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* Cohere per-link Noise auth and rebind containment into BLELinkAuthState The authenticated-link owners, the reconnect revalidation policy, and the two rebind-containment cooldowns were four loose bleQueue-owned maps whose invariants lived in call-site discipline: every teardown path had to remember to retire the proof AND close the revalidation epoch (the pair appeared seven times), and both cooldowns hand-rolled the same prune-check-record dance. BLELinkAuthState owns them as whole transitions — retireLink, retireLinks(ownedBy:), permitRebind, permitRedundantRetirement — with the ownership question (bleQueue today, engine after the option-B flip) answered in one place. No behavior change; the one call-site reordering (redundant retirement computes the survivor before the cooldown check instead of after) is outcome-equivalent since the cooldown only ever recorded when a survivor existed. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Split identity-link bindings out of the physical link store BLELinkStateStore owned two different kinds of truth: what physical links exist (CB handles, connect lifecycles, characteristics, stream assemblers) and who each link belongs to (peer bindings in both roles plus the preferred-peripheral reverse map for directed sends and fanout collapse). The bindings now live on BLELinkBindings — same bleQueue ownership, whole-transition methods, direct tests for the rotation reverse-map cleanup and the preferred-link survivor repair that were previously only exercised end to end. Composed operations that need both truths (remove-with-repair, direct link state, the subscribed- central snapshot, bind-only-live-links) live on the transport as explicitly bleQueue-confined helpers. This is the structural half of the option-B boundary flip (docs/BLE-ARCHITECTURE-V3.md): ownership of the bindings can now move to the engine without touching what-links-exist. An audit of every physical clear/remove found three sites (emergency clear, both unauthorized branches) that needed explicit binding-clear pairing under the split — each now clears both. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Fix iOS-gated constructors and preserve containment cooldowns on reset CI caught what the macOS SwiftPM build cannot see: two #if os(iOS) sites still passed the peerID field that slice B1 removed from BLEPeripheralLinkState (willRestoreState in BLEService and armPendingBackgroundConnects in BLERadioController). Both fixed and verified with a local iOS simulator xcodebuild. Codex also caught a real regression: BLELinkAuthState.removeAll() cleared the rebind/retirement cooldown maps, which the original panic and emergency reset paths deliberately left alive. A stable CoreBluetooth UUID must not earn a fresh rebind allowance just because the session state around it was wiped. removeAll() now clears only the proofs and revalidation epochs, and BLELinkAuthStateTests pins the survival invariant along with the other auth-state transitions. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Link layer slice 3: the option-B domain flip — bindings and link-auth move to the engine The identity domain (BLELinkBindings + BLELinkAuthState) is now owned by the engine queue, with a DEBUG dispatchPrecondition trapping any access from another queue. bleQueue keeps only physical link state. What changed shape: - Receive path is sans-I/O: bleQueue decodes frames and hands (packet, linkID) up through ingestDecodedPacket (panic lifecycle captured at the handoff); attributeAndHandlePacket resolves the sender binding, rejects spoofed senders, applies raw-announce binding, and records ingress on the engine. Per-link frame order is preserved end to end (both queues serial), which supersedes the old batch-local TOCTOU binding in the notification path. - The rotation rebind is one engine slot: containment checks, proof retirement, binding flip, reconnect decision, and rotated-identity retirement run straight-line; only CoreBluetooth cancels hop to bleQueue. The engine->bleQueue->engine ping-pong is gone, along with the _test_afterVerifiedDirectRebindEnqueued pause hook — the test that used it now asserts the atomicity directly (a paused engine wedged the old gate design into a three-queue deadlock). - Authenticated-send eligibility (notifyOrEnqueueIfAccepted, writeOrEnqueueIfAccepted) is checked on the engine, serialized against rebinds by construction; only physical admission (updateValue/write/backpressure) runs on bleQueue. - Teardown splits into discardPeripheralLinkPhysical (bleQueue, inline in the delegates) + retirePeripheralLinkIdentity (engine hop with survivor repair reading liveness via readLinkState). A binding can briefly outlive its physical link; liveness queries join against the physical store and the queued retirement converges the two. - Gossip delegate sends enter the engine via onEngine — safe because mesh.sync sits above the engine in the sync order (production engine code only async-dispatches into the manager). - checkPeerConnectivity rides an engine slot from the bleQueue maintenance tick. No wire changes. 1,974 tests green (parallel and serial), iOS simulator build clean, Periphery clean. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Link layer slice 4: deterministic multi-node mesh simulation — and the panic-announce bug it caught SimulatedMesh wires real CoreBluetooth-free BLEService engines edge-to-edge through the outbound packet tap and _test_ingestFrame (the production attribution path the B2 flip created), with per-edge synthetic link IDs and manual-scheduler time. Five multi-node tests run in ~40ms with no wall-clock waits: - announce exchange binds simulated links and connects peers - Noise sessions establish end-to-end (real crypto, both directions) - a public message relays across a line topology inside a TTL/frame budget (storm bound asserted) - an 8x duplicate flood delivers exactly once - a panic rotation rebinds the survivor's link exactly once and stays — the scenario that previously needed two phones and log archaeology Fidelity boundary (documented in the harness): no physical links, so fanout planning and backpressure are not exercised; attribution, binding, dedup, TTL, relay decisions, and sessions are the real engine code. The simulator found a real bug on its first run: the forced-announce throttle's lastSent survived a panic, so a rotation within bleForceAnnounceMinIntervalSeconds of the last announce silently swallowed the new identity's announce — leaving it invisible to the mesh until the next maintenance cycle. Today's device test only passed because the previous announce happened to be minutes old. BLEAnnounceThrottle gains reset(), called from the panic slot so the rotated identity owes no throttle debt; pinned by a unit test and the mesh rotation test. New DEBUG seams: _test_ingestFrame (production ingress attribution), _test_forceAnnounce, _test_fenceEngine. 1,980 tests green, Periphery clean, iOS simulator build clean. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Link layer slice 5: name the port — BLELinkEvent, one engine entry, delegates in their own files The upward half of the link-layer port is now a type. BLELinkEvent enumerates everything the bleQueue link layer tells the engine: frameDecoded plus the four physical lifecycle transitions (peripheralLinkEnded, centralLinkEnded, allPeripheralLinksEnded, allCentralLinksEnded). Every bleQueue→engine crossing goes through emitLinkEvent into one engine consumer (handleLinkEvent) — the scattered messageQueue.async identity hops in the delegates collapse into event emission, and the engine-side retirement/bookkeeping logic now lives in one switch. The CoreBluetooth delegate extensions move to their own files as physical bookkeeping plus event emission: - BLEService+LinkLayerCentralRole.swift (CBCentralManagerDelegate + CBPeripheralDelegate) - BLEService+LinkLayerPeripheralRole.swift (CBPeripheralManagerDelegate + write accumulation) BLEService.swift drops from 7,836 to ~7,100 lines. The physical-domain members the role files share flip private→internal; the queue contract is enforced by the existing DEBUG traps and grep guards, not access control. (Two of the flips — isAppActive, logBluetoothStatus — only surfaced on the iOS build; macOS SwiftPM cannot see #if os(iOS) code. Verified with a local iOS simulator build.) The simulated mesh now drives lifecycle events through the identical enum a radio does: linkDropEventRetiresBindingAndReconnectHeals covers drop → identity retirement → last-link peer bookkeeping → re-announce heal, entirely through the port. New seam _test_resetAnnounceThrottle models elapsed wall-clock for the throttle (deliberately separate from _test_forceAnnounce so the panic-rotation test keeps its regression value: the production panic path must do its own reset). The panic test's containment re-announces reset throttles explicitly so those assertions exercise real delivered announces instead of silently throttled ones. noiseSessionEstablishesEndToEnd gains a bounded scheduler-time settle loop after a one-in-many parallel-suite flake (no wall-clock waits). Deliberately not done (recorded in docs/BLE-ARCHITECTURE-V3.md): a formal handle(event)->[Effect] system and further engine-domain file splits — both would flip the engine's private state to internal for cosmetic file counts; the effect formalization rides future feature- module extractions instead. 1,981 tests green, Periphery clean, iOS simulator build clean. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Baseline logBluetoothStatus for the macOS Periphery scan Its callers are all inside #if os(iOS) (willRestoreState in both role files plus the app-state handlers), so the macOS-scheme scan sees the now-internal declaration with zero callers — the same class as the baselined candidateCount. Verified 1-USR diff; the previously private mangled variant was already baselined, which is why the pre-split scan never flagged it. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Fix #1538: release stale bindings on rotation instead of leaving a ghost With two live links to one phone, a panic rotation healed only the link the verified announce arrived on. The second link kept its binding to the retired identity, so that dead ID stayed in the peer list — and was kept alive by the NEW identity's own traffic, since a bound link attributes non-announce frames to its bound peer. It only healed when the stale link physically dropped. The issue proposed exempting the containment rule via retiredBy[X] = Y so the second link could rebind. Two problems: the exemption's stated precondition (X removed by retireRotatedPeer) can never hold in this scenario — the retire is gated on X having no remaining links, which is false precisely because the stale link exists — and