spaced4ndyandspacedandy-agents-simplex
9696a71b91
* core, badge-service: name Apple claims by reference
Rename appleTransactionId to appleTransactionRef, matching googlePurchaseRef
and StoreTransactionRef. No behaviour change: the next change makes it
return a subscription's original transaction id, which the old name would
misstate.
Run: 001-badge-subscriptions, slice 1
* core, badge-service: store subscription charges and carry the subscription state
Add the service migration 20261012_badge_subscriptions: the subscription
charges table, the ledger's charge_id, and the payment's subscription state,
check time and Play token, replacing three subscription columns nothing
wrote. The ledger now stores and reads back charge credits, and the badge
credential response gains an optional subscription state that older clients
ignore and that reads an unknown state without failing. Nothing writes a
charge or a state yet, so no behaviour changes.
Run: 001-badge-subscriptions, slice 2
* core, badge-service: plan subscription charges and claim Apple subscriptions by original id
Add chargeEntries, the one planner for a store charge's ledger rows: a
lapse to the billing period start, the grant dated to that start, and a
lapse to now, so coverage follows the store's periods and every row
verifies by re-running it at its createdAt. A test runs its rows through
the client's own balanceChecked for first charges, monthly and annual
renewals, billing-retry recovery and grace.
An Apple auto-renewable transaction is now claimed by its original
transaction id, which every renewal keeps, so renewals resolve to one
purchase. One function names the ref for both the claim and the real
verifier, so they cannot disagree.
Run: 001-badge-subscriptions, slice 3a
* badge-service: credit a store subscription purchase
The catalog now tells subscription products from one-time ones and maps a
store plan to its tier and months. A subscription receipt is checked with
the store once: with a grantable charge, the service plans the charge's
rows from the store's period start, signs the first month, and writes the
payment, purchase, charge, ledger rows, issuance, state and Play token in
one transaction, answering with the subscription state. Without one, it
answers payment_pending (300 s while the period has not started or the
store is pending, a day otherwise), receipt_invalid for an ended Play
subscription, or test_purchase, and writes nothing. Replays carry the
state. The store verifier interface gains the subscription check, which no
real store implements yet; the fake store does.
Run: 001-badge-subscriptions, slice 3b
* badge-service: renew a subscription once its paid coverage ends
While a subscription purchase's coverage runs, issueBadge is unchanged
and makes no store call. Once it has ended, the service asks the store at
most once an hour per subscription, stamping every attempt, and answers
from the stored state in between; a failed check is retried after the
whole interval. A grantable charge is planned from the tip at the store's
period start, signed, and written with its issuance and state in one
transaction that re-reads the tip, answering internal if it moved. Any
other charge and the state are recorded without a ledger row. Every answer
for a subscription purchase carries its state.
Run: 001-badge-subscriptions, slice 4
* core: keep a subscription badge until the service says it ended
A purchase is a subscription exactly when its ledger replica holds a
charge credit, so the kind is derived with no column or migration. A
subscription is still asked about at zero months, at the shared weekly
moment, and keeps its badge past paidThrough until an answer says the
subscription ended, so a renewed month is presented at the old
credential's expiry with no gap, and a charge the store recovers later
still re-activates it. While it waits, the client records no failure and
raises no support-ended alert; "issued no credential" now fires only while
the ledger still owes a month. Prepaid purchases are unchanged.
Run: 001-badge-subscriptions, slice 5
* badge-service: check Apple subscriptions with the App Store Server API
With an in-app purchase key configured in [apple], the service reads a
subscription's status by its original transaction id from Get All
Subscription Statuses, authenticated by an ES256 token reused until near
expiry. Each signed transaction and renewal info is verified against the
pinned Apple root through the same chain check as one-time purchases, now a
separate function, and a body that fails it is a verifier failure, never a
refusal. Statuses map to renewing, cancelled, billing retry and ended;
family-shared transactions are refused; 401 and 403 are this service's
failure, other errors and timeouts unreachable. A verifier failure thrown
by a store check is answered internal, and a test subscription is refused
in one place for first purchases and renewals. Without the key, Apple
one-time purchases verify as before and subscriptions are not configured.
Run: 001-badge-subscriptions, slice 6
* badge-service: check and acknowledge Google Play subscriptions
The Play subscription check reads purchases.subscriptionsv2 by token
through the existing service-account client, with the same HTTP classes as
product reads, and maps Play's state, base plan, period, order id and
offer phase; the period start is its end minus the plan's length, and a
pending subscription stays pending. A subscription is acknowledged with
purchases.subscriptions.acknowledge before it is credited, skipped when
Play reports it acknowledged, so it never reaches the one-time endpoint.
Each store's subscriptions answer provider_not_configured when that store
is not configured. A charge on a plan the catalog does not sell is pending
rather than a malformed period.
Run: 001-badge-subscriptions, slice 7
* review: round 1 fixes
R1-1: test an App Store subscription renewal through issueBadge, including
a charge recorded before its period starts and granted later under the
same charge id.
R1-2: make the ledger's charge_id index unique, so the schema itself grants
each store charge at most once.
R1-3: pin that a charge on a plan the catalog does not sell, with an empty
period, is pending at purchase and recorded at renewal, never internal.
Run: 001-badge-subscriptions, review round 1
* core: update query plans
getBadgePurchase derives the purchase kind from the ledger replica, and a
subscription test makes a held store receipt due.
Run: 001-badge-subscriptions, final verification
* fixes
* core: move SubscriptionState to Badges.Types (structural)
BadgeState, which lives in Badges.Types, is about to carry a subscription's
state, and Badges.Service imports Badges.Types. Service re-exports it, as it
does BadgeServiceErrorCode. No behaviour change.
Run: 003-badge-subscriptions-ui, slice 1
* core: keep a store subscription's state on the client
The screens and alerts need to know whether a subscription renews, was
cancelled, waits for a charge, or ended, and the client dropped every state
the service sent but ended. It is now stored on the purchase: from the
answer to the first credit, and from a renewal answer only when the
asserted tip's coverage had ended, since while coverage runs the service
repeats what it read at the last renewal (a year old for an annual plan).
BadgeState gains `subscription` (the plan's months, from the latest charge
credit, and the state), and fills renewsAt/willRenew from it. A changed
state is announced with CEvtBadgeChanged. The column goes into the
unreleased M20260925 migration.
Run: 003-badge-subscriptions-ui, slice 2
* core: record the device store's view of a subscription
The service reads the store only once a subscription's paid coverage has
ended, so it never sees a cancellation while the period runs. The apps read
the device's store (StoreKit's renewal state, Play's isAutoRenewing) and
report it with /_badge subscription <state> <payment>, which records it on
the credited subscription purchase the payment resolves to and announces the
change to its owner.
A renewing report does not replace billingRetry or ended: Play lists a
subscription in its grace period with auto-renew on, and the service's next
answer clears billing retry once the charge lands.
Run: 003-badge-subscriptions-ui, slice 3
* core: claim a store-listed transaction only on the device that bought it
A store account's purchases are listed on every device signed into it:
Play's purchase query lists active subscriptions for their whole life, and
Apple's Transaction.updates delivers auto-renewables made on other devices.
A hand-over with no record and an unknown echoed invoice made a new record
under the presenting profile, so another device could claim a buyer's
subscription for its own active profile, or repeat a refused request every
30 days after cleanup.
