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* Gate connected-link trust on a secure session; deny forged direct announces the connected shortcut
Residual gap after the rotation-heal containment (#1401): "verified
direct" announces prove the signature but not directness — TTL is
unsigned — so a malicious connected peer can replay a victim's fresh
announce with its TTL restored. When the victim has no live link, the
replayer's link rebinds to the victim's ID and reads as "connected",
and MessageRouter's connected fast-path then trusts it outright: every
DM stalls on a Noise handshake the replayer can never complete and is
silently lost while showing "sent".
Router-level trust gate (no wire change):
- Transport gains canDeliverSecurely(to:) — BLE answers with an
established Noise session; Nostr keeps its prompt-delivery predicate;
the protocol default forwards to canDeliverPromptly for transports
without a forgeable link layer.
- MessageRouter.sendPrivate only trusts a connected link outright when
it can deliver securely; otherwise it still sends (kicking the
handshake on a genuine link) but retains a copy and hands a sealed
copy to couriers, like the reachable path. flushOutbox gets the same
gate so a flush over an insecure link resends instead of dropping the
retained copy.
Presence hardening (defense in depth): a "direct" announce arriving on
a link already bound to a different peer no longer shortcuts the
claimed peer into "connected" — only real link state does. Genuine
first-contact and direct announces are unaffected; only the ambiguous
heal path loses the forgeable shortcut.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
* Harden the insecure-link outbox bound; document the second-replay presence gap and the courier metadata tradeoff
Review follow-ups on the canDeliverSecurely gate:
- flushOutbox no longer counts connected-but-insecure flushes toward the
maxSendAttempts drop: the message was actually transmitted over a live
link, so a peer whose Noise handshake stalls across reconnect flapping
must not burn through the cap and lose the store-and-forward copy the
gate exists to preserve. Retention stays bounded by the 24h outbox TTL
and the per-peer FIFO cap; acks still clear it. Attempt-counting stays
for reachable-only (heuristic) sends. Regression test: >8 connected-
insecure flushes keep the retained copy, drop callback never fires.
- Document the known second-replay presence gap: linkBoundToOtherPeer
reads the binding before rebindLinkAfterVerifiedDirectAnnounce steals
the link, so once a first replay has rebound a link to an absent
victim's ID, a second replay marks the victim connected. Presence
display only — DMs stay on the retain+courier path via the router
gate. Not closed at the announce layer because the post-rebind state
is indistinguishable from a legitimate rotation/reconnect heal (a
supported, field-verified flow). Covered by a two-announce test.
- Note the accepted courier-spray metadata tradeoff at the connected-
insecure send: nearby verified peers receive a sealed copy (they learn
a DM exists, never its content), cleared on ack.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
* Promote a healed rotation to connected; normalize the secure-delivery probe; retain Codable properties in Periphery
Codex review follow-ups on 5017c232:
- P1: a legitimate rotation announce necessarily arrives on a link still
bound to the OLD peer ID, so the linkBoundToOtherPeer denial stored the
new identity as disconnected — and the rebind only fixed link state,
never the registry. A healed rotation then read as disconnected until
the peer happened to announce again. rebindLinkAfterVerifiedDirect-
Announce now promotes the rebound identity to connected after the
containment checks pass (registry markConnected + topology/snapshot/
peer-list refresh; the .peerConnected UI event already fired from the
announce path). This consciously moves the forged-presence residue
from second-replay to first-successful-rebind — bounded by the rebind
containment (never steals a live identity, one rebind per link per
cooldown) and still display-only: DMs stay gated on canDeliverSecurely.
Comments and the pinned tests updated; new regression test covers
rotate-on-open-link -> rebind -> isPeerConnected(new) == true.
- P2: BLEService.canDeliverSecurely probed the Noise session with the
peer ID as given, but sessions are keyed by the short wire ID — a send
keyed by the full 64-hex Noise key (favorites resolution) misread an
established session as insecure and needlessly retained + couriered
every DM until ack. Normalize with toShort() like isPeerConnected.
Test drives a real XX handshake and asserts both ID forms pass.
- Periphery: the PrekeyBundleStore.StoredBundle.noiseKey "assign-only"
flake fired again and slipped past its baselined USR (read exists in
loadFromDisk; the indexer intermittently misses it). Replace the
baseline entry with retain_codable_properties: true — deterministic,
and a truly-dead Codable field is a persisted-format change anyway.
Local periphery scan --strict: no unused code detected.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---------
Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <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.
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 persistent identifiers
- Private Message End-to-End Encryption: Noise Protocol for mesh, NIP-17 for Nostr
- 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
- 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
- NIP-17 Encryption: Gift-wrapped private messages for internet privacy
- Ephemeral Keys: Fresh cryptographic identity per geohash area
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
- NIP-17 gift-wrapping for privacy
- 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
cd bitchat
open bitchat.xcodeproj
To run on a device there're a few steps to prepare the code:
- Clone the local configs:
cp Configs/Local.xcconfig.example Configs/Local.xcconfig - Add your Developer Team ID into the newly created
Configs/Local.xcconfig- Bundle ID would be set to
chat.bitchat.<team_id>(unless you set to something else)
- Bundle ID would be set to
- Entitlements need to be updated manually (TODO: Automate):
- Search and replace
group.chat.bitchatwithgroup.<your_bundle_id>(e.g.group.chat.bitchat.ABC123)
- Search and replace
Option 2: Using just
brew install just
Want to try this on macos: just run will set it up and run from source.
Run just clean afterwards to restore things to original state for mobile app building and development.
Localization
- Base app resources live under
bitchat/Localization/Base.lproj/. Add new copy toLocalizable.stringsand plural rules toLocalizable.stringsdict. - Share extension strings are separate in
bitchatShareExtension/Localization/Base.lproj/Localizable.strings. - 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.