         V                        |
+     |                  .                              .       | +---------------+                |
+     |                  .                              .       | | SimpleX       |                |
+     |                  .                              .       | | Push          |                |
+     |                  .                              .       | | Server        |                |
+     |                  .                              .       | +---------------+                |
+     |                  .                              .       +----------------------------------+
+     |                  .                              .          . . .  |   . . .
+     |                  .                              .               | V |
+     |                  .                              .               |SMP| TLS
+     |                  .                              .               | | |
+     |                  .                              .          . . .  V   . . .
+     |                 -------------- TLS ---------------       +-----------------+
+     |-----------------       Notification delivery     <-------| Apple PN server |
+                       ----------------------------------       +-----------------+
+                        .                              .
+```
+
+## Register device token to receive push notifications
+
+This diagram shows the process of registering a device to receive PUSH notifications via Apple Push Notification (APN) servers.
+
+![Register device notification token](./diagrams/notifications/register-token.svg)
+
+## Subscribe to connection notifications
+
+This diagram shows the process of subscription to notifications, notification delivery and device token update.
+
+![Subscribe to notifications](./diagrams/notifications/subscription.svg)
+
+## SimpleX Notification Server protocol
+
+To manage notification subscriptions to SMP servers, SimpleX Notification Server provides an RPC protocol with a similar design to SimpleX Messaging Protocol server.
+
+This protocol sends requests and responses in a fixed size blocks of 512 bytes over TLS, uses the same [syntax of protocol transmissions](./simplex-messaging.md#smp-transmission-and-transport-block-structure) as SMP protocol, and has the same transport [handshake syntax](./simplex-messaging.md#transport-handshake) (except the server certificate is not included in the handshake).
+
+Protocol commands have this syntax:
+
+```
+ntfServerTransmission = 
+ntfServerCmd = newTokenCmd / verifyTokenCmd / checkTokenCmd /
+               replaceTokenCmd / deleteTokenCmd / cronCmd /
+               newSubCmd / checkSubCmd / deleteSubCmd
+```
+### Register new notification token
+
+This command should be used after the client app obtains a token from push notifications provider to register the token with the server.
+
+Having received this command the server will deliver a test notification via the push provider to validate that the client has this token.
+
+The command syntax:
+
+```abnf
+newTokenCmd = %s"TNEW" SP newToken
+newToken = %s"T" deviceToken authPubKey clientDhPubKey
+deviceToken = pushProvider tokenString
+pushProvider = apnsDev / apnsProd / apnsNull
+apnsDev = "AD" ; APNS token for development environment
+apnsProd = "AP" ; APNS token for production environment
+apnsNull = "AN" ; token that does not trigger any notification delivery - used for server testing
+tokenString = shortString
+authPubKey = length x509encoded ; Ed25519 key used to verify clients commands
+clientDhPubKey = length x509encoded ; X25519 key to agree e2e encryption between the server and client
+shortString = length *OCTET
+length = 1*1 OCTET
+```
+
+The server response syntax:
+
+```abnf
+tokenIdResp = %s"IDTKN" SP entityId serverDhPubKey
+entityId = shortString
+serverDhPubKey = length x509encoded ; X25519 key to agree e2e encryption between the server and client
+```
+
+### Verify notification token
+
+This command is used to verify the token after the device receives the test notification from the push provider.
+
+The command syntax:
+
+```abnf
+verifyTokenCmd = %s"TVFY" SP regCode
+regCode = shortString
+```
+
+The response to this command is `okResp` or `errorResp`
+
+```abnf
+okResp = %s"OK"
+```
+
+### Check notification token status
+
+This command is used to check the token status:
+
+```abnf
+checkTokenCmd = %s"TCHK"
+```
+
+The response to this command:
+
+```abnf
+tokenStatusResp = %s"TKN" SP tokenStatus
+tokenStatus = %s"NEW" / %s"REGISTERED" / %s"INVALID" / %s"CONFIRMED" / %s"ACTIVE" / %s"EXPIRED"
+```
+
+### Replace notification token
+
+This command should be used when push provider issues a new notification token.
+
+It happens when:
+- the app data is migrated to another device.
+- the app is re-installed on the same device.
+- can happen periodically, at push provider discretion.
+
+This command allows to replace the token without re-registering and re-subscribing all notification subscriptions.
+
+Using this command triggers the same verification flow as registering a new token.
+
+The command syntax:
+
+```abnf
+replaceTokenCmd = %s"TRPL" SP deviceToken
+```
+
+The response to this command is `okResp` or `errorResp`.
+
+### Delete notification token
+
+The command syntax:
+
+```abnf
+deleteTokenCmd = %s"TDEL"
+```
+
+The response to this command is `okResp` or `errorResp`.
+
+After this command all message notification subscriptions will be removed and no more notifications will be sent.
+
+### Subscribe to periodic notifications
+
+This command enables or disables periodic notifications sent to the client device irrespective of message notifications.
+
+This is useful for two reasons:
+- it provides better privacy from notification server, as while the server learns the device token, it doesn't learn anything else about user communications.
+- it allows to receive messages when notifications were dropped by push provider, e.g. while the device was offline, or lost by notification server, e.g. while it was restarting.
+
+The command syntax:
+
+```abnf
+cronCmd = %s"TCRN" SP interval
+interval = 2*2 OCTET ; Word16, minutes
+```
+
+The interval for periodic notifications is set in minutes, with the minimum of 20 minutes. The client should pass `0` to disable periodic notifications.
+
+### Create SMP message notification subscription
+
+This command makes notification server subscribe to message notifications from SMP server and to deliver them to push provider:
+
+```abnf
+newSubCmd = %s"SNEW" newSub
+newSub = %s "S" tokenId smpServer notifierId notifierKey
+tokenId = shortString ; returned in response to `TNEW` command
+smpServer = smpServer = hosts port fingerprint
+hosts = length 1*host
+host = shortString
+port = shortString
+fingerprint = shortString
+notifierId = shortString ; returned by SMP server in response to `NKEY` SMP command
+notifierKey = length x509encoded ; private key used to authorize requests to subscribe to message notifications
+```
+
+The response syntax:
+
+```abnf
+subIdResp = %s"IDSUB" SP entityId
+```
+
+### Check notification subscription status
+
+This command syntax:
+
+```abnf
+checkSubCmd = %s"SCHK"
+```
+
+The response:
+
+```abnf
+subStatusResp = %s"SUB" SP subStatus
+subStatus = %s"NEW" / %s"PENDING" / ; e.g., after SMP server disconnect/timeout while ntf server is retrying to connect
+            %s"ACTIVE" / %s"INACTIVE" / %s"END" / ; if another server subscribed to notifications
+            %s"AUTH" / subErrStatus
+subErrStatus = %s"ERR" SP shortString
+```
+
+### Delete notification subscription
+
+The command syntax:
+
+```abnf
+deleteSubCmd = %s"SDEL"
+```
+
+The response to this command is `okResp` or `errorResp`.
+
+After this command no more message notifications will be sent from this queue.
+
+### Error responses
+
+All commands can return error response:
+
+```abnf
+errorResp = %s"ERR" SP errorType
+```
+
+Where `errorType` has the same syntax as in [SimpleX Messaging Protocol](./simplex-messaging.md#error-responses)
+
+## Threat Model
+
+This threat model compliments SimpleX Messaging Protocol [threat model](./overview-tjr.md#threat-model)
+
+#### A passive adversary able to monitor the traffic of one user
+
+*can:*
+
+ - identify that and a user is using SimpleX push notifications.
+
+*cannot:*
+
+ - determine which servers a user subscribed to the notifications from.
+
+#### A passive adversary able to monitor a set of senders and recipients
+
+ *can:*
+
+ - perform more efficient traffic correlation attacks against senders and recipients and correlate senders and recipients within the monitored set, frustrated by the number of users on the servers.
+
+#### SimpleX Messaging Protocol server
+
+*can:*
+
+- learn which messages trigger push notifications.
+
+- learn IP address of SimpleX notification servers used by the user.
+
+- drop message notifications.
+
+- spam a user with invalid notifications.
+
+*cannot:*
+
+- learn user device token for push notifications.
+
+- learn which queues belong to the same users with any additional efficiency compared with not using push notifications.
+
+#### SimpleX Notification Server subscribed to message notifications
+
+*can:*
+
+- learn a user device token.
+
+- learn how many messaging queues and servers a user receives messages from.
+
+- learn how many message notifications are delivered to the user from each queue.
+
+- undetectably drop notifications.
+
+- spam a user with background notifications.
+
+*cannot:*
+
+- learn queue addresses for receiving or sending messages.
+
+- learn the contents or type of messages (not even encrypted).
+
+- learn anything about messages sent without notification flag.
+
+- spam a user with visible notifications (provided the client app can filter push notifications).
+
+- add, duplicate, or corrupt individual messages that will be shown to the user.
+
+#### SimpleX Notification Server subscribed ONLY to periodic notifications
+
+*can:*
+
+- learn a user device token.
+
+- drop periodic notifications.
+
+- spam a user with background notifications.
+
+*cannot:*
+
+- learn how many messaging queues and servers a user receives messages from.
+
+- learn how many message notifications are delivered to the user from each queue.
+
+- learn queue addresses for receiving or sending messages.
+
+- learn the contents or type of messages (not even encrypted).
+
+- learn anything about messages sent without notification flag.
+
+- spam a user with visible notifications (provided the client app can filter push notifications).
+
+- add, duplicate, or corrupt individual messages that will be shown to the user.
+
+#### A user’s contact
+
+*cannot:*
+
+- determine if a user uses push notifications or not.
+
+#### Push notification provider (e.g., APN)
+
+*can:*
+
+- learn that a user uses SimpleX app.
+
+- learn how many notifications are delivered to user's device.
+
+- drop notifications (in fact, APN coalesces notifications delivered while user's device is offline, delivering only the last one).
+
+*cannot:*
+
+- learn which SimpleX Messaging Protocol servers are used by a user (notifications are e2e encrypted).
+
+- learn which or how many messaging queues a user receives notifications from.
+
+- learn the contents or type of messages (not even encrypted, notifications only contain encrypted metadata).
+
+#### An attacker with Internet access
+
+*cannot:*
+
+- register notification token not present on attacker's device.
+
+- enumerate tokens or subscriptions on a SimpleX Notification Server.