/_badge purchase now takes a `listed` mark, which the apps' sweeps and
purchase listeners send: it joins only a record this core already has for
the transaction or its echoed invoice, and otherwise records and sends
nothing (CRStoreReceiptNotRecorded). The purchase call and Restore hand over
unmarked, as before.
Run: 003-badge-subscriptions-ui, slice 4
* core: let a held App Store subscription adopt its later transactions
A held Apple subscription record is keyed by its original transaction id,
so every renewal resolves to it. It kept the payment's back-off when a new
transaction arrived, and adopted any payment handed over, including a
revoked renewal, which the service refuses as receipt_invalid and so would
refuse the whole subscription.
A held Apple record now adopts a JWS only for another transaction with a
later purchaseDate and no revocationDate, read from the unverified payload,
and is then due at once with its retry delay and credit error cleared. A
re-delivered or re-signed copy changes nothing. A failed attempt writes its
back-off only if the record still holds the payment it sent.
Run: 003-badge-subscriptions-ui, slice 5
* core: refuse a badge code or invoice while a store receipt is pending
A code redeemed while a store receipt is held put the code's badge on the
profile, and the held receipt then waited behind it; for a subscription the
store kept charging every period meanwhile. Code redemption and invoice
creation now answer "store purchase open" while the profile holds an App
Store subscription receipt, or another receipt whose last failure can clear
on its own. A receipt that failed for good does not block, except an Apple
subscription, which Apple keeps charging; an uncredited Play subscription is
refunded by Play.
Run: 003-badge-subscriptions-ui, slice 6
* core: alert a subscriber that a payment failed, a renewal nears, or it was cancelled or ended
A subscription's alerts were the prepaid ones: a retired subscription said
"support ended", and nothing told the user a payment failed, an annual
renewal was near, or a cancelled subscription still runs. The derived alert
for a subscription is now, in order: subscription_ended once retired,
payment_issue while the store retries, issue_failed as before,
subscription_cancelled before paidThrough, and renewal_approaching from
three days before an annual plan renews, with a wake at that moment. Monthly
plans get no reminder, as there is no opt-out yet.
The unreleased migration's down step clears an acked subscription_cancelled,
which an older core cannot read.
Run: 003-badge-subscriptions-ui, slice 7
* badge-service: let the dev mock vouch for store subscriptions
With [dev] accept_unverified_store_receipts on, every subscription was
answered provider_not_configured, so the apps' subscription screens could
not be tried against a dev service. The mock now credits an App Store
subscription for the plan its product names, and a Play subscription for
the base plan a test token test.<basePlanId>.<uuid> names, or else its
product's monthly plan, from a minute ago; it remembers the plan in memory
and grants each renewal a new charge, answering a subscription it does not
know (after a restart) as ended.
The subscription check is given the product the presented receipt names,
which only the mock reads; it reads the service's badge clock at check time.
Run: 003-badge-subscriptions-ui, slice 8
* ios: hand App Store subscriptions to the core and report their renewal state
A subscription transaction was finished uncredited, so a buyer would pay and
get nothing. Every badge product now goes through a core invoice and is
handed over, and finished only once the core answers it credited or refused.
Transactions the store lists (the launch sweep, Transaction.updates) are
handed over as listed, so another device's purchase is not claimed here;
Restore purchases syncs with the App Store and claims them for this profile.
A revoked renewal is finished without hand-over, as the service would refuse
it and so the whole subscription.
The app reports StoreKit's renewal state to the core at each sweep, after the
manage-subscriptions sheet and after a restore. Monthly and annual are offered
only to an Apple ID with no earlier subscription in the group, which Apple
would fold a new one into.
Run: 003-badge-subscriptions-ui, slice 9
* ios: sell badge subscriptions and show their state on Your badge
Monthly and annual subscriptions are offered on How long and Check your
order, with the App Store's subscription disclosure, Terms of use and
Privacy policy links, and Restore purchases. Your badge shows a
subscription's state - Renews {date} · {price}, Ends {date}, Payment
problem, Renewing or Ended - with why another badge cannot be bought or
redeemed while it waits for its charge, Manage subscription and Restore
purchases. The chat list shows one banner for the current badge alert of
any kind: renewal soon, payment problem, cancelled, ended, as well as the
expired and renewal-failed ones it had.
Run: 003-badge-subscriptions-ui, slice 10
* android: hand Play subscriptions to the core and report their renewal state
The Kotlin port of the iOS store change. A Play subscription was
acknowledged uncredited; every badge product now goes through a core
invoice and is handed over. The sweep queries subscriptions as well as
one-time products, and the sweep and purchases listener hand over as listed,
so another device on the Google account does not claim them; Restore claims
them for this profile. A subscription is bought on its base plan's own
offer, and the app never acknowledges one itself: the service does when it
credits it, so Play still refunds one the service never credits.
The app reports Play's isAutoRenewing to the core as renewing or cancelled.
Run: 003-badge-subscriptions-ui, slice 11
* android, desktop: sell badge subscriptions and show their state on Your badge
The Kotlin port of the iOS screens. How long and Check your order offer
monthly and annual with Google Play's subscription disclosure, the privacy
policy link and Restore purchases. Your badge shows the subscription's state
with the same texts as iOS, the store named Google Play with a store lane and
"the store" without one, and Manage subscription and Restore purchases only
with a store lane on the local host. The chat list shows one banner for the
current badge alert of any kind. Desktop shows the state, footers and banners
without store rows or a price.
Run: 003-badge-subscriptions-ui, slice 12
* docs: describe the one badge alert banner in the apps' chat-list specs
Both chat-list specs described two hand-written badge banners (expired,
renewal failed); the chat list now has one banner for the current badge
alert of any kind. Also moves the line links this run shifted.
Run: 003-badge-subscriptions-ui, slice 13
* review: round 1 fixes
ios: stop selling a subscription once this device has seen one, so a
second profile is not charged for a subscription Apple folds into the
first (R1-12). Continue pins the chosen period on both apps (R1-13).
Only a device with a subscription asks its store for products and status
when reporting, and the purchases are marked checked before the report
(R1-14, R1-5: Kotlin now loads the products, so the price shows after a
restart). Restore says "Nothing to restore" after a cancelled purchase
(R1-7). Android keeps sweeping one-time purchases when the subscriptions
query fails (R1-6). The freshness comment in requestBadgeIssue states the
service's one-hour repeat of its last check (R1-1).
Run: 003-badge-subscriptions-ui, review round 1
* badge-service: answer a long-expired Play subscription as ended, and hash Play order ids
Play answers HTTP 410 for a subscription that expired too long ago to be
queried; it was read as unreachable, so the service never answered ended,
the badge was never retired and the profile stayed blocked from buying or
redeeming (R1-2). Play order ids appear on the buyer's receipt email, so
charges now store a hash of the order id, as purchase tokens already are
(R1-10).
Run: 004-badge-subscriptions-review, review round 1
* review: run 003 round 2 and run 004 round 1 app fixes
ios: buy a subscription only while it is still for sale, after re-reading
the Apple ID's transactions, and disable Pay once it is not, so a Check
your order screen opened before another profile or device subscribed
cannot buy one Apple folds into the earlier subscription (run 003 R2-1,
run 004 R1-4). android: skip the subscriptions query only on a device
whose Play does not support subscriptions, so Restore no longer says
"Nothing to restore" when the query failed (run 003 R2-2).
