docs: update connection diagram to include user-server authentication and encryption

diagrams/connection.mmd

@@ -1,24 +1,58 @@
 sequenceDiagram
   participant Alice
-  participant App A
-  participant Server A
-  participant Server B
-  participant App B
+  participant App A as Alice's app
+  participant Server A as Alice's server
+  participant Server B as Bob's server
+  participant App B as Bob's app
   participant Bob
-  Alice ->> App A: Alice shows <AB public key> as QR code on the screen<br>(Alice's public key for Bob's eyes only)
-  Bob ->> App B: Bob requests app to add connection
-  App A ->> App B: Bob's app reads <AB public key> via the camera
-  App B ->> Server B: Bob's app encrypts "connection request" (including <BA public key> and Bob's profile) and sends it to Bob's servers<br>{from: <BA public key hash>, to: <AB public key hash>, message: <request encrypted with AB public key>}
-  Server B ->> Server A: Bob's servers use <AB public key hash> to locate Alice's servers<br>and forward encrypted message to all Alice's servers (when they are different from Bob's servers)
-  Server A ->> App A: Alice's servers send the message to Alice's app
-  App A ->> Alice: Alice's app matches <AB public key hash> with shown QR code<br>and decrypts Bob's profile with <AB private key> to show it
+
+  Alice ->> App A: Alice requests app to initiate adding connection
+  Note over App A: App generates:<br><AB connection key><br><A_AB server keys>
+  App A ->> Server A: App registers on Alice's servers <AB public key hash> associated with <A_AB server public keys> (for recepient)
+  App A ->> Server A: App subsribes to receive messages from anyone sent to <AB public key hash><br>(request is signed with <A_AB server private keys>)
+
+  Note over App A: App shows QR code<br>for <AB public key><br>and Alice's servers
+
+  App A -->> Bob: Alice shows to Bob <AB public key> and her servers as QR code on the screen<br>(Alice's public key for Bob only and servers she currently uses)
+  Bob ->> App B: Bob requests app to read connection QR code
+  App A -->> App B: Bob's app reads QR code with <AB public key> and Alice's current servers via the camera
+
+  Note over App B: App generates<br><BA connection key><br><B_BA server keys>
+
+  App B ->> Server B: App registers on Bob's server <BA public key hash> associated with <B_BA server public keys> (for recepient)
+  App B ->> Server B: App subsribes to receive messages from anyone sent to <BA public key hash><br>(request is signed with <B_BA server private key>)
+
+  Note over App A, App B: Now both Alice's and Bob's apps are subscribed to receive each other's messages on their servers
+
+  Note over App B: App generates<br><B_AB server keys><br>for Alice's servers<br>and creates<br>connection request<br>including:<br>- <BA public key><br>- Bob's profile<br>- Bob's servers<br>- <B_AB public keys>
+  App B ->> Server A: Bob's app encrypts "connection request" with <AB public key> and sends it to Alice's servers<br>{to: <AB public key hash>, message: <request encrypted with AB public key>}
+  Server A ->> App A: Alice's servers send "connection request" to Alice's app<br>(as <AB public key hash> allows messages from anyone)
+  App A ->> Alice: Alice's app matches <AB public key hash> with <AB public key><br>and decrypts Bob's profile with <AB private key> to show it
   Alice ->> App A: Alice identifies Bob's profile and accepts the connection<br>(Bob is now added to Alice's list of connections as "pending")
-  App A ->> Server A: Alice's app creates "connection accepted" message (including Alice's profile) and sends it to Alice's servers<br>{from: <AB public key hash>, to: <BA public key hash>, message: <encrypted with AB public key>}
-  Server A ->> Server B: Alice's servers use <BA public key hash> to locate Bob's servers<br>and forward encrypted message to all Bob's servers (when they are different from Alice's servers)
+  App A ->> Server A: App registers on Alice's servers <AB public key hash> associated with <B_AB server public keys> (for sender)
+
+  Note over Server A, Bob: Now only Bob's app can send messages for <AB public key hash> to Alice's servers<br>1) signed using <BA private key><br>2) encrypted using <AB public key><br>3) signed/encrypted using <B_AB server private/public keys>
+
+  Note over App A: App generates<br><A_BA server keys><br>for Bob's servers<br>and creates<br>"conn. accepted"<br>message including:<br>- Alice's profile<br>- <A_BA public keys>
+
+  App A ->> Server B: Alice's app signs "connection accepted" with <AB private key>, encrypts it with <BA public key> and sends it to Bob's servers<br>{to: <BA public key hash>, message: <encrypted with BA public key>}
   Server B ->> App B: Bob's servers send the message to Bob's app
-  App B ->> Bob: Bob's app matches <AB public key hash> with read QR code<br>and decrypts the Alice's profile with Bob's <BA private key>
-  App B ->> Bob: Bob's app adds Alice to the list of connections
-  App B ->> Server B: "connection acknowledgement" message
-  Server B ->> Server A: "connection acknowledgement" message
-  Server A ->> App A: "connection acknowledgement" message
+  App B ->> Bob: Bob's app matches <BA public key hash> with <BA public key><br>and decrypts the Alice's profile with Bob's <BA private key>
+  App B ->> Bob: Bob's app shows Alice's profile and adds it to the connections<br>(as pending)
+  App B ->> Server B: App registers on Bob's servers <BA public key hash> associated with <A_BA server public keys> (for sender)
+
+  Note over Alice, Server B: Now only Alice's app can send messages for <BA public key hash> to Bob's servers<br>1) signed using <AB private key><br>2) encrypted using <BA public key><br>3) signed/encrypted using <A_BA server private/public keys>
+
+  Note over App B: App creates<br>"connection<br>acknowledged"
+
+  App B ->> Server A: Bob's app signs "connection acknowledged" with <BA private key>, encrypts it with <AB public key> and sends it to Alices's servers<br>{to: <AB public key hash>, message: <encrypted with AB public key>} (also signed/encrypted with B_AB server private/public keys)
+  Server A ->> App A: Alice's servers send to app "connection acknowledged"
   App A ->> Alice: Bob is now in the Alice's list of connections as "established"
+
+  Note over App A: App creates<br>"connection<br>acknowledged"
+
+  App A ->> Server B: Alice's app signs "connection acknowledged" with <AB private key>, encrypts it with <BA public key> and sends it to Bob's servers<br>{to: <BA public key hash>, message: <encrypted with BA public key>} (also signed/encrypted with A_BA server private/public keys)
+  Server B ->> App B: Bob's servers send to app "connection acknowledged"
+  App B ->> Bob: Alice is now in the Bob's list of connections as "established"
+
+  Note over Alice, Bob: Now Alice and Bob can exchange messages with each other, including key rotations and changes of servers they use<br>- Alice can send messages to Bob's servers to <BA public key hash> (Bob's servers allow Alice to send messages relying on A_BA keys)<br>- Bob can subscribe to messages on his servers sent to <BA public key hash> (Bob's servers allow Bob to receive messages relying on B_BA keys)<br><br>- Bob can send messages to Alice's servers to <AB public key hash> (Alice's servers allow Bob to send messages relying on B_AB keys)<br>- Alice can subscribe to messages on her servers sent to <AB public key hash> (ALice's servers allow Alice to receive messages relying on A_AB keys)