protocol/xftp-uri-request.txt

@@ -0,0 +1,16 @@
+Scheme name: xftp
+
+Status: Provisional
+
+Applications/protocols that use this scheme name:
+This scheme is used for URIs of XFTP (SimpleX File Transfer Protocol) servers,
+a client-server protocol for asynchronous file transfer via relays,
+preserving file meta-data (including size and name) and content privacy.
+
+Contact: Evgeny Poberezkin <ep@simplex.chat>
+
+Change controller: Evgeny Poberezkin <ep@simplex.chat>
+
+References:
+The syntax for server URIs in the provisional specification for SimpleX File Transfer Protocol:
+https://github.com/simplex-chat/simplexmq/blob/master/rfcs/2022-12-26-simplex-file-transfer.md#server-address-syntax

protocol/xftp.md

@@ -0,0 +1,632 @@
+Version 2, 2024-06-22
+
+# SimpleX File Transfer Protocol
+
+## Table of contents
+
+- [Abstract](#abstract)
+- [Introduction](#introduction)
+- [XFTP Model](#xftp-model)
+- [Persistence model](#persistence-model)
+- [XFTP procedure](#xftp-procedure)
+- [File description](#file-description)
+- [URIs syntax](#uris-syntax)
+  - [XFTP server URI](#xftp-server-uri)
+  - [File description URI](#file-description-URI)
+- [XFTP qualities and features](#xftp-qualities-and-features)
+- [Cryptographic algorithms](#cryptographic-algorithms)
+- [File chunk IDs](#file-chunk-ids)
+- [Server security requirements](#server-security-requirements)
+- [Transport protocol](#transport-protocol)
+  - [TLS ALPN](#tls-alpn)
+  - [Connection handshake](#connection-handshake)
+  - [Requests and responses](#requests-and-responses)
+- [XFTP commands](#xftp-commands)
+  - [Correlating responses with commands](#correlating-responses-with-commands)
+  - [Command authentication](#command-authentication)
+  - [Keep-alive command](#keep-alive-command)
+  - [File sender commands](#file-sender-commands)
+    - [Register new file chunk](#register-new-file-chunk)
+    - [Add file chunk recipients](#add-file-chunk-recipients)
+    - [Upload file chunk](#upload-file-chunk)
+    - [Delete file chunk](#delete-file-chunk)
+  - [File recipient commands](#file-recipient-commands)
+    - [Download file chunk](#download-file-chunk)
+    - [Acknowledge file chunk download](#acknowledge-file-chunk-download)
+- [Threat model](#threat-model)
+
+## Abstract
+
+SimpleX File Transfer Protocol is a client-server protocol for asynchronous unidirectional file transmission.
+
+It's designed with the focus on communication security, integrity and meta-data privacy, under the assumption that any part of the message transmission network can be compromised.
+
+It is designed as a application level protocol to solve the problem of secure and private file transmission, making [MITM attacks][1] very difficult at any part of the file transmission system, and preserving meta-data privacy of the sent files.
+
+## Introduction
+
+The objective of SimpleX File Transfer Protocol (XFTP) is to facilitate the secure and private unidirectional transfer of files from senders to recipients via persistent file chunks stored by the xftp server.
+
+XFTP is implemented as an application level protocol on top of HTTP2 and TLS.
+
+The protocol describes the set of commands that senders and recipients can send to XFTP servers to create, upload, download and delete file chunks of several pre-defined sizes. XFTP servers SHOULD support chunks of 4 sizes: 64KB, 256KB, 1MB and 4MB (1KB = 1024 bytes, 1MB = 1024KB).
+
+The protocol is designed with the focus on meta-data privacy and security. While using TLS, the protocol does not rely on TLS security by using additional encryption to achieve that there are no identifiers or ciphertext in common in received and sent server traffic, frustrating traffic correlation even if TLS is compromised.
+
+XFTP does not use any form of participants' identities. It relies on out-of-band passing of "file description" - a human-readable YAML document with the list of file chunk locations, hashes and necessary cryptographic keys.
+
+## XFTP Model
+
+The XFTP model has three communication participants: the recipient, the file server (XFTP server) that is chosen and, possibly, controlled by the sender, and the sender.
+
+XFTP server allows uploading fixed size file chunks, with or without basic authentication. The same party that can be the sender of one file chunk can be the recipient of another, without exposing it to the server.
+
+Each file chunk allows multiple recipients, each recipient can download the same chunk multiple times. It allows depending on the threat model use the same recipient credentials for multiple parties, thus reducing server ability to understand the number of intended recipients (but server can still track IP addresses to determine it), or use one unique set of credentials for each recipient, frustrating traffic correlation on the assumption of compromised TLS. In the latter case, senders can create a larger number of recipient credentials to hide the actual number of intended recipients from the servers (which is what SimpleX clients do).
+
+```
+           Sender                      Internet                XFTP relays             Internet         Recipient
+----------------------------   |   -----------------   |   -------------------   |   ------------   |   ---------- 
+                               |                       |                         |                  |
+                               |                       |   (can be self-hosted)  |                  |
+                               |                       |        +---------+      |                  |
+                  chunk 1     ----- HTTP2 over TLS ------       |  XFTP   |     ---- HTTP2 / TLS -----   chunk 1
+                |---> SimpleX File Transfer Protocol (XFTP) --> |  Relay  | --->        XFTP         ------------->|
+                |             ---------------------------       +---------+     ----------------------             |
+                |              |                       |                         |                  |              | 
+                |              |                       |                         |                  |              v
+          +----------+         |                       |        +---------+      |                  |        +-------------+
+          | Sending  | ch. 2  ------- HTTP2 / TLS -------       |  XFTP   |     ---- HTTP2 / TLS ----  ch. 2 |  Receiving  |
+file ---> |   XFTP   | ------>           XFTP            ---->  |  Relay  | --->        XFTP         ------> |     XFTP    | ---> file
+          |  Client  |        ---------------------------       +---------+     ----------------------       |    Client   |
+          +----------+         |                       |                         |                  |        +-------------+
+                |              |                       |                         |                  |              ^
+                |              |                       |        +---------+      |                  |              |
+                |             ------- HTTP2 / TLS -------       |  XFTP   |     ---- HTTP2 / TLS ----              |
+                |------------->           XFTP           ---->  |  Relay  | --->        XFTP         ------------->|
+                   chunk N    ---------------------------       +---------+     ---------------------    chunk N
+                               |                       |   (store file chunks)   |                  |
+                               |                       |                         |                  |
+                               |                       |                         |                  |
+```
+
+When sender client uploads a file chunk, it has to register it first with one sender ID and multiple recipient IDs, and one random unique key per ID to authenticate sender and recipients, and also provide its size and hash that will be validated when chunk is uploaded.
+
+To send the actual file, the sender client MUST pad it and encrypt it with a random symmetric key and distribute chunks of fixed sized across multiple XFTP servers. Information about chunk locations, keys, hashes and required keys is passed to the recipients as "[file description](#file-description)" out-of-band.
+
+Creating, uploading, downloading and deleting file chunks requires sending commands to the XFTP server - they are described in detail in [XFTP commands](#xftp-commands) section.
+
+## Persistence model
+
+Server stores file chunk records in memory, with optional adding to append-only log, to allow restoring them on server restart. File chunk bodies can be stored as files or as objects in any object store (e.g. S3).
+
+## XFTP procedure
+
+1. Sending the file.
+
+To send the file, the sender will:
+
+1) Prepare file
+  - compute its SHA512 digest.
+  - prepend header with the name and pad the file to match the whole number of chunks in size. It is RECOMMENDED to use 2 of 4 allowed chunk sizes, to balance upload size and metadata privacy.
+  - encrypt it with a randomly chosen symmetric key and IV (e.g., using NaCL secret_box).
+  - split into allowed size chunks.
+  - generate per-recipient keys. It is recommended that the sending client generates more per-recipient keys than the actual number of recipients, rounding up to a power of 2, to conceal the actual number of intended recipients.
+
+2) Upload file chunks
+  - register each chunk record with randomly chosen one or more (for redundancy) XFTP server(s).
+  - optionally request additional recipient IDs, if required number of recipient keys didn't fit into register request.
+  - upload each chunk to chosen server(s).
+
+3) Prepare file descriptions, one per recipient.
+
+The sending client combines addresses of all chunks and other information into "file description", different for each file recipient, that will include:
+
+- an encryption key used to encrypt/decrypt the full file (the same for all recipients).
+- file SHA512 digest to validate download.
+- list of chunk descriptions; information for each chunk:
+  - private Ed25519 key to sign commands for file transfer server.
+  - chunk address (server host and chunk ID).
+  - chunk sha512 digest.
+
+To reduce the size of file description, chunks are grouped by the server host.
+
+4) Send file description(s) to the recipient(s) out-of-band, via pre-existing secure and authenticated channel. E.g., SimpleX clients send it as messages via SMP protocol, but it can be done via any other channel.
+
+![Sending file](./diagrams/xftp/xftp-sending-file.svg)
+
+2. Receiving the file.
+
+Having received the description, the recipient will:
+
+1) Download all chunks.
+
+The receiving client can fall back to secondary servers, if necessary:
+- if the server is not available.
+- if the chunk is not present on the server (ERR AUTH response).
+- if the hash of the downloaded file chunk does not match the description.
+
+Optionally recipient can acknowledge file chunk reception to delete file ID from server for this recipient.
+
+2) Combine the chunks into a file.
+
+3) Decrypt the file using the key in file description.
+
+4) Extract file name and unpad the file.
+
+5) Validate file digest with the file description.
+
+![Receiving file](./diagrams/xftp/xftp-receiving-file.svg)
+
+## File description
+
+"File description" is a human-readable YAML document that is sent via secure and authenticated channel.
+
+It includes these fields:
+- `party` - "sender" or "recipient". Sender's file description is required to delete the file.
+- `size` - padded file size equal to total size of all chunks, see `fileSize` syntax below.
+- `digest` - SHA512 hash of encrypted file, base64url encoded string.
+- `key` - symmetric encryption key to decrypt the file, base64url encoded string.
+- `nonce` - nonce to decrypt the file, base64url encoded string.
+- `chunkSize` - default chunk size, see `fileSize` syntax below.
+- `replicas` - the array of file chunk replicas descriptions.
+- `redirect` - optional property for redirect information indicating that the file is itself a description to another file, allowing to use file description as a short URI.
+
+Each replica description is an object with 2 fields:
+
+- `chunks` - and array of chunk replica descriptions stored on one server.
+- `server` - [server address](#xftp-server-uri) where the chunks can be downloaded from.
+
+Each server replica description is a string with this syntax:
+
+```abnf
+chunkReplica = chunkNo ":" replicaId ":" replicaKey [":" chunkDigest [":" chunkSize]]
+chunkNo = 1*DIGIT
+  ; a sequential 1-based chunk number in the original file.
+replicaId = base64url
+  ; server-assigned random chunk replica ID.
+replicaKey = base64url
+  ; sender-generated random key to receive (or to delete, in case of sender's file description) the chunk replica.
+chunkDigest = base64url
+  ; chunk digest that MUST be specified for the first replica of each chunk,
+  ; and SHOULD be omitted (or be the same) on the subsequent replicas
+chunkSize = fileSize
+fileSize = sizeInBytes / sizeInUnits
+  ; chunk size SHOULD only be specified on the first replica and only if it is different from default chunk size
+sizeInBytes = 1*DIGIT
+sizeInUnits = 1*DIGIT sizeUnit
+sizeUnit = %s"kb" / %s"mb" / %s"gb"
+base64url = <base64url encoded binary> ; RFC4648, section 5
+```
+
+Optional redirect information has two fields:
+- `size` - the size of the original encrypted file to which file description downloaded via the current file description will lead to, see `fileSize` syntax below.
+- `digest` - SHA512 hash of the original file, base64url encoded string.
+
+## URIs syntax
+
+### XFTP server URI
+
+The XFTP server address is a URI with the following syntax:
+
+```abnf
+xftpServerURI = %s"xftp://" xftpServer
+xftpServer = serverIdentity [":" basicAuth] "@" srvHost [":" port]
+srvHost = <hostname> ; RFC1123, RFC5891
+port = 1*DIGIT
+serverIdentity = base64url
+basicAuth = base64url
+```
+
+### File description URI
+
+This file description URI can be generated by the client application to share a small file description as a QR code or as a link. Practically, to be able to scan a QR code it should be under 1000 characters, so only file descriptions with 1-2 chunks can be used in this case. This is supported with `redirect` property when file description leads to a file which in itself is a larger file description to another file - akin to URL shortener.
+
+File description URI syntax:
+
+```abnf
+fileDescriptionURI = serviceScheme "/file"  "#/?desc=" description [ "&data=" userData ]
+serviceScheme = (%s"https://" clientAppServer) | %s"simplex:"
+clientAppServer = hostname [ ":" port ]
+; client app server, e.g. simplex.chat
+description = <URI-escaped YAML file description>
+userData = <any URI-compatible string>
+```
+
+clientAppServer is not a server the client connects to - it is a server that shows the instruction on how to download the client app that will connect using this connection request. This server can also host a mobile or desktop app manifest so that this link is opened directly in the app if it is installed on the device.
+
+"simplex" URI scheme in serviceScheme can be used instead of client app server. Client apps MUST support this URI scheme.
+
+## XFTP qualities and features
+
+XFTP stands for SimpleX File Transfer Protocol. Its design is based on the same ideas and has some of the qualities of SimpleX Messaging Protocol:
+
+- recipient cannot see sender's IP address, as the file fragments (chunks) are temporarily stored on multiple XFTP relays.
+- file can be sent asynchronously, without requiring the sender to be online for file to be received.
+- there is no network of peers that can observe this transfer - sender chooses which XFTP relays to use, and can self-host their own.
+- XFTP relays do not have any file metadata - they only see individual chunks, with access to each chunk authorized with anonymous credentials (using Edwards curve cryptographic signature) that are random per chunk.