Run: 003-badge-subscriptions-ui round 2; 004-badge-subscriptions-review round 1
* review: round 3 fixes
ios: a subscription refused because this Apple ID subscribed before has
its own error, and Check your order says why Pay is disabled (R3-2).
android: skip the subscriptions query only when Play does not support
subscriptions, so a disconnected client fails the sweep or Restore
rather than reading as no subscriptions (R3-1).
Run: 003-badge-subscriptions-ui, review round 3
* core: update query plans
Regenerated by the full suite for the purchase, subscription status and adoption queries. Run: 003-badge-subscriptions-ui, final step
* badge-service: say what hashing the Play order id protects
The hash is unkeyed, so a holder of the buyer's receipt can still find the row (R2-1). Run: 004-badge-subscriptions-review, review round 2
* badge-service: name the rule for when a subscription is due a store check
The issue path's purchase read becomes getIssuePurchase and its "ask the
store now" test becomes subscriptionCheckDue, so the request router can
read the same rows by the same rule. No behaviour change.
Run: 005-subscriptions-load-timing, slice 1
* badge-service: answer every request that may ask a store on the store lane
App Store subscription purchases and subscription renewal checks called
their store from the main lane, so one slow or repeated store call held up
code redemptions and every other renewal. The router now reads the
purchase the way the issue path does and sends to the store lane every
request that may ask a store: Play purchases, App Store auto-renewable
purchases, and issue requests for a subscription due its store check,
judged a minute ahead so the handler never finds one due on the main lane.
Run: 005-subscriptions-load-timing, slice 2
* core: send no badge request before the wake a request that issued nothing set
While a subscription waited for its store charge, or a prepaid renewal
kept failing, every launch, foreground, profile switch and badge-state
read sent the issue request again, so the badge service saw the user's
app-open times for weeks. A due request now waits for the wake the last
pass stored, as long as that wake is no more than a stall interval away,
so it is asked again a day later as the renewal design says.
Run: 005-subscriptions-load-timing, slice 3
* fixup! core: send no badge request before the wake a request that issued nothing set
* fixup! badge-service: answer every request that may ask a store on the store lane
* badge-service: ask the App Store about a subscription purchase at most once an hour per claim
Anyone holding a real but uncreditable App Store subscription JWS, such as
their own lapsed subscription, could present it again and again, each time
spending an App Store Server API call from the quota every subscriber's
renewal check needs. The purchase path now remembers, in memory, which
subscription claims it asked about within the hour and answers a repeat
payment_pending with the time left. Keys are original transaction ids from
JWS that verified offline, entries expire after the hour, and a full table
asks rather than refuses, so memory stays bounded and no buyer waits on
another's claim.
Run: 005-subscriptions-load-timing, slice 4
* fixup! badge-service: ask the App Store about a subscription purchase at most once an hour per claim
* review: round 1 fixes
badge-service: a Play charge whose clipped period start leaves its month
already spent is answered as period over, not internal (R1-A1).
docs: the per-store answer classes list Play's 410 and the App Store
subscription check (R1-A2).
tests: a held receipt with no attempt yet blocks an invoice (R1-B2); a
renewing report keeps an ended status (R1-B3); a test comment names
[google] (run 005 C2-R2-1).
ios: a subscription refused because this Apple ID subscribed before
shows its sentence, not the error's name (R1-C2); ios, android, desktop:
the Check your order footnotes share one helper (R1-C3).
Run: 006-subscriptions-branch-review, review round 1
* fixup! review: round 1 fixes
* core: wait a day after a badge request that issued nothing, whatever the service or a snooze says
The hold on the stored wake let two moments the client does not schedule end it early. A renewal whose store check failed was answered with an hour's retryAfter, so the next activation after each hour sent it again, sampling when the app is opened. A snooze set before a request ended its wait at the snooze's end, timing the next request by the user's tap. Now a request that issued nothing waits the stall or a ledger moment: retryAfter only marks the failure transient, and a snooze is not a wake while a request waits; the request's own wake raises the alert again.
Run: 005-subscriptions-load-timing, slice 5
* fixup! review: round 1 fixes
* fixup! core: wait a day after a badge request that issued nothing, whatever the service or a snooze says
* badge-service: ask Play about a subscription purchase at most once an hour per token
The purchase path's hourly bound covered only App Store claims, so a re-presented Play subscription token, uncredited or credited to another key, spent a subscriptionsv2.get call each time, from the quota bucket Play renewal checks use. The bound now lives in purchaseSubscription, which both stores' purchase paths call, with one map per store: Play's keyed by the token's hash, so made-up Play tokens cannot fill the App Store's. Distinct made-up tokens are still one call each.
Run: 005-subscriptions-load-timing, slice 6
* badge-service: read Play's paused subscription as waiting to renew
An unmapped SUBSCRIPTION_STATE_PAUSED was answered internal, so a paused subscriber's renewal failed for the whole pause. Play reports a pause with auto-renewal on and charges again when it ends, so it now maps as an active subscription does: renewing, or cancelled with auto-renewal off. Pause is being turned off on the base plan; this is defence in depth. A pause grants nothing: Play names no new order, and the last one is already granted.
Run: 005-subscriptions-load-timing, slice 9
* core: retire a subscription badge once no store could still charge it, whatever the service answers
A subscription badge retired only on an ended answer, so a service that never sent one (a final error such as unknown_purchase_key, a rollback, a service that never answers) left the badge shown, one request a day forever, and the profile unable to redeem, buy or have a held receipt credited. Now it also retires once paidThrough is older than the longest store recovery window: Apple retries a failed renewal for up to 60 days, the longest with Play's pause off, plus a week. paidThrough counts every month the ledger holds, so banked months are never retired by it.
Run: 005-subscriptions-load-timing, slice 8
* ios, android: no Restore purchases on Your badge, where a restored purchase could not be credited
Your badge shows only while a badge is shown, so a purchase Restore found there with no record on this device was held under a profile whose held receipts are not processed while it shows a badge: not credited, nothing said, and on Android acknowledged, ending Play's three-day refund. Restore stays on Check your order, the one screen where a restored purchase can be processed.
Run: 005-subscriptions-load-timing, slice 7
* review: round 4 fixes
R4-1: a subscription badge is asked about first and retired only after the service answers, judged on the ledger after that answer. Retiring before asking used the client's paidThrough, which moves only when the client asks, so a subscriber who had not opened the app for longer than the recovery window while the store kept charging lost the badge at the next launch and was never asked again. A request that is not answered retires nothing. Tests: testSubscriptionRetiredAfterRecoveryWindow changed, testIdleSubscriptionKeptPastWindow and testSubscriptionNotRetiredWithoutAnswer added.
R4-2: one snooze comment where two contradicted each other.
R4-3: the recovery window's comment names Play's clipped period start.
R4-4: the retirement tests use subscriptionRecoveryWindow.
* badge-service: name the lane each request waits on
The router answered "may this request ask a store" as a Bool; renewal checks are to get a lane of their own, which a Bool cannot say. requestLane now names the lane: main, purchase or renewal. Both store lanes still share one queue, so no request changes lane.
