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* Require signed sender for broadcast file transfers (#1406 follow-up) Broadcast file transfers trusted the packet's claimed senderID whenever the peer was merely connected (resolveKnownPeer allowConnectedUnverified: true), unlike public messages and public voice frames, which both require a valid packet signature from the claimed sender. Codex flagged the consequence on PR #1406: a peer that observed a public voice burst could broadcast a spoofed voice_<burstID>.m4a note under the talker's senderID, and ChatLiveVoiceCoordinator.absorbFinalizedVoiceNote would replace the signature-verified live bubble with attacker audio (senderPeerID + scope were the only bindings, both attacker-forgeable on this path). Bring broadcast file transfers up to the same bar as public messages: verify the packet signature against the registry signing key, falling back to the persisted-identity signature lookup, before trusting the sender. Directed (private) transfers keep the lenient connected-peer path — they are addressed to us specifically and carry no broadcast exposure. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Exempt self broadcasts from the file-transfer signature gate Review of #1407 caught a regression: our own broadcast files replayed via gossip sync arrive with ttl==0 (so isSelfEcho does not drop them) and cannot be verified against the peer registry or identity cache, so the new broadcast signature guard would drop them. Mirror BLEPublicMessageHandler's self exemption — self packets are trivially authentic — and add a regression test. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Stop relaying broadcast file packets that fail sender authentication Codex review on #1407: the new signature gate dropped spoofed broadcast files locally, but BLEService's .fileTransfer case still fell through to scheduleRelayIfNeeded, so a forged file kept propagating to downstream (possibly older, ungated) nodes. Have the handler report failed sender authentication and skip the relay step, like invalid board posts and voice frames. Local-only drops (malformed payload, quota, save failure) and files directed to other peers still relay unchanged. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Fix CI hang: sign the max-size reassembly file transfer, unhang timeouts Both CI runs on #1407 died at the 5-minute watchdog (SIGKILL, exit 137) with the test process fully idle. Root cause was a pair of issues in FragmentationTests: - "Max-sized file transfer survives reassembly" injected an UNSIGNED broadcast file from an unknown peer, which the new broadcast signature gate now drops by design. Sign the packet and preseed the sender's signing key, mirroring the public-message reassembly tests. - CaptureDelegate's wait helpers could never time out: the timeout task threw, but withThrowingTaskGroup then awaited the sibling child that was parked in a non-cancellable withCheckedContinuation, deadlocking the whole run (hang instead of a 5s failure). Resume the parked continuation from a cancellation handler so timeouts now fail fast. 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.