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.
Install from the App Store, or build from source you have verified. A compiled build from anywhere else cannot be verified — see Verifying bitchat for how to check source against the per-release hash manifest, and for what to do if that is the only build you can get.
This matters more than it usually would: this repository has been the target of takedown demands, and when a repository or releases page disappears, mirrors appear that nobody can check.
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 on identity and metadata for what a nearby radio can observe
Overview
bitchat is a decentralized, privacy-first peer-to-peer messaging app written in Swift that combines a local Bluetooth LE mesh with an internet fallback using the Nostr protocol. The repo implements a dual-transport architecture: an offline Bluetooth mesh with multi-hop relay (up to 7 hops) and Noise-protocol end-to-end sessions, plus Nostr relays for global reach with location-based geohash channels and BitChat private-envelope encryption. The app is a universal native iOS/macOS client available on the App Store and buildable from source; the README includes concrete build/test workflows (Xcode schemes, swift test, and just commands) and a dedicated VERIFYING-A-BUILD.md for validating release binaries.
Why It Matters
Practical offline-first messaging: Bluetooth mesh multi-hop routing, compact binary packets, LZ4 compression and adaptive battery modes make it suitable for protests, disaster scenarios, and remote areas where internet is unavailable.
Privacy and resilience trade-offs are explicit: no accounts or phone numbers, Noise for live sessions, BitChat private envelopes over Nostr (proprietary — not NIP-17/44/59 compatible), and an emergency triple-tap wipe. The README warns users about takedown/mirror risks and provides a verification procedure for trusting builds.
Developer-friendly and auditable: full Swift source, Xcode project and SwiftPM tests, instructions for simulator runs and reproducible local builds, plus public-domain licensing to simplify reuse.
Who it's useful for
Privacy-conscious mobile users who need accountless local chat and optional global reach.
First responders, field teams, and organizers needing reliable offline mesh messaging.
Developers and researchers interested in hybrid transport, Bluetooth LE mesh design, and Nostr integration.
Why it's trending now
The project saw a large daily star surge and attention (2,346 stars today) driven by interest in decentralized offline-capable messaging and by community concern over takedown demands and mirrored releases; the repo's explicit build-verification guidance and App Store presence have amplified visibility and discussion.
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:
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:
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.