+- chunks have one of the sizes allowed by the servers - 64KB, 256KB, 1MB and 4MB chunks, so sending a large file looks indistinguishable from sending many small files to XFTP server. If the same transport connection is reused, server would only know that chunks are sent by the same user.
+- each chunk can be downloaded by multiple recipients, but each recipient uses their own key and chunk ID to authorize access, and the chunk is encrypted by a different key agreed via ephemeral DH keys (NaCl crypto_box (SalsaX20Poly1305 authenticated encryption scheme ) with shared secret derived from Curve25519 key exchange) on the way from the server to each recipient. XFTP protocol as a result has the same quality as SMP protocol - there are no identifiers and ciphertext in common between sent and received traffic inside TLS connection, so even if TLS is compromised, it complicates traffic correlation attacks.
+- XFTP protocol supports redundancy - each file chunk can be sent via multiple relays, and the recipient can choose the one that is available. Current implementation of XFTP protocol in SimpleX Chat does not support redundancy though.
+- the file as a whole is encrypted with a random symmetric key using NaCl secret_box.
+
+## Cryptographic algorithms
+
+Clients must cryptographically authorize XFTP commands, see [Command authentication](#command-authentication).
+
+To authorize/verify transmissions clients and servers MUST use either signature algorithm Ed25519 algorithm defined in RFC8709 or using deniable authentication scheme based on NaCL crypto_box (see Simplex Messaging Protocol).
+
+To encrypt/decrypt file chunk bodies delivered to the recipients, servers/clients MUST use NaCL crypto_box.
+
+Clients MUST encrypt file chunk bodies sent via XFTP servers using use NaCL crypto_box.
+
+## File chunk IDs
+
+XFTP servers MUST generate a separate new set of IDs for each new chunk - for the sender (that uploads the chunk) and for each intended recipient. It is REQUIRED that:
+
+- These IDs are different and unique within the server.
+- Based on random bytes generated with cryptographically strong pseudo-random number generator.
+
+## Server security requirements
+
+XFTP server implementations MUST NOT create, store or send to any other servers:
+
+- Logs of the client commands and transport connections in the production environment.
+
+- History of retrieved files.
+
+- Snapshots of the database they use to store file chunks (instead clients can manage redundancy by creating chunk replicas using more than one XFTP server). In-memory persistence is recommended for file chunks records.
+
+- Any other information that may compromise privacy or [forward secrecy][4] of communication between clients using XFTP servers.
+
+## Transport protocol
+
+- binary-encoded commands sent as fixed-size padded block in the body of HTTP2 POST request, similar to SMP and notifications server protocol transmission encodings.
+- HTTP2 POST with a fixed size padded block body for file upload and download.
+
+Block size - 4096 bytes (it would fit ~120 Ed25519 recipient keys).
+
+The reasons to use HTTP2:
+
+- avoid the need to have two hostnames (or two different ports) for commands and file uploads.
+- compatibility with the existing HTTP2 client libraries.
+
+The reason not to use JSON bodies:
+
+- bigger request size, so fewer recipient keys would fit in a single request
+- signature over command has to be outside of JSON anyway.
+
+The reason not to use URI segments / HTTP verbs / REST semantics is to have consistent request size.
+
+### ALPN to agree handshake version
+
+Client and server use [ALPN extension][18] of TLS to agree handshake version.
+
+Server SHOULD send `xftp/1` protocol name and the client should confirm this name in order to use the current protocol version. This is added to allow support of older clients without breaking backward compatibility and to extend or modify handshake syntax.
+
+If the client does not confirm this protocol name, the server would fall back to v1 of XFTP protocol.
+
+### Transport handshake
+
+When a client and a server agree on handshake version using ALPN extension, they should proceed with XFTP handshake.
+
+As with SMP, a client doesn't reveal its version range to avoid version fingerprinting. Unlike SMP, XFTP runs a HTTP2 protocol over TLS and the server can't just send its handshake right away. So a session handshake is driven by client-sent requests:
+
+1. To pass initiative to the server, the client sends a request with empty body.
+2. Server responds with its `paddedServerHello` block.
+3. Clients sends a request containing `paddedClientHello` block,
+4. Server sends an empty response, finalizing the handshake.
+
+Once TLS handshake is complete, client and server will exchange blocks of fixed size (16384 bytes).
+
+```abnf
+paddedServerHello = <padded(serverHello, 16384)>
+serverHello = xftpVersionRange sessionIdentifier serverCert signedServerKey ignoredPart
+xftpVersionRange = minXftpVersion maxXftpVersion
+minXftpVersion = xftpVersion
+maxXftpVersion = xftpVersion
+sessionIdentifier = shortString
+; unique session identifier derived from transport connection handshake
+serverCert = originalLength <x509encoded>
+signedServerKey = originalLength <x509encoded> ; signed by server certificate
+
+paddedClientHello = <padded(clientHello, 16384)>
+clientHello = xftpVersion keyHash ignoredPart
+; chosen XFTP protocol version - must be the maximum supported version
+; within the range offered by the server
+
+xftpVersion = 2*2OCTET ; Word16 version number
+keyHash = shortString
+shortString = length length*OCTET
+length = 1*1OCTET
+originalLength = 2*2OCTET
+ignoredPart = *OCTET
+```
+
+In XFTP v2 the handshake is only used for version negotiation, but `serverCert` and `signedServerKey` must be validated by the client.
+
+`keyHash` is the CA fingerprint used by client to validate TLS certificate chain and is checked by a server against its own key.
+
+`ignoredPart` in handshake allows to add additional parameters in handshake without changing protocol version - the client and servers must ignore any extra bytes within the original block length.
+
+For TLS transport client should assert that `sessionIdentifier` is equal to `tls-unique` channel binding defined in [RFC 5929][14] (TLS Finished message struct); we pass it in `serverHello` block to allow communication over some other transport protocol (possibly, with another channel binding).
+
+### Requests and responses
+
+- File sender:
+  - create file chunk record.
+    - Parameters:
+      - Ed25519 key for subsequent sender commands and Ed25519 keys for commands of each recipient.
+      - chunk size.
+    - Response:
+      - chunk ID for the sender and different IDs for all recipients.
+  - add recipients to file chunk
+    - Parameters:
+      - sender's chunk ID
+      - Ed25519 keys for commands of each recipient.
+    - Response:
+      - chunk IDs for new recipients.
+  - upload file chunk.
+  - delete file chunk (invalidates all recipient IDs).
+- File recipient:
+  - download file chunk:
+    - chunk ID
+    - DH key for additional encryption of the chunk.
+    - command should be signed with the key passed by the sender when creating chunk record.
+  - delete file chunk ID (only for one recipient): signed with the same key.
+
+## XFTP commands
+
+Commands syntax below is provided using ABNF with case-sensitive strings extension.
+
+```abnf
+xftpCommand = ping / senderCommand / recipientCmd / serverMsg
+senderCommand = register / add / put / delete
+recipientCmd = get / ack
+serverMsg = pong / sndIds / rcvIds / ok / file
+```
+
+The syntax of specific commands and responses is defined below.
+
+### Correlating responses with commands
+
+Commands are made via HTTP2 requests, responses to commands are correlated as HTTP2 responses.
+
+### Command authentication
+
+XFTP servers must authenticate all transmissions (excluding `ping`) by verifying the client signatures. Command signature should be generated by applying the algorithm specified for the file to the `signed` block of the transmission, using the key associated with the file chunk ID (recipient's or sender's depending on which file chunk ID is used).
+
+### Keep-alive command
+
+To keep the transport connection alive and to generate noise traffic the clients should use `ping` command to which the server responds with `pong` response. This command should be sent unsigned and without file chunk ID.
+
+```abnf
+ping = %s"PING"
+```
+
+This command is always sent unsigned.
+
+  data FileResponse = ... | FRPong | ...
+
+```abnf
+pong = %s"PONG"
+```
+
+### File sender commands
+
+Sending any of the commands in this section (other than `register`, that is sent without file chunk ID) is only allowed with sender's ID.
+
+#### Register new file chunk
+
+This command is sent by the sender to the XFTP server to register a new file chunk.
+
+Servers SHOULD support basic auth with this command, to allow only server owners and trusted users to create file chunks on the servers.
+
+The syntax is:
+
+```abnf
+register = %s"FNEW " fileInfo rcvPublicAuthKeys basicAuth
+fileInfo = sndKey size digest
+sndKey = length x509encoded
+size = 1*DIGIT
+digest = length *OCTET
+rcvPublicAuthKeys = length 1*rcvPublicAuthKey
+rcvPublicAuthKey = length x509encoded
+basicAuth = "0" / "1" length *OCTET
+
+x509encoded = <binary X509 key encoding>
+
+length = 1*1 OCTET
+```
+
+If the file chunk is registered successfully, the server must send `sndIds` response with the sender's and recipients' file chunk IDs:
+
+```abnf
+sndIds = %s"SIDS " senderId recipientIds
+senderId = length *OCTET
+recipientIds = length 1*recipientId
+recipientId = length *OCTET
+```
+
+#### Add file chunk recipients
+
+This command is sent by the sender to the XFTP server to add additional recipient keys to the file chunk record, in case number of keys requested by client didn't fit into `register` command. The syntax is:
+
+```abnf
+add = %s"FADD " rcvPublicAuthKeys
+rcvPublicAuthKeys = length 1*rcvPublicAuthKey
+rcvPublicAuthKey = length x509encoded
+```
+
+If additional keys were added successfully, the server must send `rcvIds` response with the added recipients' file chunk IDs:
+
+```abnf
+rcvIds = %s"RIDS " recipientIds
+recipientIds = length 1*recipientId
+recipientId = length *OCTET
+```
+
+#### Upload file chunk
+
+This command is sent by the sender to the XFTP server to upload file chunk body to server. The syntax is:
+
+```abnf
+put = %s"FPUT"
+```
+
+Chunk body is streamed via HTTP2 request.
+
+If file chunk body was successfully received, the server must send `ok` response.
+
+```abnf
+ok = %s"OK"
+```
+
+#### Delete file chunk
+
+This command is sent by the sender to the XFTP server to delete file chunk from the server. The syntax is:
+
+```abnf
+delete = %s"FDEL"
+```
+
+Server should delete file chunk record, invalidating all recipient IDs, and delete file body from file storage. If file chunk was successfully deleted, the server must send `ok` response.
+
+### File recipient commands
+
+Sending any of the commands in this section is only allowed with recipient's ID.
+
+#### Download file chunk
+
+This command is sent by the recipient to the XFTP server to download file chunk body from the server. The syntax is:
+
+```abnf
+get = %s"FGET " rDhKey
+rDhKey = length x509encoded
+```
+
+If requested file is successfully located, the server must send `file` response. File chunk body is sent as HTTP2 response body.
+
+```abnf
+file = %s"FILE " sDhKey cbNonce
+sDhKey = length x509encoded
+cbNonce = <nonce used in NaCl crypto_box encryption scheme>
+```
+
+Chunk is additionally encrypted on the way from the server to the recipient using a key agreed via ephemeral DH keys `rDhKey` and `sDhKey`, so there is no ciphertext in common between sent and received traffic inside TLS connection, in order to complicate traffic correlation attacks, if TLS is compromised.
+
+#### Acknowledge file chunk download
+
+This command is sent by the recipient to the XFTP server to acknowledge file reception, deleting file ID from server for this recipient. The syntax is:
+
+```abnf
+ack = %s"FACK"
+```
+
+If file recipient ID is successfully deleted, the server must send `ok` response.
+
+In current implementation of XFTP protocol in SimpleX Chat clients don't use FACK command. Files are automatically expired on servers after configured time interval.
+
+## Threat model
+
+#### Global Assumptions
+
+ - A user protects their local database and key material.
+ - The user's application is authentic, and no local malware is running.
+ - The cryptographic primitives in use are not broken.
+ - A user's choice of servers is not directly tied to their identity or otherwise represents distinguishing information about the user.
+
+#### A passive adversary able to monitor the traffic of one user
+
+*can:*
+
+ - identify that and when a user is sending files over XFTP protocol.
+
+ - determine which servers the user sends/receives files to/from.
+
+ - observe how much traffic is being sent, and make guesses as to its purpose.
+
+*cannot:*
+
+ - see who sends files to the user and who the user sends the files to.
+
+#### A passive adversary able to monitor a set of file senders and recipients
+
+ *can:*
+
+ - learn which XFTP servers are used to send and receive files for which users.
+
+ - learn when files are sent and received.
+
+ - perform traffic correlation attacks against senders and recipients and correlate senders and recipients within the monitored set, frustrated by the number of users on the servers.
+
+ - observe how much traffic is being sent, and make guesses as to its purpose
+
+*cannot, even in case of a compromised transport protocol:*
+
+ - perform traffic correlation attacks with any increase in efficiency over a non-compromised transport protocol
+
+#### XFTP server
+
+*can:*
+
+- learn when file senders and recipients are online.
+
+- know how many file chunks and chunk sizes are sent via the server.
+
+- perform the correlation of the file chunks as belonging to one file via either a re-used transport connection, user's IP address, or connection timing regularities.
+
+- learn file senders' and recipients' IP addresses, and infer information (e.g. employer) based on the IP addresses, as long as Tor is not used.
+
+- delete file chunks, preventing file delivery, as long as redundant delivery is not used.
+
+- lie about the state of a file chunk to the recipient and/or to the sender  (e.g. deleted when it is not).
+
+- refuse deleting the file when instructed by the sender.
+
+*cannot:*
+
+- undetectably corrupt file chunks.
+
+- learn the contents, name or the exact size of sent files.
+
+- learn approximate size of sent files, as long as more than one server is used to send file chunks.
+
+- compromise the users' end-to-end encryption of files with an active attack.
+
+#### An attacker who obtained Alice's (decrypted) chat database
+
+*can:*
+
+- see the history of all files exchanged by Alice with her communication partners, as long as files were not deleted from the database.
+
+- receive all files sent and received by Alice that did not expire yet, as long as information about these files was not removed from the database.
+
+- prevent Alice's contacts from receiving the files she sent by deleting all or some of the file chunks from XFTP servers.
+
+#### A user's contact
+
+*can:*
+
+- spam the user with files.
+
+- forever retain files from the user.
+
+*cannot:*
+
+- cryptographically prove to a third-party that a file came from a user (assuming the user's device is not seized).
+
+- prove that two contacts they have is the same user.
+
+- cannot collaborate with another of the user's contacts to confirm they are communicating with the same user, even if they receive the same file.
+
+#### An attacker with Internet access
+
+*can:*
+
+- Denial of Service XFTP servers.
+
+*cannot:*
+
+- send files to a user who they are not connected with.
+
+- enumerate file chunks on an XFTP server.