Run: 007-subscriptions-retirement-lane, slice 1
* badge-service: check renewals on a lane no purchase waits on
Renewal checks shared the store lane with every purchase, so made-up Play tokens, which anyone can send, and the weekly burst of genuine purchases delayed them. Renewal checks now wait on a lane of their own, which only a request signed by the purchase key it names, and due its hourly store check, can reach.
Run: 007-subscriptions-retirement-lane, slice 2
* badge-service: name the web limiter's fixed-window step
takeToken counted a request against a minute's limit inline. The step becomes takeFrom, a pure function, so the purchase path's Play read allowance can use the same rule. No behaviour change.
Run: 007-subscriptions-retirement-lane, slice 3a
* badge-service: read Play's subscriptions at most 300 times a minute for purchases
A Play subscription purchase is asked about without any offline check, so any token in the accepted grammar spends a read from the Subscriptions quota renewal checks share. The purchase path now takes one of a minute's 300 reads for each Play subscription it asks about, a tenth of Play's default quota; with none left, the claim is answered rate_limited with the seconds left in the minute and is not held, as Play was not asked. A claim already held takes no read, and App Store claims, verified offline first, take none.
Run: 007-subscriptions-retirement-lane, slice 3
* core: count the subscription retirement window from the first answer that renewed nothing
The window was counted from the client's paidThrough, which moves only when the client asks, so after months away the first answer that granted nothing for any reason, a transient error, Play's clipped last days or a billing retry, retired a subscriber whose store may still have been charging. The purchase now stores its unrenewed run: the first answered request after which the ledger covered nothing, and the latest one. The badge retires once the window has passed since the run started, still only after an answer; a renewal ends the run, and an answer that comes a window or more after the latest one starts a new run, since an absence or an outage that long may hide a renewal. The window stays 67 days, written as Apple's 60-day billing retry plus the week contacts give an expired credential.
Run: 007-subscriptions-retirement-lane, slice 4
* review: round 1 fixes
R1-A1: the docs and the PlayReads comment said the purchase path reads Play's subscriptions at most 300 times a minute; it asks about at most 300 subscriptions, and a credited one is read once more to acknowledge it, so made-up tokens can spend at most a tenth of the quota renewal checks share.
R1-A2: a comment on RequestLane repeated the one above the queues.
R1-B1: a test that a held pass, which sends no request, leaves the unrenewed run unchanged.
R1-B2: the outage test's last wait for the run is 30 s instead of 5 s.
Run: 007-subscriptions-retirement-lane, review round 1
* core: add the badge subscription columns in their own migration
M20261016_badge_store_receipts shipped to master in #7587, so it must
stay as released. Restore it in both dialects and move the
subscription_status, unrenewed_since and last_unrenewed_at columns,
with the down step that clears subscription_cancelled acknowledgements
master cannot read, into M20261016_badge_subscriptions.
Run: 008-subs-migration-split, slice 1
* tests: drop the FilePath import a merge duplicated
The branch and master each added import System.FilePath ((</>)) to
Direct.hs on 2026-10-14 at different positions, and an earlier merge
kept both, so GHC warned that one was redundant. Keep master's.
Run: 008-subs-migration-split, slice 2
* fixup! core: add the badge subscription columns in their own migration
* ios, android, desktop: choose a badge in the app
* ios, android, desktop: use the dev badge page for testing (don't merge)
* update postgres schema
* update ios lib
* ios, android: hide Restore purchases on the order screen
* docs: summarize the badge subscriptions PR for reviewers, with diagrams
A summary of PR #7716 as built: buying, renewing and retiring on each
store, the retirement window, lanes and store limits, RPC, API and
database changes, alerts, tests, open items, and a review map. Seven
SVG diagrams, an HTML page with them inline, and a link from the plan.
* ios, android, desktop: restore purchases on the Support SimpleX screen
* ios, android, desktop: show the badge privacy policy in the app
* docs: keep only the badge subscription diagrams, with a README
The reviewer summary leaves the repo; the folder keeps the seven
diagrams with a README that captions each, and the plan links the
README.
* ios, android, desktop: smaller Restore purchases label
* ios: no alert when a badge purchase is cancelled
* docs: replace the badge subscriptions diagrams README with a short summary
A plain-English summary for anyone on the team, with the seven
diagrams and a self-contained HTML page; the plan links it again.
Diagrams follow the branch: Restore purchases is on Support SimpleX,
"Renewing" shows past paidThrough, and only a present retryAfter is
raised to an hour.
* ui
* ui wip
* core: retire a subscription badge as soon as its store says it ended
A subscription badge retired only on an ended answer to a request that was due, and only once the ledger's paidThrough had passed, so an ended answer while the ledger still covered, or the iOS app's report of StoreKit's expired or revoked state, left the badge shown, Support SimpleX unreachable and every purchase refused until a later request. Now an answered ended state is stored even while coverage runs (the service writes it only from a store check, after which it grants nothing), and every pass retires a subscription whose state, from this pass's answer or else as stored, is ended, whatever the ledger covers. The paidThrough guard stays at the prepaid call site, its only remaining user.
Run: 010-subscription-lifecycle, slice S1
* docs: record that a badge subscription cannot be restored or bought again
Restoring a subscription on a new device or under another profile fails for two independent reasons, the client's restore reading only unfinished transactions on iOS and the service answering any key but the one it credited receipt_used, and a lapsed iOS subscriber cannot subscribe again on the same install either. Both gaps files record it in their own format, and both restorePurchases() say why reading the store's entitlements alone would not help.
Run: 010-subscription-lifecycle, slice S2c
* fixup! core: retire a subscription badge as soon as its store says it ended
* transfer plan
* shorter plan
* update plan
* badge-service: let a dev deployment ask its mock store while coverage runs
[dev] check_store_during_coverage = on makes every issueBadge for a
subscription ask the dev mock, during paid coverage too, and bank the
month of a charge it can grant, issued once coverage reaches it. So a
renewal can be watched by hand without waiting a month, and a mock that
forgot the plan after a restart answers ended at once.
Off by default, and refused unless accept_unverified_store_receipts is
on, which is itself refused beside a real store: a real store has not
started its next charge while coverage runs, and asking spends the
quota every subscriber shares.
Run: 011-subscription-tools, slice S3a
* core: send a badge request at once from a build for the dev badge service
/_badge request <userId> sends the profile's badge request now, while
its badge is shown, and runs the badge pass on the answer, so a renewal
or an ended subscription can be watched by hand against the dev
service.
It is allowed only when ChatConfig's badgeDevRequests is set, which no
shipped build does and nothing sets at runtime: the dev-service branch
sets it beside its own badge service overrides. A request off the shared
expiry would tell requests apart, so every other build refuses it, and
it is refused from a paired remote controller.
Run: 011-subscription-tools, slice S3b
* fixup! badge-service: let a dev deployment ask its mock store while coverage runs
* fixup! badge-service: let a dev deployment ask its mock store while coverage runs
* fixup! core: send a badge request at once from a build for the dev badge service
* core: split the badge request's lock from its body
The receipt worker's attempt already holds the owner's badge lock, which is not reentrant, so it cannot call requestBadgeIssue. The body becomes sendBadgeIssue, and both answer a service error as Left (code, retryAfter) instead of Nothing, so that caller can classify it as it does today. No behaviour change.
