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.

bitchat.free

📲 App Store

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, /who style 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 level
  • neighborhood (6 chars): District/neighborhood
  • city (5 chars): City level
  • province (4 chars): State/province
  • region (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:

1. Bluetooth First (preferred when available)

   • Direct connection with established Noise session
   • Fastest and most private option

2. Nostr Fallback (when Bluetooth unavailable)

   • Uses recipient's Nostr public key
   • BitChat's app-specific private-envelope encryption
   • Routes through global relay network

3. 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 build to compile-check any localization updates.