protocol/xrcp-uri-request.txt

@@ -0,0 +1,15 @@
+Scheme name: xrcp
+
+Status: Provisional
+
+Applications/protocols that use this scheme name:
+This scheme is used for URIs of controller sessions via SimpleX Remote Control protocol (XRCP),
+a protocol for remote access and management of hosts via insecure network.
+
+Contact: Evgeny Poberezkin <ep@simplex.chat>
+
+Change controller: Evgeny Poberezkin <ep@simplex.chat>
+
+References:
+The syntax for server URIs in the provisional specification for SimpleX File Transfer Protocol:
+https://github.com/simplex-chat/simplexmq/blob/master/rfcs/2023-10-25-remote-control.md#session-invitation

protocol/xrcp.md

@@ -0,0 +1,330 @@
+Version 1, 2024-06-22
+
+# SimpleX Remote Control Protocol
+
+## Table of contents
+
+- [Abstract](#abstract)
+- [XRCP model](#xrcp-model)
+- [Transport protocol](#transport-protocol)
+  - [Session invitation](#session-invitation)
+  - [Establishing TLS connection](#establishing-tls-connection)
+  - [Session verification and protocol negotiation](#session-verification-and-protocol-negotiation)
+  - [Controller/host session operation](#сontrollerhost-session-operation)
+- [Key agreement for announcement packet and for session](#key-agreement-for-announcement-packet-and-for-session)
+- [Threat model](#threat-model)
+
+## Abstract
+
+The SimpleX Remote Control Protocol is a client-server protocol designed to transform application UIs into thin clients, enabling remote control from another device. This approach allows users to remotely access and utilize chat profiles without the complexities of master-master replication for end-to-end encryption states.
+
+Like SMP and XFTP, XRCP leverages out-of-band invitations to mitigate MITM attacks and employs multiple cryptographic layers to safeguard application data.
+
+## XRCP model
+
+XRCP assumes two application roles: host (that contain the application data) and controller that gains limited access to host data.
+Applications are also split into two components: UI and core.
+
+When an XRCP session is established a host UI is locked out and a controller UI uses its core to proxy commands to the host core, getting back responses and events.
+
+```
+
+          +------+              +------+     xrcp     +------+     +------+
+          | Ctrl |   commands   | Ctrl |   commands   | Host |     | Host |
+user ---> |  UI  | -----------> | Core | -----------> | Core |     |  UI  |
+          +------+              +------+              +------+     +------+
+              ^     responses     |  ^  xrcp responses  |  ^
+              |<------------------|  |<-----------------|  |      +-------------+
+              |      events       |                        |      | Application |-+
+              |<------------------|                        |----> |   protocol  | |
+                                                                  |   servers   | |
+                                                                  +-------------+ |
+                                                                   +--------------+
+```
+
+## Transport protocol
+
+Protocol consists of four phases:
+- controller session invitation
+- establishing session TLS connection
+- session verification and protocol negotiation
+- session operation
+
+![Session sequence](./diagrams/xrcp/session.svg)
+
+### Session invitation
+
+The invitation to the first session between host and controller pair MUST be shared out-of-band, to establish a long term identity keys/certificates of the controller to host device.
+
+The subsequent sessions can be announced via an application-defined site-local multicast group, e.g. `224.0.0.251` (also used in mDNS/bonjour) and an application-defined port (SimpleX Chat uses 5227).
+
+The session invitation contains this data:
+- supported version range for remote control protocol.
+- application-specific information, e.g. device name, application name and supported version range, settings, etc.
+- session start time in seconds since epoch.
+- if multicast is used, counter of announce packets sent by controller.
+- network address (ipv4 address and port) of the controller.
+- CA TLS certificate fingerprint of the controller - this is part of long term identity of the controller established during the first session, and repeated in the subsequent session announcements.
+- Session Ed25519 public key used to verify the announcement and commands - this mitigates the compromise of the long term signature key, as the controller will have to sign each command with this key first.
+- Long-term Ed25519 public key used to verify the announcement and commands - this is part of the long term controller identity.
+- Session X25519 DH key and SNTRUP761 KEM encapsulation key to agree session encryption (both for multicast announcement and for commands and responses in TLS), as described in https://datatracker.ietf.org/doc/draft-josefsson-ntruprime-hybrid/. The new keys are used for each session, and if client key is already available (from the previous session), the computed shared secret will be used to encrypt the announcement multicast packet. The out-of-band invitation is unencrypted. DH public key and KEM encapsulation key are sent unencrypted. NaCL crypto_box is used for encryption.
+
+Host application decrypts (except the first session) and validates the invitation:
+- Session signature is valid.
+- Timestamp is within some window from the current time.
+- Long-term key signature is valid.
+- Long-term CA and signature key are the same as in the first session.
+- Some version in the offered range is supported.
+
+OOB session invitation is a URI with this syntax:
+
+```abnf
+sessionAddressUri = "xrcp:/" encodedCAFingerprint "@" host ":" port "#/?" qsParams
+encodedCAFingerprint = base64url
+host = <ipv4 or ipv6 address> ; in textual form, RFC4001
+port = 1*DIGIT ; uint16
+qsParams = param *("&" param)
+param = versionRangeParam / appInfoParam / sessionTsParam /
+        sessPubKeyParam / idPubKeyParam / dhPubKeyParam /
+        sessSignatureParam / idSignatureParam
+versionRangeParam = "v=" (versionParam / (versionParam "-" versionParam))
+versionParam = 1*DIGIT
+appInfoParam = "app=" escapedJSON
+sessionTsParam = "ts=" 1*DIGIT
+sessPubKeyParam = "skey=" base64url
+idPubKeyParam = "idkey=" base64url
+dhPubKeyParam = "dh=" base64url
+sessSignatureParam = "ssig=" base64url ; signs the URI with this and idSignatureParam param removed
+idSignatureParam = "idsig=" base64url ; signs the URI with this param removed
+base64url = <base64url encoded binary> ; RFC4648, section 5
+```
+
+Multicast session announcement is a binary encoded packet with this syntax:
+
+```abnf
+sessionAddressPacket = dhPubKey nonce encrypted(unpaddedSize sessionAddress packetPad)
+dhPubKey = length x509encoded ; same as announced
+nonce = length *OCTET
+sessionAddress = largeLength sessionAddressUri ; as above
+length = 1*1 OCTET ; for binary data up to 255 bytes
+largeLength = 2*2 OCTET ; for binary data up to 65535 bytes
+packetPad = <pad packet size to 1450 bytes> ; possibly, we may need to move KEM agreement one step later,
+; with encapsulation key in HELLO block and KEM ciphertext in reply to HELLO.
+```
+
+### Establishing TLS connection
+
+Both controller and host use 2-element certificate chains with unique self-signed CA root representing long-term identities. Leaf certificates aren't stored and instead generated on each session start.
+
+A controller runs a TCP server to avoid opening listening socket on a host, which might create an attack vector. A controller keeps no sensitive data to be exposed this way.
+
+During TLS handshake, parties validate certificate chains against previously known (from invitation or storage) CA fingerprints. The fingerprints MUST be the same as in the invitation and in the subsequent connections.
+
+### Session verification and protocol negotiation
+
+Once TLS session is established, both the host and controller devices present a "session security code" to the user who must match them (e.g., visually or via QR code scan) and confirm on the host device. The session security code must be a digest of tlsunique channel binding. As it is computed as a digest of the TLS handshake for both the controller and the host, it will validate that the same TLS certificates are used on both sides, and that the same TLS session is established, mitigating the possibility of MITM attack in the connection.
+
+Once the session is confirmed by the user, the host sends HELLO block to the controller.
+
+XRCP blocks inside TLS are padded to 16384 bytes.
+
+Host HELLO block must contain:
+- new session DH key - used to compute new shared secret with the controller keys from the announcement.
+- encrypted part of HELLO block (JSON object), containing:
+  - chosen protocol version.
+  - host CA TLS certificate fingerprint - part of host long term identity - must match the one presented in TLS handshake and the previous sessions, otherwise the connection is terminated.
+  - KEM encapsulation key - used to compute new shared secret for the session.
+  - additional application specific parameters, e.g host device name, application version, host settings or JSON encoding format.
+
+Host HELLO block syntax:
+
+```abnf
+hostHello = %s"HELLO " dhPubKey nonce encrypted(unpaddedSize hostHelloJSON helloPad) pad
+unpaddedSize = largeLength
+dhPubKey = length x509encoded
+pad = <pad block size to 16384 bytes>
+helloPad = <pad hello size to 12888 bytes>
+largeLength = 2*2 OCTET
+```
+
+The controller decrypts (including the first session) and validates the received HELLO block:
+- Chosen versions are supported (must be within offered ranges).
+- CA fingerprint matches the one presented in TLS handshake and the previous sessions - in subsequent sessions TLS connection should be rejected if the fingerprint is different.
+
+[JTD schema](https://www.rfc-editor.org/rfc/rfc8927) for the encrypted part of host HELLO block `hostHelloJSON`:
+
+```json
+{
+  "definitions": {
+    "version": {
+      "type": "string",
+      "metadata": {
+        "format": "[0-9]+"
+      }
+    },
+    "base64url": {
+      "type": "string",
+      "metadata": {
+        "format": "base64url"
+      }
+    }
+  },
+  "properties": {
+    "v": {"ref": "version"},
+    "ca": {"ref": "base64url"},
+    "kem": {"ref": "base64url"}
+  },
+  "optionalProperties": {
+    "app": {"properties": {}, "additionalProperties": true}
+  },
+  "additionalProperties": true
+}
+```
+
+The controller should reply with with `ctrlHello` or `ctrlError` response:
+
+```abnf
+ctrlHello = %s"HELLO " kemCiphertext nonce encrypted(unpaddedSize ctrlHelloJSON helloPad) pad
+; ctrlHelloJSON is encrypted with the hybrid secret,
+; including both previously agreed DH secret and KEM secret from kemCiphertext
+unpaddedSize = largeLength
+kemCiphertext = largeLength *OCTET
+pad = <pad block size to 16384 bytes>
+helloPad = <pad hello size to 12888 bytes>
+largeLength = 2*2 OCTET
+
+ctrlError = %s"ERROR " nonce encrypted(unpaddedSize ctrlErrorMessage helloPad) pad
+ctrlErrorMessage = <utf-8 encoded text>; encrypted using previously agreed DH secret.
+```
+
+JTD schema for the encrypted part of controller HELLO block `ctrlHelloJSON`:
+
+```json
+{
+  "properties": {},
+  "additionalProperties": true
+}
+```
+
+Once the controller replies HELLO to the valid host HELLO block, it should stop accepting new TCP connections.
+
+### Controller/host session operation
+
+The protocol for communication during the session is out of scope of this protocol.
+
+SimpleX Chat uses HTTP2 encoding, where host device acts as a server and controller acts as a client (these roles are reversed compared with TLS connection, restoring client-server semantics in HTTP).
+
+Payloads in the protocol must be encrypted using NaCL secret_box using the hybrid shared secret agreed during session establishment.
+
+Commands of the controller must be signed after the encryption using the controller's session and long term Ed25519 keys.
+
+tlsunique channel binding from TLS session MUST be included in commands (included in the signed body).
+
+The syntax for encrypted command and response body encoding:
+
+```abnf
+commandBody = encBody sessSignature idSignature [attachment]
+responseBody = encBody [attachment] ; counter must match command
+encBody = nonce encLength32 encrypted(tlsunique counter body)
+attachment = %x01 nonce encLength32 encrypted(attachment)
+noAttachment = %x00
+tlsunique = length 1*OCTET
+counter = 8*8 OCTET ; int64
+encLength32 = 4*4 OCTET ; uint32, includes authTag
+```
+
+If the command or response includes attachment, its hash must be included in command/response and validated.
+
+## Key agreement for announcement packet and for session
+
+Initial announcement is shared out-of-band (URI with xrcp scheme), and it is not encrypted.
+
+This announcement contains only DH keys, as KEM key is too large to include in QR code, which are used to agree encryption key for host HELLO block. The host HELLO block will contain DH key in plaintext part and KEM encapsulation (public) key in encrypted part, that will be used to determine the shared secret (using SHA256 over concatenated DH shared secret and KEM encapsulated secret) both for controller HELLO response (that contains KEM ciphertext in plaintext part) and subsequent session commands and responses.
+
+During the next session the announcement is sent via encrypted multicast block. The shared key for this announcement and for host HELLO block is determined using the KEM shared secret from the previous session and DH shared secret computed using the host DH key from the previous session and the new controller DH key from the announcement.
+
+For the session, the shared secret is computed again using the KEM shared secret encapsulated by the controller using the new KEM key from the host HELLO block and DH shared secret computed using the host DH key from HELLO block and the new controller DH key from the announcement.
+
+In pseudo-code:
+
+```
+// session 1
+hostHelloSecret(1) = dhSecret(1)
+sessionSecret(1) = sha256(dhSecret(1) || kemSecret(1)) // to encrypt session 1 data, incl. controller hello
+dhSecret(1) = dh(hostHelloDhKey(1), controllerInvitationDhKey(1))
+kemCiphertext(1) = enc(kemSecret(1), kemEncKey(1))
+// kemEncKey is included in host HELLO, kemCiphertext - in controller HELLO
+kemSecret(1) = dec(kemCiphertext(1), kemDecKey(1))
+
+// multicast announcement for session n
+announcementSecret(n) = sha256(dhSecret(n'))
+dhSecret(n') = dh(hostHelloDhKey(n - 1), controllerDhKey(n))
+
+// session n
+hostHelloSecret(n) = dhSecret(n)
+sessionSecret(n) = sha256(dhSecret(n) || kemSecret(n)) // to encrypt session n data, incl. controller hello
+dhSecret(n) = dh(hostHelloDhKey(n), controllerDhKey(n))
+// controllerDhKey(n) is either from invitation or from multicast announcement
+kemCiphertext(n) = enc(kemSecret(n), kemEncKey(n))
+kemSecret(n) = dec(kemCiphertext(n), kemDecKey(n))
+```
+
+If controller fails to store the new host DH key after receiving HELLO block, the encryption will become out of sync and the host won't be able to decrypt the next announcement. To mitigate it, the host should keep the last session DH key and also previous session DH key to try to decrypt the next announcement computing shared secret using both keys (first the new one, and in case it fails - the previous).
+
+To decrypt a multicast announcement, the host should try to decrypt it using the keys of all known (paired) remote controllers.
+
+## Threat model
+
+#### A passive network adversary able to monitor the site-local traffic:
+
+*can:*
+- observe session times, duration and volume of the transmitted data between host and controller.
+
+*cannot:*
+- observe the content of the transmitted data.
+- substitute the transmitted commands or responses.
+- replay transmitted commands or events from the hosts.
+
+#### An active network adversary able to intercept and substitute the site-local traffic:
+
+*can:*
+- prevent host and controller devices from establishing the session
+
+*cannot:*
+- same as passive adversary, provided that user visually verified session code out-of-band.
+
+#### An active adversary with the access to the network:
+
+*can:*
+- spam controller device.
+
+*cannot:*
+- compromise host or controller devices.
+
+#### An active adversary with the access to the network who also observed OOB announcement:
+
+*can:*
+- connect to controller instead of the host.
+- present incorrect data to the controller.
+
+*cannot:*
+- connect to the host or make host connect to itself.
+
+#### Compromised controller device:
+
+*can:*
+- observe the content of the transmitted data.
+- access any data of the controlled host application, within the capabilities of the provided API.
+
+*cannot:*
+- access other data on the host device.
+- compromise host device.
+
+#### Compromised host device:
+
+*can:*
+- present incorrect data to the controller.
+- incorrectly interpret controller commands.
+
+*cannot:*
+- access controller data, even related to this host device.

rfcs/2024-02-12-encryption.md

@@ -0,0 +1,33 @@
+# Transmission encryption
+
+## Problems
+
+### Protection of meta-data from sending proxy
+
+The SEND commands and message queue IDs need to be encrypted so that sending proxy cannot see how many queues exist on each server.
+
+Correlation IDs need to be random and can be re-used as nonces so that the destination relay cannot use the increasing correlation IDs that are sent in v6 of the protocol to track the sender.
+
+###  Protection of the traffic from the attacker who compromised TLS
+
+Currently, even though different sending and receiving queue IDs are used, the attacker who compromised TLS could do statistical analysis and in this way correlate queue IDs of senders and recipients, and therefore correlate the senders and recipients.
+
+## Possible solutions
+
+1. Encrypt sent messages, other commands and their responses in the additional envelope, irrespective of whether proxy is used or not. In this case the requestion transmission could have this syntax:
+
+```abnf
+encReqTransmission = pubKey nonce encrypted(reqTransmission)
+reqTransmission = respNonce entityId command
+
+encRespTransmission = replyNonce encrypted(respTransmission)
+respTransmission = entityId command
+```
+
+The keys to encrypt and decrypt both the command and responses would be computed as curve25519 from the key sent together with command and server session key. For the requests, the nonce has to be random and sent outside of the encrypted envelopt, but for the response respNonce would be taken from inside of the encrypted envelope and it would also be used for correlating commands and responses. This way the attacker who could compromise TLS would not be able to correlate the commands and responses, and also observe entity IDs.
+
+2. The remaining question is to how encrypt and decrypt messages delivered not in response to the commands.
+
+The possible options are:
+- restore client session key only for that purpose, but do not forward this key to the destination proxy for sent messages. Then the messages can be sent with a random replyNonce and the key would be computed from session keys. The advantage here is that we won't need to parameterize handles as both client and server would have session keys. The downside that we would have to either somehow differentiate messages and responses, either by some flag that would allow some correlation or just by the absense of replyNonce in the lookup map - that is if the client can find replyNonce, it would use the associated key to decrypt, and if not it would use session key.
+- use the same key that was sent with SUB or ACK command. This is much more complex, and would only have some upside if we were to introduce receiving proxies (to conceal transport sessions from the receiving relays for the recipients).