Run: 011-subscription-resume, slice S2-0
* core: retire on a device's ended report only once the paid period is over
StoreKit can report a subscription expired during Apple's billing retry, and Apple may then recover the charge, so retiring at once on that report left a paying user without the badge. The service's answered ended still retires at once, also while the ledger covers. A stored ended, which is how the device's report arrives, retires once paidThrough has passed.
Run: 011-subscription-resume, slice S1c
* core: resume a retired Apple subscription when its store charges it again
A same-install resubscription keeps Apple's original transaction id, so its hand-over found the old credited record and was answered from it with the old credential: the subscriber paid and got nothing. A credited record is now held again when a later charge of its subscription is handed over, the charge is not revoked, its paid period runs and it is dated less than a day ahead of this device's clock, and the record's purchase is its owner's newest, a subscription and not shown, with no other receipt held. The receipt worker then sends the purchase's issueBadge, and the service grants the charge as a renewal. A covered answer shows the purchase again with the newest credential and clears an ended state. A charge the service answers without crediting is deferred an hour and refused a day after its purchase date, so it holds the profile for about a day. A refused resume is remembered on the record (every credit, re-hold and resume clears credit_error), so the app's sweep does not hold the same charge again after its day.
Run: 011-subscription-resume, slice S2a
* fixup! core: resume a retired Apple subscription when its store charges it again
Review round 1 fixes:
- R1-1: a resumable charge waiting behind another held receipt of the owner is answered held and left unfinished, rather than answered from the record and finished uncredited.
- R1-3: a resume shows the purchase again only with a credential that has not expired.
- R1-2, R1-8: tests of the resumable-charge rule and the hold's edge, of a held charge whose paid period ends before it is sent, and that a resumed profile shows the newest credential. The resume test is split in two, one environment each.
- R2-V1: a test comment that the reordered steps made false.
Run: 011-subscription-resume, review rounds 1 and 2
* core, ios, android, desktop: let a lapsed iOS subscriber subscribe again to the badge the profile retired
The iOS app refused any subscription to an Apple ID that ever subscribed, so a lapsed subscriber could never subscribe again in the app. Core now tells the apps each subscription's store reference (BadgeSubscription.transactionRef, optional in JSON), and the iOS gate opens a subscription card only when every earlier subscription of the Apple ID is the active profile's newest purchase, retired, of the card's badge: the one charge core resumes. Kotlin gets the model field only, as Play gives a resubscription a new token and needs no gate.
Run: 011-subscription-resume, slice S2b
* docs: bound a badge move by the previous credential's expiry
* badge-service: credit test purchases and check the store during coverage in a dev deployment
* core: let a dev build ask the badge service on an interval
* badge-service: log each request's command and each store check's outcome
* fix compilation
* badge-service: name the purchase each request came from in the log
* badge-service: name the purchase each request came from in the log
* core, ios, android: explain a failed badge renewal and stop retrying a subscription the store forgot; tests (#7788)
* core, badge-service, ios, android: change badge tier in the store, and restore a subscription on another device (#7795)
* core: tell the apps when a badge request banks a month without issuing it
A pass announced the badge state only when the balance start moved, so a charge granted onto running coverage, or a debit the service wrote, changed months left and paid-through without an event, and the apps kept showing the old renewal date until the screen was reopened. The pass now announces whenever the ledger's last entry is not the one it started from, which a moved balance start implies.
Run: 015-badge-fixes, slice 1
* core: test that every Play charge of a month-end subscription funds its month
Play reports only a period's end, and the service dates the charge a plan length before it, so month-end clipping could leave a charge funding less than its month. Walk a monthly and an annual Play plan anchored on 31 January through their renewals at the device's request moments, through the deployed Play verifier: each charge funds exactly its months, paid-through stays at most the grace behind Play's period end (three days at most in this walk), and no charge is left without a grant.
Run: 015-badge-fixes, slice 2
* core: test that the newest issued badge credential is taken by its ledger row
After a tier change the newer issuance can end before the older one, so ordering issuances by period end would answer the superseded credential to the worker and to the resume and tier-change paths. Pin the row order: the test fails if the query goes back to period_end order.
Run: 015-badge-fixes, slice 3
* review: round 1 fixes
The App Store tier-change hold, reviewed for the first time:
- R1-B2: a tier change's credit now shows its purchase again (shown_badge_id) in the same transaction, as a resume's does, so a retire that ran while the change was with the service cannot leave a paid purchase unshown and never renewed.
- R1-B5: a tier change of a shown purchase is held whatever other receipt is held, as the worker serves it while the badge is shown; only a resume waits for other held receipts.
- R1-B3: test a tier change the store does not vouch for: refused in silence, the badge kept, and answered from the record after.
- R1-B8: the changeTier comment names when the record settles.
Run: 015-badge-fixes, review round 1
* review: round 2 fixes
- R2-1: a granted tier change clears an ended state the device reported before it. A renewing report never replaces ended, and a charge of the new tier granted proves the subscription has not ended, so without this the worker retired the new tier's badge at its paid-through while the subscription renewed.
- R1-B3: test a tier change whose credential does not verify: the failure stays on the receipt record, not the purchase, and Supporter stays shown.
- R2-3: the refused tier change's test buys Supporter through an invoice, so it shows the refusal announces nothing.
- R2-2: the changeTier comment says what follows each way the record settles.
Run: 015-badge-fixes, review round 2
* review: round 3 fixes
- R3-1: a tier change whose answer says the subscription ended is not credited, as a resume is not, so the credit's clearing of a stored ended never drops the one this answer carries.
- R3-2: the changeTier comment in two lines.
Run: 015-badge-fixes, review round 3
* core: apply an App Store tier change at once only when it raises the tier
Apple keeps charging the old plan to the end of the period, so applying a downgrade at once took away a badge the subscriber had already paid for. A charge of another tier is now held and sent at once only from supporter to legend; a lower tier, or one that is not ranked (investor, unknown), is answered from the record and the renewal check grants it, as badges-rpc.md says. A record already held for such a change settles silently.
Run: 016-tier-change-direction
* core: test that an App Store change to a lower tier waits for the renewal
A Supporter charge handed over while Legend is shown is answered from the record and sends nothing, and the renewal check grants Supporter, shown once the Legend credential expires; a record an older build held for a lower tier settles with no request. Both fail if every change of tier is sent at once again.
Run: 016-tier-change-direction
* badge-service: let a restore ask the store without waiting for the purchase's own check
* docs: describe badge tier changes and restore as the service handles them
The RPC document splits a store tier change by store and direction: the
app never starts one, an App Store raise seen within a day of its charge
is sent as upgradeBadgeSubscription, every other change waits for the
renewal check, and a Play plan change is a new token, a new purchase.
transferBadge and its limits are checked against the handlers, and the
upgrades that are not built are marked so.
The overview admits what Restore discloses: the service links the two
purchase keys, a store receipt moves its subscription to whoever presents
it within the move limit, and a new badge or tier is shown as soon as it
is issued. The Android gap names what remains of Restore.
* docs: tell the badge subscriptions story with tier changes and restore
The summary now covers the whole lifecycle: buying, renewing, changing
tier, moving to another device or profile, and ending. The badge retires
as soon as the store says the subscription ended, a lapsed iOS subscriber
can resume the retired badge, an App Store raise is granted at once and
a lower tier at the renewal, and a Play plan change is a new purchase.
