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* Bridge dedup keys on a content-derived stable mesh message ID Public mesh messages carry no message ID on the BLE wire, so every non-origin device minted a fresh UUID and the bridge's m-tag dedup only matched on the origin device: duplicate bridged rows, misattributed "across the bridge" counts, redundant downlink rebroadcasts, and an m-tag spoof vector (an attacker could claim a victim's message ID). Every device now derives the same stable ID from the signed wire fields (sender ID + ms timestamp + trimmed content, SHA256/32 hex) via the new MeshMessageIdentity — zero BLE wire change. The bridge event's m tag carries the origin coordinates ["m", senderIDHex, timestampMs] and receivers recompute the key from those plus the event's own content instead of trusting a claimed ID; old-format/absent tags fall back to the event ID as before. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Fix mixed-version message loss: m tag leads with the derived stable ID The previous layout (["m", senderIDHex, timestampMs]) broke v1.7.0 receivers: their parser takes m[1] unconditionally as the timeline dedup key whenever the tag has >= 2 elements, so every bridged message from a new-version sender keyed on the CONSTANT sender hex and inject-dedup dropped all but the first. The tag is now ["m", <derived stable ID>, senderIDHex, timestampMs]: old parsers get a per-message-unique m[1] (exactly today's semantics), while the new parser recomputes the ID from elements 2-3 plus the event's own content and never trusts element 1, keeping the recompute-don't-trust property. Also: - Soften the overstated security claim in MeshMessageIdentity and the BridgeService classify comment: forging a chosen ID onto different content is infeasible, but all three hash inputs are cleartext on the radio, so identical-content front-running by a radio-local attacker remains possible (no worse than the unbridged mesh). - Fix the stale archivedEchoKeys rationale: re-synced copies of others' messages now carry the derived stable ID (insert-by-ID catches them); the content key remains for echo--prefixed archive rows + self echoes. - Tests: old-parser semantics on the new tag (m[1] per-message-unique and equal to the derived ID) and a forged-m[1] event that cannot pre-poison a genuine message's dedup slot. 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.