rfcs/2024-03-20-server-metadata.md

@@ -0,0 +1,130 @@
+# Relay metadata and SimpleX network decentralization
+
+## Problem
+
+Currently, the clients configure/choose which servers to use, but they cannot see who operates them, in which geography and hosting provider, what is the server source code (in case it was modified from the reference implementation we provide) and also any administrative and feedback contacts.
+
+Further, we currently use simplex.chat domain to host group links, and as diversity of the groups grows it is beginning to require managing feedback from the users about groups. It is important that this feedback is directed to relay owners and not to us, in case they are not our relays, as we are simply providing software here.
+
+We also need to make it much easier to access administrative actions - e.g., if the relay owner wants to block some address based on the feedback, they should be able to do so effectively. While freedom of speech of users is important the autonomy and sovereignty of relay operators allowing them to decide what they want or don't want to host, irrespective of the reasons, is as important - public relays constitute a public space rather than a service, and while there is no authentication or authorization required to use them, the relay owners should be able to decide their conditions and limitations of use, as is the case for any public space.
+
+## Why it is important
+
+1. We are building network and not a service, so contrary to the traditional approach when service collects users metadata and conceals its own, it appears important to do the opposite - expose all relay metadata that may have any effect on users privacy and security and provide access to this metadata with the minimal friction, via the app UI.
+2. We need to remove the only remaining bit of centralization - using simplex.chat website to show the QR code and help new users onboarding - this role can be delegated to the relays.
+3. We need to make it easy for the users to submit feedback and to the relay operators to manage that feedback. That includes ourselves, as relay operators, and also any other person or organization that operates public relays.
+4. It is important to stress the requirement of AGPLv3 license to provide access to the source code to the relay users, as any code modifications might undermine user privacy and security and must be made transparent to the relay users.
+
+While this document is not the end of the journey to decentralize the network, it's an important first step.
+
+## Proposed solution
+
+The proposed solution consists of two parts:
+
+- communicate server metadata via protocol, so it can be observed by the clients.
+- create home page for the relays, with all the same metadata.
+- create invitation and address links in the same domain name as the relay.
+
+The latter point is important so it is clear to the users who operates and owns the relay and where the access point to the content or group is hosted. Even though simplex.chat domain is never accessed by the app, and the meaningful part of the address is never sent to the page hosting server, it creates an impression of centralization, and some dependency on simplex.chat domain for anything other that showing the link QR code.
+
+Moving invitation links to the domain of the relay (primary relay, in case the link has redundancy) will both clarify relay ownership, solve the incorrect mis-perception of centralization, remove the dependency on simplex-chat domain without any user effort, and provides the means to submit content complaints to the relay operators (should they wish to receive them, which seems reasonable for large public relays, but may be unnecessary for private relays where unidentified parties cannot create links).
+
+## Solution details
+
+Extend server INI file with information section:
+
+```
+[INFORMATION]
+# Please note that under AGPLv3 license conditions you MUST make
+# any source code modifications available to the end users of the server.
+# LICENSE: https://github.com/simplex-chat/simplexmq/blob/stable/LICENSE
+# Not doing so would constitute a license violation.
+# Declaring an incorrect information here amounts to a fraud.
+# The license holders reserve the right to prosecute missing or incorrect
+# information about the server source code to the fullest extent permitted by the law.
+# The server will show warning on start if this field is absent
+# and will not launch from v6.0 until this field is added.
+# If any other information field is present, source code property also MUST be present.
+source_code: https://github.com/simplex-chat/simplexmq
+
+# Declaring all below information is optional, any of these fields can be omitted.
+# Declaring an incorrect information here would amount to a fraud.
+
+# We should split this document to the model one, where specific parameters will be external to the document,
+# and specific to us, so that relay operators can adopt our recommended policy and publish any amendments separately.
+usage_conditions: https://github.com/simplex-chat/simplex-chat/blob/_archived-ep/ios-file-provider/PRIVACY.md
+# condition_amendments: link
+
+server_country: SE
+operator: SimpleX Chat Ltd.
+operator_country: GB # operator country
+website: https://simplex.chat
+admin_simplex: administrative SimpleX address
+admin_email: chat@simplex.chat
+admin_pgp: PGP key
+complaints_simplex: SimpleX address for feedback, comments and complaints
+complaints_email: complaints@simplex.chat
+complaints_pgp: PGP key
+hosting: Linode / Akamai Inc.
+hosting_country: US
+```
+
+Server home page would show whether queue creation is allowed and/or password protected, server retention policy (e.g., preserve messages on restart or not, and persist connections or not).
+
+Server queue address/contact pages will optionally, provide the UI to submit feedback, comments and complaints directly from the web page (not an MVP, initially we would simply show addresses for feedback, and, probably, create link that opens in the app with pre-populated message, and we could also use this addresses defined in server meta-data to submit feedback from inside of the app - it's also out of MVP scope).
+
+If server is available on .onion address, the web pages would show "open via .onion" in Tor browser.
+
+Extend server handshake header with these information fields:
+
+```haskell
+data ServerHandshake = ServerHandshake
+  { smpVersionRange :: VersionRangeSMP,
+    sessionId :: SessionId,
+    -- pub key to agree shared secrets for command authorization and entity ID encryption.
+    authPubKey :: Maybe (X.CertificateChain, X.SignedExact X.PubKey),
+    -- ^^ existing fields
+    -- vv new field that will be sent as length-prefixed JSON in the handshake
+    information :: Maybe ServerInformation
+  }
+
+data ServerInformation = ServerInformation
+  { config :: ServerPublicConfig,
+    info :: ServerPublicInfo
+  }
+
+-- based on server configuration
+data ServerPublicConfig = ServerPublicConfig
+  { persistence :: SMPServerPersistenceMode,
+    messageExpiration :: Int,
+    statsEnabled :: Bool,
+    newQueuesAllowed :: Bool,
+    basicAuthEnabled :: Bool -- server is private if enabled
+  }
+
+-- based on INFORMATION section of INI file
+data ServerPublicInfo = ServerPublicInfo
+  { sourceCode :: Text, -- note that this property is not optional, in line with AGPLv3 license
+    conditions :: Maybe ServerConditions,
+    operator :: Maybe Entity,
+    website :: Maybe Text,
+    adminContacts :: Maybe ServerContactAddress,
+    complaintsContacts :: Maybe ServerContactAddress,
+    hosting :: Maybe Entity,
+    serverCountry :: Maybe Text
+  }
+
+data ServerPersistenceMode = SMPMemoryOnly | SPMQueues | SPMQueuesMessages
+
+data ServerConditions = ServerConditions {conditions :: Text, amendments :: Maybe Text}
+
+data Entity = Entity {name :: Text, country :: Maybe Text}
+
+data ServerContactAddress = ServerContactAddress
+  { simplex :: Maybe Text,
+    email :: Maybe Text, -- it is recommended that it matches DNS email address, if either is present
+    pgp :: Maybe Text
+  }
+```
+
+This extended server information will be stored in the chat database every time it changes and shown in the UI of the server configuration.

rfcs/2024-06-01-agent-protocol.md

@@ -0,0 +1,19 @@
+# Evolving agent API
+
+## Problem
+
+Historically, agent API started as a TCP protocol with encoding. We do not use the actual protocol and maintaining the encoding complicates the evolution of the API.
+
+Currently, I was trying to add ERRS event to combine multiple subscription errors into one to prevent overloading the UI with processing multiple subscription errors (e.g.):
+
+```haskell
+ERRS :: (ConnId, AgentErrorType) -> ACommand Agent AEConn
+```
+
+This constructor is not possible to encode/parse in a sensible way other than including lengths of errors.
+
+## Proposal
+
+Remove commands type and encodings for commands and events.
+
+Only keep encodings for the commands that are saved to the database: NEW, JOIN, LET, ACK, SWCH, DEL (this one is no longer used but needs to be supported for backwards compatibility).

rfcs/2024-07-06-ios-notifications.md

@@ -0,0 +1,18 @@
+# iOS notifications stability
+
+## Problem
+
+iOS notifications may fail to deliver for several reasons, but there are two important reasons that we could address:
+- when notification server is not subscribed to SMP server(s), the notifications can be dropped - it can happen because either notification server restarts or becuase SMP server restarted and some messages are received before notification server resubscribed. We lose approximately 3% of notifications because of this reason.
+- when user device is offline or has low power condition, Apple does not deliver notification, but puts them to storage. If while the notification is in storage a new one arrives it would overwrite the previous notification. If it was the message to the same message queue, the client will download messages anyway, up to a limit, but if the message was to another queue, it will not be delivered until the app is opened. Apple delivers about 88% of notifications that should be delivered (not accounting for uninstalled apps), the rest is replaced with the newer notifications.
+
+## Solution
+
+The first problem can be solved by preserving notifications for a limited time (say 1 hour) in case there is no subscription to notification from notification server. At the very least, they can be preserved in SMP server memory but can also be stored to a file on restart, similar to messages, and be delivered when notification server resubscribes. It is sufficient to store one notification per messaging queue.
+
+The second problem is both more damaging and more complex to solve. The solution could be to always deliver several last notifications to different queues in one packet (Apple allows up to ~4-5kb notification size, and we are sending packets of fixed size 512 bytes, so we could fit up to 8-10 of them in each notification).
+
+Every time a client receives such batch of notifications if can:
+- check if that notification was already received in the previous batch.
+- if it was received, it would be ignored, otherwise it would be processed.
+- process them one by one, started from the most recent one while the time allows.

rfcs/done/2022-11-11-smp-basic-auth.md

@@ -0,0 +1,27 @@
+# SMP Basic Auth
+
+## Problem
+
+Users who host their own servers do not want unknown people to be able to create messaging queues on their servers after discovering server address in groups or after making a connection. As the number of self-hosted servers is growing it became more important than it was when we excluded it from the original design.
+
+## Solution
+
+Single access password that can be optionally included in server address that is passed to app configuration. It will not be allowed in the existing contexts (and parsing will fail), to avoid accidentally leaking it. Server address with password will look this way: `smp://fingerprint:password@hosts`
+
+## Implementation plan
+
+1. A separate type to include server and password, so it can only be used where allowed.
+
+2. Server password to create queues will be configured in TRANSPORT section of INI file, as `create_password` parameter.
+
+3. The password will only be required in server configuration/address to create queues only, it won't be required for other receiving queue operations on already existing queues.
+
+4. If new command is attempted in the session that does not allow creating queues, the server will send `ERR AUTH` response
+
+5. Passing password to the server can be done in one of the several ways, we need to decide:
+
+  - as a parameter of NEW command. Pros: a local change, that only needs checking when queue is created. Cons: protocol version change.
+  - as a separate command AUTH. Pros: allows to include additional parameters and potentially be extended beyond basic auth. Cons: more complex to manage server state, can be more difficult syntax in the future, if extended.
+  - as part of handshake (we currently ignore the unparsed part of handshake block, so it can be extended). Pros: probably, the simplest, and independent of the commands protocol – establishes create permission for the current session. Cons: the client won't know about whether it is able to create the queue until it tries (same as in case 1).
+
+  My preference is the last option. As a variant of the last option, we can add a server response/message that includes permission to create queues - it will only be sent to the clients who pass credential in handshake - that might simplify testing server connection (we currently do not do it). It might be unnecessary, as we could simply create and delete queue in case credential is passed as part of testing connection (and even sending a message to it).

