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 persistent identifiers
• Private Message End-to-End Encryption: Noise Protocol for mesh, NIP-17 for Nostr
• 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
• 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 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
   • NIP-17 gift-wrapping for privacy
   • 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

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)
• Entitlements need to be updated manually (TODO: Automate):
  • Search and replace group.chat.bitchat with group.<your_bundle_id> (e.g. group.chat.bitchat.ABC123)

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 to Localizable.strings and plural rules to Localizable.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 build to compile-check any localization updates.