The known limits and the before-sale list follow the code.
The seven diagrams are updated, with stale file and line references
dropped, and two are added: a tier change and a restore. The page now
points at the diagram files instead of carrying copies of them.
* fixup! docs: describe badge tier changes and restore as the service handles them
* fixup! docs: tell the badge subscriptions story with tier changes and restore
* fixup! docs: describe badge tier changes and restore as the service handles them
* fixup! docs: tell the badge subscriptions story with tier changes and restore
* core: make the badge subscription tests fail on the defects they name (#7798)
* fix compilation
* fix api
* ios, android, desktop: open the badge page on the site again
* ios: choose a badge on the site, not in the app
* tests: hold the move with no charge to grant, not with the purchase's store check
* unfocus test
* update postgres schema
* badge-service: break a tie between issuances by their period, so both databases agree
* badge subscription review fixes (#7799)
* update badge subscriptions docs (#7802)
* core: show a changed badge tier to contacts as soon as it is granted
* update plans
* core: show a raised badge tier to contacts at once, hold back a lower one
* update sqlite schema
* badge subscriptions review fixes (#7903)
* update ios lib
* update query plans
* ios: one property wrapper on the chat view's chat (#7910)
* android: a shorter note under Restore purchases
* Revert "ios: one property wrapper on the chat view's chat (#7910)"
This reverts commit d5a24bb342.
* ci: larger RAM disk so tests do not run out of space
* update sqlite schema
* ios: preview references for the badge screens
---------
Co-authored-by: spacedandy-agents-simplex <342056592+spacedandy-agents-simplex@users.noreply.github.com>
29 KiB
Revision 2, 2026-10-22
SimpleX Supporter Badges
Table of contents
Introduction
The goal is for SimpleX Chat to be partly funded by its users, who buy supporter badges. A badge is shown on the profile of the person who bought it, and it raises the limits that other users and servers apply to that person's files. This document describes what a badge is, what it grants, how it is issued and presented, and what it discloses about the holder.
A badge is stored in the user's profile on the device, and it is presented as proofs that cannot be linked to each other or to the purchase. The SimpleX network has no accounts, and a paid feature must not introduce one: in other messengers a paid feature is attached to an account, and the operator sees in one record who paid and what they did with the feature.
What is a badge
A badge is a credential issued by the badge service, a bot operated by SimpleX Chat. The credential is a BBS signature over four values: a master key generated by the app; the expiry date; the badge type, currently supporter or legend; and a reserved field that is currently empty.
The holder of a BBS signature can prove that the issuer signed certain values, disclose some of those values, and keep the other values and the signature itself secret. The credential itself is therefore not sent to anyone. When the badge is to be shown or used, the app generates a proof that discloses the badge type, the expiry date and the reserved field, names the issuer key by its index, and hides the master key and the signature. Two proofs from the same credential cannot be linked to each other, by the issuer or by anyone else. Each proof is generated for one context, whether a conversation, a file or a session with a server, and is not accepted in any other.
The transport protocols of the network call the same credential an entitlement: a name, an expiry and an extra string, disclosed in a proof. The chat application puts the badge type into the name, so a server that verifies an entitlement and a contact who sees a badge are looking at different zero-knowledge proofs of the same credential.
What a badge grants
- A badge is shown on the profile to contacts, to the members of groups, and to the subscribers of channels.
- A badge allows larger files. The default limit is 1GB; a supporter can send files up to 2GB, and a legend up to 5GB. The limit is applied by the recipient, whose app verifies the sender's proof before it accepts a file above the default size.
- A badge extends the storage of files on servers. An XFTP server stores a file for 48 hours by default. It may be configured to store files for longer when they are uploaded by the holder of a badge of a given type; the example values in the server configuration file are 7 and 21 days for supporter and legend badge holders, respectively.
Two other uses are planned and described under Future work:
- A backup will be a link whose content the app replaces each time it makes a new backup, so that the same link restores the latest state. A badge will raise the size of the backup and the time it is stored, and the storage time is then the period the app can remain offline before the backup is lost.
- Servers that verify the proof will apply higher rate limits when creating messaging queues, file chunks and notification tokens.
What a badge discloses
The badge service holds the purchase key, the number of months bought, and the payment record of the purchase. A card payment is linked to the purchase, as in any other service; a user who wants the payment itself to be private may pay with cryptocurrency. In either case the record is held by the service alone, and the service does not learn where the badge is later shown or used, because a zero-knowledge proof contains nothing that refers back to the credential or the purchase.
An app store subscription's record is its store transaction, which renewals keep, and the charges the store reports for it. When Restore purchases, the app's command that hands the store's current subscriptions to the active profile, moves a subscription to another device or profile, the new purchase key presents the same store transaction as the old one, so the service links the two purchase keys, though not the profiles that hold them.
A party that verifies a proof learns the badge type and the expiry date. Since all credentials expiring in the same week have the same expiry date, these two values place the holder among the supporters whose badges expire that week.
Comparison with Signal badges
Signal sells donation badges using receipt credentials. The client obtains a credential against a payment without revealing its account, and then presents the credential once to the account server, which records its serial number, level and expiry against the account and attaches the badge to the account. The payment is not linked to the account cryptographically. The same mechanism is used for Signal's paid backups.
The differences follow from Signal having accounts and SimpleX not having them.
In Signal:
- The server holds the list of accounts that have badges.
- The credential can be verified only by the server that issued it.
- The credential is presented once, after which the badge is a property of the account.
- The client requests the credential and redeems it in a single sequence of jobs without delay, so the server can match the request made under the payment with the redemption made under the account by their times and by network address.
- The expiry of a credential is rounded up to the next day.
In SimpleX:
- A server verifies a proof for one session and cannot link that session to any other.
- A credential can be verified against the issuer's public key by contacts, channel relays and independently operated servers.
- A credential is presented every time the badge is shown or used, with a new proof each time.
- The request for a renewed credential and the profile update that presents it are made on different days.
- All credentials expiring in the same week have the same expiry.
| Property | Signal badges | SimpleX badges |
|---|---|---|
| Account required | Yes | No |
| Operator holds the list of badge holders | Yes | No |
| Verified by | The issuing server | Any party with the issuer's public key |
| Presentations per credential | One | Unlimited |
| Proof bound to the context of presentation | No | Yes |
| Expiry rounded up to | The next day | The end of the following Monday |
| Renewal and presentation on different days | No | Yes |
| Usable on independently operated servers | No | Yes |
Non-goals
- A badge does not restrict anything that is available today: the defaults are unchanged, and a badge only raises them.
- A badge does not create an identity: it has no persistent identifier, it is not linked across conversations, and an incognito profile does not show it.
- A badge cannot be transferred: a code can be redeemed once for each use it was issued with (usually one), and the credential obtained with it is usable only with the master key it was issued for. The exception is an app store subscription, which Restore moves to a new purchase key of whichever profile presents its store receipt, and moves again only once the last credential of the key it last moved from has expired.
- A badge does not exempt its holder from the limits a server applies: it lowers the cost of a resource without removing the limit on it.
- A badge cannot be revoked; credentials are issued for one month at a time instead.