rfcs/done/2022-12-26-simplex-file-transfer.md

@@ -0,0 +1,173 @@
+# SimpleX File Transfer protocol
+
+## Problem
+
+Sending files as currently implemented in SimpleX Chat is inefficient for these reasons:
+
+1. Slow: message delivery requires acknowledgement for each message before the server sends the next message.
+2. Not fully asynchronous:
+   a. SMP queue size is limited, so the whole file cannot be sent/stored in server memory.
+   b. Recipient needs to accept the file before it is sent.
+3. No broadcast: sending the same file to multiple recipients requires sending it multiple times.
+
+## Possible solutions
+
+These problems could be solved within SMP protocol:
+
+- streaming messages without waiting for acknowledgements.
+- bigger queue sizes stored on hard drive and accepting large files without waiting for the recipient confirmation.
+- adding broadcast to SMP servers.
+
+These solution are complex and they do not scale well.
+
+Another approach would be adopting some open-source file storage, possibly S3-compatible, to host files while "in transit". The downsides are:
+
+1. Missing features. S3-compatible file servers require a service layer that we would need to develop to manage user accounts and permissions. There are solutions that allow self-registering users and uploading files without service layer, but they are not flexible enough in managing policies for these files.
+2. Limited meta-data protection, both on the application and on transport layer: same address for sending and receiving a file, file size is known to the server, etc.
+3. More difficult to self-host for the users when the server has 2 components (a 3rd party solution with our service component).
+
+We are not considering P2P solutions because of their bad meta-data privacy and requirement of having a single network - the same reason why P2P design is not used for SimpleX messaging network.
+
+A proposed solution is to develop a file hosting service (SimpleX File Transfer service) that would have better meta-data protection and functionality than the alternatives, using the ideas from SMP protocol design.
+
+The parameters of the solution would be:
+
+1. The server does not have knowledge of the users and actual files – only anonymously uploaded fixed-size chunks (considered 8Mb, maybe we should allow 2 sizes, e.g. 1Mb and 8Mb).
+2. The server should allow broadcast, so that a chunk can be downloaded by multiple recipients.
+3. There should be no identifiers and ciphertext in common inside TLS between sender and recipient traffic, and between the traffic of different recipients of the same file. This approach can be extended to support public chunks that have persistent identifiers.
+4. The server should prevent multiple uploads of the same chunk. This can be extended to allow multiple downloads from the same persistent address.
+5. Clients can send the chunks from the same file via multiple servers, both by splitting chunks between them and for redundancy.
+
+## Design approach
+
+File transfer servers will be chosen by file senders. The servers will allow senders to anonymously upload fixed-size file chunks.
+
+### Transport protocol
+
+- binary-encoded commands sent as fixed-size padded block in the body of HTTP2 POST request, similar to SMP and notifications server protocol transmission encodings.
+- HTTP2 POST with a fixed size padded block body for file upload and download.
+
+Block size - 4096 bytes (it would fit ~120 Ed25519 recipient keys).
+
+The reasons to use HTTP2:
+
+- avoid the need to have two hostnames (or two different ports) for commands and file uploads.
+- compatibility with the existing HTTP2 client libraries.
+
+The reason not to use JSON bodies:
+
+- bigger request size, so fewer recipient keys would fit in a single request
+- signature over command has to be outside of JSON anyway.
+
+The reason not to use URI segments / HTTP verbs / REST semantics is to have consistent request size.
+
+### Required server commands:
+
+- File sender:
+  - create file chunk record.
+    - Parameters:
+      - Ed25519 key for subsequent sender commands and Ed25519 keys for commands of each recipient.
+      - chunk size.
+    - Response:
+      - chunk ID for the sender and different IDs for all recipients.
+  - add recipients to file chunk
+    - Parameters:
+      - sender's chunk ID
+      - Ed25519 keys for commands of each recipient.
+    - Response:
+      - chunk IDs for new recipients.
+  - upload file chunk.
+  - delete file chunk (invalidates all recipient IDs).
+- File recipient:
+  - download file chunk:
+    - chunk ID
+    - DH key for additional encryption of the chunk.
+    - command should be signed with the key passed by the sender when creating chunk record.
+  - delete file chunk ID (only for one recipient): signed with the same key.
+
+### Storage model
+
+Same as for SMP and notifications server - in-memory storage of the records, with adding to append-only log, restored and compacted on server restart.
+
+### Sending file
+
+To send the file, the sender will:
+
+- compute SHA512 digest
+- pad the file to match the whole number of chunks in size,
+- encrypt it with a randomly chosen symmetric key and IV (e.g., using NaCL crypto_secretbox),
+- split into fixed size chunks
+- upload each chunk to a randomly chosen server.
+
+The sending client should generate more per-recipient keys than the actual number of recipients, possibly rounding up to a power of 2, to conceal the actual number of intended recipients.
+
+Then the sending client will combine addresses of all chunks and other information into "file description", different for each file recipient, that will include:
+
+- an encryption key that was used to encrypt the file (the same for all recipients).
+- file SHA512 digest
+- list of chunk descriptions; information for each chunk:
+  - private Ed25519 key to sign commands for file transfer server.
+  - chunk address (server host and chunk ID).
+  - chunk sha512 digest
+
+To reduce the size, chunk descriptions will be grouped by the server host.
+
+This "file description" itself will be sent as a small file over an authenticated channel, to prevent file description modification. To estimate its size:
+
+- each chunk \* redundancy per chunk, assuming chunks are grouped per server:
+  - 1-based chunk number in the file - 8 bytes (including any overhead)
+  - Ed25519 key (different for each recipient / chunk combination) - 32 bytes \* 4/3 (base64, assuming text encoding)
+  - chunk ID (different for each recipient) - 64 bytes \* 4/3
+  - optional (only in the first chunk occurence) chunk sha512 digests - 64 bytes \* 4/3
+- server addresses - say, 128 bytes per server
+- sha512 digest - 64 bytes \* 4/3
+- encryption key - 32 bytes \* 4/3
+- IV - 32 bytes \* 4/3
+- encoding overhead - say, 256 bytes
+
+For 1gb file, sent via 4 different servers, in 8Mb chunks, with redundancy 2, the size of "file description", assuming text encoding, will be ~45kb (`128 * (8 + 32 + 64) * 2 * 4/3 + 128 * 64 * 4/3 + 128 * 4 + (64 + 32 + 32) * 4/3 + 256`).
+
+File description format (yml):
+
+```
+name: file.ext
+size: 33200000
+chunk: 8mb
+hash: abc=
+key: abc=
+iv: abc=
+parts:
+  - server: xftp://abc=@example1.com
+    chunks: [1:abc=:def=:ghi=, 3:abc=:def=:ghi=]
+  - server: xftp://abc=@example2.com
+    chunks: [2:abc=:def=:ghi=, 4:abc=:def=:ghi=:2mb]
+  - server: xftp://abc=@example3.com
+    chunks: [1:abc=:def=, 4:abc=:def=]
+  - server: xftp://abc=@example4.com
+    chunks: [2:abc=:def=, 3:abc=:def=]
+```
+
+This file description is sent to all recipients via normal messages, split to 15780 byte chunks if needed.
+
+### Server address syntax
+
+The server address is a URI with the following format:
+
+```abnf
+xftpServerURI = %s"xftp://" xftpServer
+xftpServer = serverIdentity "@" srvHost [":" port]
+srvHost = <hostname> ; RFC1123, RFC5891
+port = 1*DIGIT
+serverIdentity = base64url
+base64url = <base64url encoded binary> ; RFC4648, section 5
+```
+
+### Receiving file
+
+Having received the description, the recipient will:
+
+- download all chunks falling back to secondary servers, if needed
+- combine the chunks into a file
+- decrypt the file
+- un-pad it
+- validate file digest

rfcs/done/2022-12-27-queue-quota.md

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+# SMP and SMP agent protocol extensions to manage queue quotas
+
+## Problem
+
+SMP servers define a limit on the number of messages that can be stored on the server. When the sender reaches this limit, they continue trying to send the message with exponential back off, until the server allows it. To reduce the traffic we added expiration on unsent messages of 2 days that:
+
+- adds its own set of problems because of expired control messages - e.g., group fragmentation.
+- doesn't solve problem of traffic in active groups with many inactive members - there are still too many retries in queues that reached capacity.
+
+## Solution
+
+Sending agent permanently stops trying to send messages having received `ERR QUOTA` (or, for the period of clients migration, increases TTL much more than in cases of network errors).
+
+Add SMP server event that means "quota reached" (e.g. `QTA` or `MSG QUOTA`) - it will be delivered to the recipient once all messages are retrieved at the same point in message stream where the sender received `ERR QUOTA`. Alternatively, it could be a message flag that is set on the last message in the queue at a point the sender received `ERR QUOTA`.
+
+Add SMP agent message that means "quota available, resume sending" (e.g. `A_QTA` or `A_RESUME`) – the receiving agent will send it via the reply queue to the sending agent that will resume sending messages at this point.
+
+Possibly, increase TTL for local messages to 30 days. That might require separately addressing the problem of permanently failing servers.
+
+We discussed a possible solution of merging all messages to one server into one delivery queue, so that having multiple failing queues on this server will not result in multiple connection attempts, and this proposal also answers the question what to do with the messages when quota is exceeded - the whole queue can be marked as suspended, and processed separately from others - TBD.

rfcs/done/2023-05-02-resync-ratchets.md

@@ -0,0 +1,58 @@
+# Re-sync encryption ratchets, queue rotation, message delivery receipts
+
+This is very unfocussed doc outlining several problems that seem somewhat related, and some possible solution approaches.
+
+## Problems
+
+When old database backup is used, the sending client encrypts the messages in a way that the receiving client cannot decrypt them, because it does not store the old keys, and does not try to decrypt ratchet headers using the old keys. When receiving the messages, the client that uses the old database is unable to decrypt them, either the header or the message itself (if more than 500 messages are skipped, or if root ratchet step happened).
+
+The same symptoms happen during the queue rotation, unfortunately, as we do not keep the history of received messages once they are acknowledged, so the client reports these error to the users.
+
+While these are two different problems, to the users they manifest in the same way, so it is difficult to differentiate.
+
+Another ratchet problem that should be solved as well is not deleting unused skipped keys after some time or some number of events, possibly it should be considered at the same time.
+
+While it is tempting to consider delivery receipts as an isolated problem, it is somewhat coupled, as the requests to re-sync ratchets and to re-deliver skipped messages are effectively delivery receipts.
+
+A naive solution to delivery receipts when each message is responded to with a confirmation has two downsides:
+
+- it doubles the traffic.
+- in the absense of delays, it also leaks some information about the network latency, that can be used to track user's location.
+
+Both problems can be mitigated by sending delivery receipts with a random delay, to confirm all messages sent, not each one. But this would only reduce the traffic when the sender sends many messages. Alternatively, we could think how to reduce the block size for SMP commands. The challenge is profile pictures and image previews, so to reduce traffic we need to start sending them as XFTP files, potentially with a smaller 64kb chunks (that would also increase preview quality).
+
+## Solution for queue rotation
+
+We need to:
+- store and show the rotation status in the UI to prevent attempts to rotate the queue multiple times.
+- process multiple message delivery events while there is a redundancy, to avoid errors in terminal.
+- differentiate between decryption errors during queue rotation - that would require keeping the messages for some time, at least keeping their IDs and hashes together with some additional status. In this case when duplicate or old message arrives, we can check whether this message was already processed, and do not show error if it was.
+
+## Solution to re-sync ratchets
+
+When we establish that the receiving client is indeed unable to decrypt messages, we should:
+- notify the user - it is already happening, but it happens in case of rotation as well.
+- optionally, notify another client that message was not decrypted - this effectively becomes a delivery receipt. That could be a separate command triggered by the user in the UI.
+- clients can get into this state at the same time, how do we handle concurrent requests? Possibly, we could design these messages so this is irrelevant whether the message is sent in response or not, and calculate the new ratchet keys once the clients have both the sent and received messages. After that both clients can send "ratchet reset" message:
+  - EKEY - message containing a new set of keys to initialize the ratchets
+  - EREADY - message confirming that the ratchet is ready, already e2e encrypted
+
+The downside of this approach, is that unlike the initial handshake, where the second ratchet key is sent in e2e encrypted response, this message will be sent only encrypted with queue key. We could change this protocol by adding EREPLY message, and the clients would know to ingnore EKEY with bigger hash of the keys, so that the client who sent keys with smaller hash would be processing response from another client (that is if EKEY is received after EKEY is sent).
+
+```
+A                B
+
+EKEY 1 ->        <- EKEY 2 (e2e encrypted with per-queue key only)
+EKEY 2 <-        -> EKEY 1
+1 < 2, wait      2 > 1, reply EREPLY 3 (e2e encrypted with ratchets)
+ratchet: 1, 3   ratchet: 3, 1
+```
+
+Once ratchets are re-synched the clients could additionally request delivery of skipped messages. As ratchets being out of sync is not the only problem when messages can be lost, it may be managed independently from the ratchet re-sync. This problem seems tied with delivery receipts too, as requesting to re-deliver some messages automatically confirms that some other messages were delivered.
+
+Alternatively, the request for ratchet sync can already contain the ID of the first failed message - that would allow the agent:
+- stop sending messages until ratchets are in sync.
+- re-deliver failed messages first.
+- only then deliver any pending messages.
+
+This approach would probably result in a better UX (no out of order delivery), but requires tracking pending messages that are not attempted to deliver and to also insert old messages in the delivery queue with the old IDs.

