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.

This is the Android implementation of bitchat, fully protocol-compatible with the iOS version for cross-platform mesh communication.

bitchat.free

GitHub Releases

See it in action

Offline mesh conversation	Geohash globe picker

License

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

Features

• Dual Transport Architecture: Bluetooth LE mesh for offline messaging, Nostr relays for internet-based messaging
• Location-Based Channels: Geographic chat rooms using geohash coordinates over Nostr relays
• Intelligent Message Routing: Automatically chooses the best transport, with queuing and retry when a peer is unreachable
• End-to-End Encryption: Noise Protocol (XX pattern, X25519 + ChaCha20-Poly1305) for private messages over the mesh
• Decentralized Mesh Network: Automatic peer discovery and multi-hop relay over Bluetooth LE (max 7 hops)
• Wi-Fi Aware Transport: Higher-bandwidth local mesh on supported devices
• Channel Chats: Topic-based group messaging with optional password protection (Argon2id + AES-256-GCM)
• IRC-Style Commands: Familiar /join, /msg, /who style interface
• Tor Support: Built-in Tor (Arti) for private internet connectivity
• Emergency Wipe: Triple-tap to instantly clear all data
• Cross-Platform: Binary protocol compatible with bitchat on iOS and macOS

Technical Architecture

Bluetooth Mesh Network (Offline)

• Direct peer-to-peer within Bluetooth range, multi-hop relay through nearby devices
• Noise Protocol sessions with forward secrecy; peer identities derived from static keys
• Compact binary packet format with fragmentation, TTL routing, and deduplication
• Adaptive duty cycling and connection limits for battery efficiency
• Foreground service keeps the mesh alive within Android background execution limits

Nostr Protocol (Internet)

• Global reach via public relays, geohash-based location channels
• Private messages fall back to Nostr for mutual favorites when the mesh is unavailable
• Ephemeral keys per geohash area

Android Stack

• Kotlin, Jetpack Compose (Material 3), MVVM
• Coroutines and Flow for all networking and state
• Core components: MeshForegroundService (persistent connectivity), BluetoothMeshService / WifiAwareMeshService (transports), UnifiedMeshService (transport selection), NoiseSessionManager (encryption sessions), MessageRouter (mesh/Nostr routing with outbox retry)

Building

Requires Android Studio and the Android SDK (API 26+).

git clone https://github.com/permissionlesstech/bitchat-android.git
cd bitchat-android
./gradlew assembleDebug

Install on a connected device:

adb install -r app/build/outputs/apk/debug/app-debug.apk

The app requests Bluetooth, location (required for BLE scanning), and notification permissions at runtime.

Release APKs and the Android App Bundle can be rebuilt byte-for-byte in the pinned Linux container. Maintainers should follow the Android release guide. See Reproducible builds for the build trust model and public GitHub/Google Play verification procedures.

Testing

# Unit tests
./gradlew test

# Lint
./gradlew lint

# Instrumented tests (requires a device or emulator)
./gradlew connectedAndroidTest

Note that BLE mesh behavior is difficult to emulate; protocol and session logic is covered by unit tests, while radio-level behavior needs real devices.