Architecture
┌─────────────────┐ code ┌──────────────┐ purchase ┌──────────┐
│ Web purchase │ ────────> │ Holder │ ────────────> │ Issuer │
└─────────────────┘ │ (the app) │ <──────────── └──────────┘
└──────┬───────┘ credential
│ every month
│ a new proof each time
┌─────────────────────────┼───────────────────────┐
│ │ │
┌────▼─────┐ ┌─────▼──────┐ ┌─────▼──────┐
│ Contacts,│ │ File │ │ The user's │
│ groups, │ │ recipients │ │ own servers│
│ channels │ └────────────┘ └────────────┘
└──────────┘
Participants
- The issuer is the badge service, a bot on the SimpleX network with a contact address. It holds the secret key with which credentials are signed. Apps and servers hold a list of eight issuer public keys, and every credential includes the index of the key that signed it, so the service can move to the next key without a release of apps or servers.
- The holder is the app. It keeps the credential in the user's profile, generates proofs on the device, and renews the credential every month.
- The verifiers are contacts, group members, channel relays, the recipients of files, and the user's own servers. A verifier holds the issuer public keys and no other information about badges.
Service requests
The app and the badge service communicate through one-off service requests, a primitive of the SimpleX agent described in One-off requests to service addresses. Although the service has a contact address, it is not a contact of the app, and no conversation with it exists.
A request is a single message to the service's address. The app establishes a double ratchet, with post-quantum key agreement, from the keys published in the service's address link, encrypts the request with the double ratchet, and sends it to the address queue on the service's server in the same way as any message to a server chosen by another party, that is, through a proxy server when private routing is enabled (which is the default). With the request the app sends the address of a reply queue that it created for this request on one of its own servers. The service decrypts the request with a receiving ratchet initialised from its private keys, sends the reply to the reply queue under the same ratchet, and deletes its state; the app deletes the reply queue and the ratchet when it has the reply or when the request times out.
This exchange has the following properties:
- Unlike a request made directly to the service over HTTP, the app does not connect to the service, nor the service to the app. Each communicates only with SMP servers, so the service does not see the app's network address, and with private routing the service's server does not see it either.
- Unlike a chat connection, which is a persistent channel through which all requests made over it can be linked to each other, a service request does not create persistent state. Each request uses new keys and a new reply queue, so two requests from the same app cannot be linked by the service or by servers.
- A reply that decrypts proves that it came from the holder of the keys published in the service's link and signed by its root key, so a server cannot substitute a reply.
- The badge service answers a repeated request with the same result and does not execute the operation twice, so the app can repeat a request whose reply was lost.
A purchase is identified by an Ed25519 key pair that the app generates for it and does not use for any other purpose. Every request concerning the purchase, the redemption and each monthly renewal, is signed with this key, and the signature covers the request together with a value derived from the ratchet of that exchange, so it is valid for that exchange only and cannot be replayed. The agent verifies the signature and delivers the verified public key to the service with the request, and the service accepts a request about a purchase only when the verified key is the purchase key.
Buying and redeeming
A badge is bought for one or more months, either on the web or in the app.
On the web the purchase produces a code, which is then redeemed in the app. The code is the only data passed from the web site to the app: the web site does not learn which app redeems a code, and the app does not see the payment. The code is generated in the buyer's browser, and the service stores only its hash; at redemption the app presents the code itself, and the service matches it against the stored hash. A badge issued without a sale, for example in compensation for a problem, is a code generated by the operator, or by a moderator of the service's managed group, and redeemed in the same way.
In the app, the user pays by card, in cryptocurrency, or through the app store. The app requests an invoice from the service, or presents the receipt of the app store, and the service issues the credential once the payment is confirmed.
In both cases the app generates the master key and the purchase key pair before the purchase. To redeem a code, the app sends the code and the master key to the service, which issues the credential. A code redeemed a second time with the same purchase key returns its latest credential; a code redeemed with a different purchase key is refused once all its uses are taken.
Monthly issuance
A credential is issued for one month at a time, however many months were bought. The service keeps a count of the months remaining for each purchase key, and issues the next credential when the app asks for it. The months of an app store subscription are added as the store charges for them: the service asks the store before issuing each month, so a new charge funds the next month once the paid months have run out, and a refund or revocation the store reports while they run, as in an annual plan, ends the badge; it also asks at once when the app reports a higher tier, which it does for an App Store raise the device sees before the raised charge expires. The app asks about such a raise, or about a lapsed subscription its store charged again, a bounded number of times each time the device hands the charge over, and again after the next hand-over. Any other App Store change of tier is granted at the first check after the old plan's paid months run out, though Apple bills a raise at once. On Play another badge is a new purchase: the app starts no plan change, and Play's pages offered none for these products when tested; one made there would be a new purchase under a new token, credited only when Restore hands it over (see Upgrades). Unused months, e.g. if the app was offline, lapse at the next badge issuance.
Credentials are issued monthly to limit what the expiry date discloses. If credentials were issued for the whole term, a user who bought a year would hold a credential expiring on a day a year ahead, when few other credentials expire, and this date would be disclosed in every proof for a year. Instead, every credential is issued for one month, and its expiry is rounded to the end of the Monday following the end of the paid month (UTC). For example, if the paid month ends on Wednesday 14 October 2026, the credential expires at the end of Monday 19 October, and so does every credential whose month ends between Monday 12 and Sunday 18 October. All credentials whose paid month ends in the same week thus expire at the same instant.
The renewal is split over two days for the same reason. The app requests the next credential on the day before the current one expires, and when the current one expires, it switches to the new one and sends its updated profile to its contacts. In the example above, the app asks the service for the new credential on Monday 19 October and starts showing it on Tuesday 20 October, so an observer of both the request and the profile update cannot correlate them by time.
The renewal runs in the background and does not require any action from the user. Recipients accept a badge for seven days after its expiry, and servers for one day, so a renewal delayed by a few days is not visible to contacts.
Presentation
A BBS proof is generated over a string, called the presentation header, and is verified only against the same string. The string binds the proof to the context in which it is presented. Without it, a proof received in one conversation could be copied and presented in another. Between apps the string is sent with the proof, and the recipient checks that it is the string it expects; servers know the string already, so it is not sent to them.
The context of a conversation is the same string over which message signatures are computed:
- In a direct chat it is a hash derived from the state of the end-to-end encryption, which only the two sides hold.
- In a group it is the member's identifier together with the member's signing key.
- In a channel it is the channel's identifier together with the member's identifier, or the channel's identifier alone when a message is sent in the name of the channel.
A session with a server is identified by the TLS session identifier, which both sides derive from the TLS handshake and which differs on every connection.
Each time the app sends its profile, whether to a new contact, to a group it joins, or to everyone when the profile is updated, it generates a new proof and includes it. The proof is bound to the conversation in which the profile is sent: in a direct chat to the connection with the contact, in a group to the member's identity in that group, and in a channel to the member's identity established by the channel's roster. In a group the badge is accepted only from a message signed with the member's key, and in a channel it is verified against the key that the roster establishes for the member.
A file larger than the default limit is sent with two proofs. The first is placed in the file invitation, the message that announces the file, and is bound to the conversation and to the size of the file; the recipient's app verifies it when the invitation arrives. The second is placed in the file description, the record of where the chunks of the file are stored and how they are decrypted, and is bound in addition to a hash of the description and to the storage time of the file; the app verifies it before the download begins.