rfcs/done/2023-05-03-delivery-receipts.md

@@ -0,0 +1,170 @@
+# Delivery receipts
+
+## Problems
+
+User experience - users need to know that the messages are delivered to the recipient, as this confirms that the system is functioning.
+
+The downside of communicating message delivery as it confirms that the recipient was online, and, unless there is a delay in confirming, can be used to track the location via the variation in network latency. So delivery receipts should be delayed with a randomized interval and should be opt in or opt out.
+
+Another problem of message receipts is that they increase network traffic and server load. This could be avoided if delivery receipts are communicated as part of normal message delivery flow.
+
+Some other existing and planned features implicitely confirm message delivery and, possibly, should depend on message delivery being enabled:
+- agent message to resume delivery when quota was exceeded (implemented, [rfc](./2022-12-27-queue-quota.md))
+- agent message to re-deliver skipped messages or to re-negotiate double ratchet.
+
+## Solution
+
+There are three layers where delivery receipts can be implemented:
+- chat protocol. Pro: logic of when to deliver it is decoupled from the message flow, Con: extra traffic, can only work in duplex connections.
+- agent client protocol. Pro: can be automated and combined with the protocol to re-deliver skipped messages. Con: extra traffic.
+- SMP protocol. Pro: minimal extra traffic, Con: complicates server design as it would require pushing receipts when there is no next message.
+
+The last approach seems the most promising for avoiding additional traffic:
+- modify client ACK command to include whether delivery receipt should be provided to sender, and, possibly, any e2e encrypted data that should be included in the receipt (e.g., that the receiving client already saw this message in case we use "feedback" variant of roumor-mongering protocol for groups).
+- server would manage delaying of the receipts, by randomizing the time after which the receipt will be available to the sender, and by combining the receipts when possible.
+- modify response to SEND command to include any available delivery receipts.
+- add a separate delivery receipt that will be pushed to the sender in the connection where the message was received by the server.
+
+## SMP protocol changes
+
+```haskell
+data Command (p :: Party) where
+  -- ...
+  ACK :: MsgId -> Maybe ByteString -> Command Recipient
+  -- the presense of ByteString in ACK indicates that the delivery needs to be confirmed.
+  -- the protocol does not define the format of this confirmation, it is application specific, and can be -- an empty string.
+  -- And open question is how to e2e encrypt information in this string - this probably can be handled on Agent client protocol level, and could be the same ratchet key that was used to encrypt and decrypt the message. The downside of this approach is that this key currently is not stored, and storing it requires additional logic to clear these keys if unused after some time.
+  -- TODO consider what could be a better approach.
+  SENT :: MsgId -> [(MsgId, UTCTime, ByteString)] -> Command Sender
+  -- or
+  -- SENT :: MsgId -> Command Sender
+  -- in case we just batch
+  -- this response will be sent to SEND command and will include a sender's message ID generated by the server (currently it does not exist), and posibly an empty list of delivery receipts with the same message IDs as in responses to SEND, timestamps when these receipts became available, and e2e encrypted ByteString passed in ACK command.
+  -- The ID in this response should be different from the ID used in MSG, to keep the promise of not having shared identifiers in sent/received traffic even inside TLS tunnel.
+  -- Keeping the quality of shared ciphertext also requires adding additional encryption layer between the server and the sender, this can be achieved in one of two ways:
+  -- 1) passing a separate DH key in each SEND command, and server including additional DH key in each SENT response, with computed DH secret per message later used to encrypt and decrypt the delivery receipt payloads. This is probably a bad idea as it would increase a cryptographic load on both the server and the client.
+  -- 2) agree a key per queue, in the same way it is done for the recipient. Possibly, it requires additional DH key in confirmation message that the recipient then uses to secure the queue, and passing this key in KEY (secure queue) command. The response to this secure command would the include server's DH key returned to the recipient that would be passed to the sender in HELLO message. Even though recipient could observe both public DH keys, they won't know the computed shared secret. Recipient that controls the server could perform MITM attack on this key exchange, but it doesn't give any benefit over what recipient can do when they have access to the server - the threat model remains the same. The downside of this approach is that it also requires additional changes in client protocol level (confirmation message format and HELLO message).
+  -- 3) also agree on a key per queue, but via separate commands between the sender and the server, once the sender was notified that the queue is secured. This approach is probably better, and the server would simply delay the delivery of delivery receipts until the shared secret is agreed.
+  SKEY :: C.PublicKeyX25519 -> Command Sender
+  SBKEY :: C.PublicKeyX25519 -> BrokerMsg
+  -- these are the command and response to agree secret to encrypt delivery receipt payloads for option 3
+  SSUB :: Command Sender
+  -- subscribe to receive delivery receipts for a given queue - will be sent when the conversation is opened (unless there is an active subscription already), not all queues at once, and won't be re-subscribed on losing the server connection (TBC).
+  RCVD :: MsgId -> UTCTime -> ByteString -> Command Recipient
+  -- delivery receipt. UTCTime is the time when it became available, not the time when ACK was sent by the recipient, to avoid leaking location via network latency.
+```
+
+Possibly, there is no need to include delivery receipts into SENT response and instead just use batching of responses that is already supported. As server responses are not signed, there is no per-response overhead that is substantial, and a lot of receipts that are available can be packed into one block (depending on the size of payload that has to be fixed not to leak metadata).
+
+This all seems rather complicated for SMP protocol, and the approach of doing it on a higher level seems more attractive than initially. Possibly we should reconsider, and reduce traffic by reducing block sizes... Reducing block sizes unfortunately requires supporting variable block sizes, and would leak some metadata during the transition period.
+
+## Another approach
+
+Above represents substantial complexity, and at least doubles server code complexity for the feature that is definitely not doubling the value of server software. Moving to variable block size is simpler, but also has a lot of complexity, reduces metadata privacy (at least for the duration of migration period), reduces image preview quality, and requires postponing this feature for multiple releases, until all clients migrate.
+
+Given that the main traffic is generated by the groups, and direct messages do not create a lot of traffic, a much simpler and better solution is to simply send delivery receipts as the message, in direct conversations only, either as chat protocol message or as agent client protocol message (either on the message or on the envelope layer).
+
+### Comparison of these two approaches:
+
+**Chat protocol message**
+
+Pros:
+- simpler, more contained change - SMP layer is not aware of this feature
+- easier to extend protocol with additional application specific payload, e.g. references to group DAG
+Cons:
+- ?
+
+```json
+  // ...
+  "x.msg.delivered": {
+    "properties": {
+      "msgId": {"ref": "base64url"},
+      "params": {
+        "properties": {
+          "msgId": {"ref": "base64url"},
+        },
+        "optionalProperties": {
+          "data": {} // possibly the initial protocol does not need it, with JSON can be added later
+        }
+      }
+    }
+  },
+  // ...
+```
+
+**Agent client protocol envelope**
+
+Pros:
+- possibility of using it in a wider range of the applications
+- possibility to include received message hash to increase communication integrity - the sending client would be then notified, and it can be exposed in the UI, that the received message is not the same as sent.
+
+Cons:
+- additional implementation complexity - requires additional events to communicate between chat and agent.
+
+```haskell
+data AMessage =
+  -- ...
+  | A_RCVD AgentMsgId MsgHash ByteString -- references to the received message
+  -- ...
+```
+
+The weirdness of the above design is that it refers to the data present in the header of another message, the alternative would be to have a separate envelope for delivery receipt:
+
+```haskell
+data AgentMessage =
+  -- ...
+  AgentMessageRcvd APrivHeader AgentMsgId MsgHash ByteString -- references to the received message
+  -- ...
+```
+
+But probably the first one is a bit better, TBC.
+
+In any case there should be an additional event to notify chat client:
+
+```haskell
+data ACommand (p :: AParty) (e :: AEntity) where
+  -- ...
+  RCVD AgentMsgId MsgMeta ByteString -> ACommand Agent AEConn
+  -- ...
+```
+
+On the balance of things, implementing on the level of Agent Client protocol seems better, as the additional complexity is marginal, but it allows for wider range of applications, and also allows for additional delivery integrity validation. The format for payload still requires chat protocol message encoding once we want to add it, but initially it could be just an empty string.
+
+## Implementation plan
+
+Currently, we delete sent messages once delivered to the server. It would be helpful if we could keep the records in snd_messages table, and then use them to process delivery receipts, although it may be insufficient (we could add fields). Probably it is not possible to keep them as there is a foreign key constraint with `on delete cascade`.
+
+The new table will be used to track sent message hashes to correlate their IDs with delivery receipts (that will also be stored in messages/rcv_messages). Receipts need to be processed in chat in the same way as normal messages, so they would be sent to chat with MsgMeta, and the chat will need to ack them once processed.
+
+Agent ackMessage function will be also used to automatically schedule sending delivery receipts if they are enabled for connection, only for normal messages - no sending receipts to receipts.
+
+There can be receipt re-delivery to the chat in the same cases as when normal message can be re-delivered (in case of AGENT A_DUPLICATE when it was not ack'd by the user).
+
+## Other considerations
+
+### How clients decide whether to send delivery receipts
+
+Two options are possible - local settings per conversation or chat preferences framework, that allows to have mutual on/off. The latter seems preferable as without knowing whether the other party is sending receipts, it is not possible to uderstand what the absense of the receipt means - network malfunction or receipts disabled.
+
+Groups are a special case, as while some groups may enable sending the delivery receipts, the group members should be able to disable it locally. This should probably be done via a separate conversation setting in the same way as enabling notifications or favourites. In this case the receipt would only be sent to the group if it is enabled in the group and not disabled by the member. The toggle may be located in the same page as chat preferences, but it should be a separate setting. We might want though to communicate somehow whether a given member sends delivery receipts so that other members know whether to expect them or not.
+
+### How this functionality is released
+
+5.2:
+- support for sending and receiving delivery receipts preference, both in direct messages and in groups (for forward compatibility).
+- support for sending and receiving delivery receipts in direct chats only, but disable sending them
+
+5.3:
+- show receipt preferences in the UI
+- enable sending receipts in direct chats where they are enabled
+
+A separate question is how to enable this functionality for the existing contacts. Possible options are:
+
+1. Enable (as per default) for all contacts, show notification to the user when they open the app for update that delivery notifications are now sent by default to all contacts. Pro: no extra logic to implement. Con: may be perceived as a privacy violation, as to some contacts the delivery receipts will be sent before the user had chance to disable them.
+2. Ask the user when the new version first runs whether they want to use delivery receipts and offer these options:
+  1) keep enabled for all profiles (and for all contacts)
+  2) enable for all profiles in ~12 or in ~24 hours giving users the chance to review all contacts / profiles and disable some of them. The problem here is also in possibility of the correlation in case they all start sending receipts at the same time. Possibly the option could be to set a random time in 12-15 or 24-30 hours range to avoid the possibility of such correlation.
+  3) disable for all profiles – it will require sending profile updates to all contacts, so the delivery receipts should be kept disabled and profile updates should be sent after random intervals, one by one (not scheduled all at once, as the time may pass while the app is off).
+3. Offer an option to enable globally later - we could keep it as a one-off option, available only to existing users, and visible on the top level of the Settings - once enabled, the option will disappear and it won't be possible to disable again. The downside here is that the new contacts would be receiving the profile with enabled notifications but they still won't be delivered...
+4. Another option is to have all new contacts decided based on a global user default (that can be set in the settings and in the dialog on first start), but for the existing contacts keep in unset state that is not interpreted as either on or off, but interpreted as unknown until the user makes a choice... That might be an optimal solution for the users but it would probably require changing the preferences framework or some ad-hoc hacks. That still keeps the question open how to avoid correlation between profiles.
+5. That might be the case for version agreement too - the availability of the option per contact will depend on the version. It doesn't answer the question what to do with global defaults though...