README

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:

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

bash

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`