Servers
The client presents the entitlement proof in the transport handshake, bound to the TLS session identifier. The server verifies it once, when the session is established, and applies the result to every command in the session.
The client presents the proof only to its own servers, that is, to those configured for the profile, which are identified by the certificate fingerprint pinned in TLS. It does not present the proof to a server whose address it received from a contact or found in a file description, because a file description names the servers on which the chunks are stored, and these are chosen by the sender. If the app presented its proof to every server it connected to, a sender could store a file on a server of their own and learn, when the file is downloaded, that the person downloading it holds a badge.
On XFTP servers the proof extends the storage time of files. The server grants the smaller of the time requested by the client and the maximum configured for the badge type, and returns the resulting expiry. SMP servers and notification servers accept the same proof in their handshakes but do not yet make use of it.
The exchange between the app and the badge service, that is, the commands, responses and errors, is described in the badge service protocol.
Cryptographic primitives
Badges are built on BBS signatures, in the BLS12-381-SHA-256 suite, implemented by libbbs over blst. A credential is a signature over four values under the header SimpleX badges v1; a proof discloses three of them and is 304 bytes long. BBS was chosen for four properties that the design needs together:
- A proof can be verified by anyone who holds the issuer's public key, so contacts and independently operated servers verify badges without consulting the issuer.
- A proof discloses only the values selected.
- A proof cannot be linked to any other proof of the same credential.
- A proof is generated over a presentation header, so it can be bound to the context in which it is presented.
Credentials of the kind Signal uses can be verified only by their issuer, and a receipt credential discloses its serial number when presented, so it is presented once. Single-use tokens, such as blind signatures and the tokens of Privacy Pass, are likewise spent when presented and do not include values such as an expiry or a type.
Service requests are protected by the double ratchet of the SimpleX agent, with X448 key agreement and the sntrup761 KEM, established from keys published in the service's link. The purchase keys with which requests are signed, and the member keys that form part of the conversation context in groups, are Ed25519 keys. Codes are hashed with SHA-256, and the file description in the context of a file proof with SHA-512.
Security
Design objectives
- A proof discloses no value that links it to another proof or to the purchase.
- A proof used in one context, whether a session, a conversation or a file, cannot be used in another context.
- The timing of presentations does not identify the holder: all credentials expiring in the same week share the same expiry, and the renewal request and the profile update are made on different days. A new badge (after a purchase, a redemption, a Restore, or a store subscription resumed after it lapsed) is shown as soon as its credential is issued, so for these the request and the profile update are made together. A higher tier is shown as soon as it is issued too, whether the app reported it or a renewal check granted it, since the subscriber raised it in their store; a lower tier granted at a renewal check is shown when the current credential expires, as a renewal is.
- Requests to the badge service cannot be linked to each other, to a profile or to a network address, other than the redemptions of one multi-use code, the codes issued in the service's managed group or redeemed by its members, and a store subscription moved to a new key by Restore, which the service links to the key it moved from as the same store transaction funds both, and a request about a purchase can be made only by the holder of the purchase key.
- A credential cannot be forged: the issuer keys are fixed in apps and servers, and the app verifies a credential before storing it.
- A missing or failed proof leaves the default limit in place, and a server cannot be configured to grant a badge type less than the default.
Threat model
This threat model assumes the SimpleX network threat model and addresses the threats specific to badges.
The badge service
can:
- See the purchase key of every badge, the master key generated for it, the number of months bought, and the payment record.
- Issue any credential, or refuse to issue one, as it holds the issuer key.
- Link a code issued in its managed group to the member who asked for it and to that group, as the group's messages, codes included, are kept in the service's chat database.
- Link a redemption to a member of its managed group whose profile shows a new badge soon after it.
- Link the two purchase keys between which Restore moved a store subscription.
cannot:
- Connect a purchase with a profile, a contact, a group or a session with a server, other than a code issued in its managed group or redeemed by one of its members, as above - a proof contains nothing that refers back to the purchase.
- Learn where a badge is shown or used.
- Learn the network address of the app - requests reach the service through SMP servers, on connections created for the request.
A contact, a group member or a channel relay
can:
- See the badge type and the expiry date.
cannot:
- Tell whether a badge seen in another conversation belongs to the same person.
- Reuse a profile proof or a file proof in another context.
- Distinguish the holder from the other supporters whose badges expire in the same week.
A member of the badge service's managed group
can:
- Redeem any code issued in the group that is not revoked and has uses left, as every code is posted to the group.
- See when each use of a multi-use code was redeemed.
- Issue free codes of any type as a moderator or above, and revoke any code whose text they hold as an admin or above.
- Become the group's owner by being the first to join it, before an owner is set up.
- Guess who redeemed a code, when a member's profile shows a new badge soon after the code's message changes.
cannot:
- Redeem a revoked code, or a code with no uses left.
A server operator
can:
- See the badge type and the expiry date once in each session.
- Group together the sessions of the supporters whose badges expire in the same week.
cannot:
- Reuse the proof on another connection.
- Link a session to the purchase, to a profile or to sessions on other servers, except through the week of expiry.
- Obtain a proof from a client that does not use the server.
The server that hosts the badge service's address
can:
- See that requests arrive for the service.
cannot:
- See the content of requests.
- See the network address of the app when private routing is used.
- See the replies, which are sent to a queue on a server chosen by the app.
One badge on many machines
Since proofs are unlinkable, a server cannot count the sessions of a single credential, so the benefit granted by a badge must be limited without counting sessions. For this reason a badge lowers the cost of a resource without removing the limit on it, and limits per session remain in force.
Compromise of the user's device or backup
An attacker who obtains the credential and the purchase key can use the badge until it expires and renew it while months remain. There is no revocation, so the loss is limited to the months bought.
Interception of a code
A code is a bearer secret until its last use is taken; after that, it is refused to any other purchase key.
Interception of a store receipt
Restore moves a store subscription to any new purchase key that presents its store receipt, within the limit on moves, so whoever obtains the receipt can take the badge. The credential already issued on the device it left stays valid until it expires, and then Restore there can move it back. An App Store receipt stops moving the subscription once the store charges again, as only the subscription's latest transaction moves it. A Play purchase token stays the same across renewals, so it moves the subscription for as long as the subscription renews. Each move waits only for the last credential of the key the subscription moved from, so the receipt's holder and the user can take the badge from each other in turn.
A passive network observer
can:
- Observe SimpleX traffic between clients and servers.
cannot:
- See a proof - proofs to servers are inside TLS, in a handshake block of fixed size, and proofs to other users and requests to the badge service are inside end-to-end encrypted messages.
- Distinguish a session in which a proof was presented from a session without one.
Future work
- Backups will be stored on XFTP servers, and a badge will raise their size and their storage time, as described under What a badge grants.
- SMP servers and notification servers will verify the proof. A server that verifies it can charge the holder of a badge less for creating queues, file chunks and notification tokens (under the planned proof-of-work scheme, the required effort is divided by a factor configured for each badge type), and can apply higher rate limits and larger quotas.
- The transfer of a badge bought by card or cryptocurrency to a new device, and the pausing of a prepaid badge, are planned.