原文链接

bitchat

A secure, decentralized, peer-to-peer messaging app that works over Bluetooth mesh networks. No internet required, no servers, no phone numbers - just pure encrypted communication.

License

This project is released into the public domain. See the LICENSE file for details.

Features

• Decentralized Mesh Network: Automatic peer discovery and multi-hop message relay over Bluetooth LE
• End-to-End Encryption: X25519 key exchange + AES-256-GCM for private messages
• Channel-Based Chats: Topic-based group messaging with optional password protection
• Store & Forward: Messages cached for offline peers and delivered when they reconnect
• Privacy First: No accounts, no phone numbers, no persistent identifiers
• IRC-Style Commands: Familiar /join, /msg, /who style interface
• Message Retention: Optional channel-wide message saving controlled by channel owners
• Universal App: Native support for iOS and macOS
• Cover Traffic: Timing obfuscation and dummy messages for enhanced privacy
• Emergency Wipe: Triple-tap to instantly clear all data
• Performance Optimizations: LZ4 message compression, adaptive battery modes, and optimized networking

Setup

Option 1: Using XcodeGen (Recommended)

1. Install XcodeGen if you haven’t already:

   brew install xcodegen
   

2. Generate the Xcode project:

   cd bitchat
   xcodegen generate
   

3. Open the generated project:

   open bitchat.xcodeproj
   

Option 2: Using Swift Package Manager

1. Open the project in Xcode:

   cd bitchat
   open Package.swift
   

2. Select your target device and run

Option 3: Manual Xcode Project

1. Open Xcode and create a new iOS/macOS App
2. Copy all Swift files from the bitchat directory into your project
3. Update Info.plist with Bluetooth permissions
4. Set deployment target to iOS 16.0 / macOS 13.0

Usage

Basic Commands

• /j #channel - Join or create a channel
• /m @name message - Send a private message
• /w - List online users
• /channels - Show all discovered channels
• /block @name - Block a peer from messaging you
• /block - List all blocked peers
• /unblock @name - Unblock a peer
• /clear - Clear chat messages
• /pass [password] - Set/change channel password (owner only)
• /transfer @name - Transfer channel ownership
• /save - Toggle message retention for channel (owner only)

Getting Started

1. Launch bitchat on your device
2. Set your nickname (or use the auto-generated one)
3. You’ll automatically connect to nearby peers
4. Join a channel with /j #general or start chatting in public
5. Messages relay through the mesh network to reach distant peers

Channel Features

• Password Protection: Channel owners can set passwords with /pass
• Message Retention: Owners can enable mandatory message saving with /save
• @ Mentions: Use @nickname to mention users (with autocomplete)
• Ownership Transfer: Pass control to trusted users with /transfer

Security & Privacy

Encryption

• Private Messages: X25519 key exchange + AES-256-GCM encryption
• Channel Messages: Argon2id password derivation + AES-256-GCM
• Digital Signatures: Ed25519 for message authenticity
• Forward Secrecy: New key pairs generated each session

Privacy Features

• No Registration: No accounts, emails, or phone numbers required
• Ephemeral by Default: Messages exist only in device memory
• Cover Traffic: Random delays and dummy messages prevent traffic analysis
• Emergency Wipe: Triple-tap logo to instantly clear all data
• Local-First: Works completely offline, no servers involved

Performance & Efficiency

Message Compression

• LZ4 Compression: Automatic compression for messages >100 bytes
• 30-70% bandwidth savings on typical text messages
• Smart compression: Skips already-compressed data

Battery Optimization

• Adaptive Power Modes: Automatically adjusts based on battery level

  • Performance mode: Full features when charging or >60% battery
  • Balanced mode: Default operation (30-60% battery)
  • Power saver: Reduced scanning when <30% battery
  • Ultra-low power: Emergency mode when <10% battery

• Background efficiency: Automatic power saving when app backgrounded

• Configurable scanning: Duty cycle adapts to battery state

Network Efficiency

• Optimized Bloom filters: Faster duplicate detection with less memory
• Message aggregation: Batches small messages to reduce transmissions
• Adaptive connection limits: Adjusts peer connections based on power mode

Technical Architecture

Binary Protocol

bitchat uses an efficient binary protocol optimized for Bluetooth LE:

• Compact packet format with 1-byte type field
• TTL-based message routing (max 7 hops)
• Automatic fragmentation for large messages
• Message deduplication via unique IDs

Mesh Networking

• Each device acts as both client and peripheral
• Automatic peer discovery and connection management
• Store-and-forward for offline message delivery
• Adaptive duty cycling for battery optimization

For detailed protocol documentation, see the Technical Whitepaper.

Building for Production

1. Set your development team in project settings
2. Configure code signing
3. Archive and distribute through App Store or TestFlight

Android Compatibility

The protocol is designed to be platform-agnostic. An Android client can be built using:

• Bluetooth LE APIs
• Same packet structure and encryption
• Compatible service/characteristic UUIDs