it would loosen a security rule to fix a liveness bug. Instead the rotation now RELEASES every link still bound to the rotated-away identity (unbind + retire that link's Noise proof) and retires the identity. No containment rule changes: unbinding is strictly less trusting than any binding, and it is correct under both readings of a second link bound to the retired ID — same physical device (the field case), or one link is a spoofer holding a forged binding, since a peer ID is a Noise-key fingerprint and two devices cannot both legitimately own it. Released links reconverge through the ordinary unbound-link path: the next raw direct announce binds them to whoever they actually carry. Reproduced and fixed under the slice-4 simulator, which is why this lands as tests rather than another two-phone session: - duplicateLinkPanicRotationLeavesNoGhostAndHealsBothLinks fails without the fix (ghost in both knownPeers and getConnectedPeers, duplicate link still bound to the dead ID) - replayedVerifiedAnnounceCannotStealALinkOrEvictTheVictim pins the #1401 containment rule against exactly the attack this fix had to avoid re-opening, with a positive control proving the refusal is the containment check and not duplicate suppression Harness gains connectDuplicateLinks (two links to one peer, modelled in the central role — the links we cannot cancel, and the only role whose bindings a CB-free harness can form), silence (range loss without a link event, so a packet can be captured that the far side never saw), and emittedPackets (the attacker's capture buffer). Residual, documented at the fix: an attacker who binds their own link to X by replaying X's raw announce can drive a rebind there and so evict X's registry entry; X's next announce restores it, and the per-link rebind cooldown bounds the rate. This is the same class of capability the containment already accepts, not a new one. 1,983 tests green, Periphery clean, iOS simulator build clean. Closes #1538 Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> --------- Co-authored-by: jack <jackjackbits@users.noreply.github.com> Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
bitchat
A decentralized peer-to-peer messaging app with dual transport architecture: local Bluetooth mesh networks for offline communication and internet-based Nostr protocol for global reach. No accounts, no phone numbers, no central servers. It's the side-groupchat.
Getting a copy you can trust
Install from the App Store, or build from source you have verified. A compiled build from anywhere else cannot be verified — see Verifying bitchat for how to check source against the per-release hash manifest, and for what to do if that is the only build you can get.
This matters more than it usually would: this repository has been the target of takedown demands, and when a repository or releases page disappears, mirrors appear that nobody can check.
License
This project is released into the public domain. See the LICENSE file for details.
Features
- Dual Transport Architecture: Bluetooth mesh for offline + Nostr protocol for internet-based messaging
- Location-Based Channels: Geographic chat rooms using geohash coordinates over global Nostr relays
- Intelligent Message Routing: Automatically chooses best transport (Bluetooth → Nostr fallback)
- Decentralized Mesh Network: Automatic peer discovery and multi-hop message relay over Bluetooth LE
- Privacy First: No accounts, no phone numbers, no servers. Note that the mesh does use a persistent per-device identifier derived from your identity key — see the whitepaper on identity and metadata for what a nearby radio can observe
- Private Message End-to-End Encryption: Noise Protocol for mesh, BitChat private envelopes for Nostr fallback
- IRC-Style Commands: Familiar
/slap,/msg,/whostyle interface - Universal App: Native support for iOS and macOS
- Emergency Wipe: Triple-tap to instantly clear all data
- Performance Optimizations: LZ4 message compression, adaptive battery modes, and optimized networking
Technical Architecture
BitChat uses a hybrid messaging architecture with two complementary transport layers:
Bluetooth Mesh Network (Offline)
- Local Communication: Direct peer-to-peer within Bluetooth range
- Multi-hop Relay: Messages route through nearby devices (max 7 hops)
- No Internet Required: Works completely offline in disaster scenarios
- Noise Protocol Encryption: End-to-end encryption, with forward secrecy for live sessions (store-and-forward mail is sealed without it — see the whitepaper)
- Binary Protocol: Compact packet format optimized for Bluetooth LE constraints
- Automatic Discovery: Peer discovery and connection management
- Adaptive Power: Battery-optimized duty cycling
Nostr Protocol (Internet)
- Global Reach: Connect with users worldwide via internet relays
- Location Channels: Geographic chat rooms using geohash coordinates
- 290+ Relay Network: Distributed across the globe for reliability
- BitChat Private Envelopes: App-specific encrypted private messages over Nostr relays
- Ephemeral Keys: Fresh cryptographic identity per geohash area
BitChat's private-envelope format is proprietary and is not NIP-17,
NIP-44, or NIP-59 compatible. It uses Nostr as a relay transport but only
interoperates with BitChat clients: private payloads travel inside kind-1059
events whose v2:-prefixed content is a BitChat-specific XChaCha20-Poly1305
construction, not NIP-44 encryption.
Channel Types
mesh #bluetooth
- Transport: Bluetooth Low Energy mesh network
- Scope: Local devices within multi-hop range
- Internet: Not required
- Use Case: Offline communication, protests, disasters, remote areas
Location Channels (block #dr5rsj7, neighborhood #dr5rs, country #dr)
- Transport: Nostr protocol over internet
- Scope: Geographic areas defined by geohash precision
block(7 chars): City block levelneighborhood(6 chars): District/neighborhoodcity(5 chars): City levelprovince(4 chars): State/provinceregion(2 chars): Country/large region
- Internet: Required (connects to Nostr relays)
- Use Case: Location-based community chat, local events, regional discussions
Direct Message Routing
Private messages use intelligent transport selection:
-
Bluetooth First (preferred when available)
- Direct connection with established Noise session
- Fastest and most private option
-
Nostr Fallback (when Bluetooth unavailable)
- Uses recipient's Nostr public key
- BitChat's app-specific private-envelope encryption
- Routes through global relay network
-
Smart Queuing (when neither available)
- Messages queued until transport becomes available
- Automatic delivery when connection established
For detailed protocol documentation, see the Technical Whitepaper.
Setup
Option 1: Using Xcode
open bitchat.xcodeproj
For a signed device build, create your ignored local configuration and replace the example team ID with your Apple Developer Team ID:
cp Configs/Local.xcconfig.example Configs/Local.xcconfig
Local.xcconfig.example derives unique app and App Group identifiers from that
team ID. The entitlement files already reference $(APP_GROUP_ID), so tracked
project or entitlement files do not need to be edited.
Useful command-line checks from the repository root:
# macOS Debug build without signing
xcodebuild -project bitchat.xcodeproj -scheme "bitchat (macOS)" \
-configuration Debug CODE_SIGNING_ALLOWED=NO build
# Full SwiftPM test suite
swift test
# iOS simulator tests
xcodebuild -project bitchat.xcodeproj -scheme "bitchat (iOS)" \
-sdk iphonesimulator \
-destination 'platform=iOS Simulator,name=iPhone 17' test
If iPhone 17 is unavailable, choose an installed simulator from:
xcodebuild -showdestinations -project bitchat.xcodeproj -scheme "bitchat (iOS)"
Option 2: Using just
brew install just
just check
just run
just build and just run use the current bitchat (macOS) scheme and keep
Xcode output in the ignored .DerivedData/ directory. They never patch source,
project, configuration, or entitlement files.
just clean removes only .DerivedData/ and .build/. It does not invoke Git
or restore tracked files, so uncommitted work is preserved. just test runs the
SwiftPM suite and just test-ios runs the iPhone 17 simulator suite.
Localization
- App localizations live in
bitchat/Localizable.xcstrings. - Share extension strings are separate in
bitchatShareExtension/Localization/Localizable.xcstrings. - Prefer keys that describe intent (
app_info.features.offline.title) and reuse existing ones where possible. - Run
xcodebuild -project bitchat.xcodeproj -scheme "bitchat (macOS)" -configuration Debug CODE_SIGNING_ALLOWED=NO buildto compile-check any localization updates.