SecureBitchat

A hardened security fork of BitChat with production-ready security enhancements and private room support.

Overview

SecureBitchat is a security-hardened version of the decentralized Bluetooth mesh chat app BitChat. It maintains the core principles of offline BLE mesh communication, decentralized architecture, and P2P networking while implementing significant security improvements.

Core Security Enhancements

1. Buffer Overflow Protection

• Signature validation ensures data is at least 64 bytes before processing
• Safe null byte trimming prevents memory corruption
• Length validation on all variable-size fields

2. Payload Truncation (UInt16)

• Maximum payload size capped at 65,535 bytes
• Rejects packets exceeding the limit during encoding/decoding
• Prevents resource exhaustion attacks

3. Mentions DoS Protection

• Maximum 10 mentions per message
• Maximum 256 characters per mention
• Parsing with strict limits prevents algorithmic complexity attacks

4. Replay Attack Protection

• Timestamp validation within 24-hour window
• Nonce tracking for message uniqueness
• Ratchet key rotation prevents message replay

5. MITM Protection

• QR code based out-of-band fingerprint verification
• Biometric/PIN gate for sensitive operations
• Fingerprint verification before key exchange

6. Ephemeral Key Rotation

• Keys rotate every 1 hour or per session
• Forward secrecy maintained via Double Ratchet
• Automatic key rotation without user intervention

7. Forward Secrecy (Double Ratchet)

• libsodium-style Double Ratchet implementation
• Each message uses a unique encryption key
• Compromised keys don't affect past messages

8. Compression Leak Prevention

• Fixed-padding LZ4 compression
• Padding ensures uniform compressed output size
• Prevents traffic analysis via compression ratios

9. AEAD Encryption

• XChaCha20-Poly1305 for all packet encryption
• Authenticated encryption with additional data
• Nonce-based encryption prevents pattern detection

Private Rooms

Features

• Invite via Signed QR: Ed25519 signed invitations with expiration
• Argon2id Key Derivation: Password + room ID → encryption key
• MLS-style Ratchet: Group rekey when members join/leave
• Biometric/PIN Gate: Extra authentication for room access
• Traffic Padding: Uniform packet sizes hide metadata

Architecture

┌─────────────────────────────────────────────────────────────┐
│                    Private Room Manager                      │
├─────────────────────────────────────────────────────────────┤
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────────────┐  │
│  │  Create     │  │  Join       │  │  Rekey              │  │
│  │  Room       │  │  via QR     │  │  (on member change) │  │
│  └─────────────┘  └─────────────┘  └─────────────────────┘  │
│                                                              │
│  ┌─────────────────────────────────────────────────────────┐│
│  │              AES-GCM Encryption Layer                   ││
│  └─────────────────────────────────────────────────────────┘│
│                                                              │
│  ┌─────────────────────────────────────────────────────────┐│
│  │           Argon2id Key Derivation                       ││
│  │     password + roomId → 32-byte encryption key          ││
│  └─────────────────────────────────────────────────────────┘│
└─────────────────────────────────────────────────────────────┘

Building

Prerequisites

• Xcode 15+
• CocoaPods or Swift Package Manager
• iOS 16.0+ / macOS 13.0+

Using CocoaPods

cd SecureBitchat
pod install
xed .

Using Swift Package Manager

The project includes Swift Package Manager support for dependencies.

Testing

Run the test suite:

swift test

Or via Xcode:

xcodebuild test -scheme SecureBitchat -destination 'platform=iOS Simulator,name=iPhone 15'

Project Structure

SecureBitchat/
├── Sources/
│   └── SecureBitchat/
│       ├── Protocols/
│       │   └── SecureBinaryProtocol.swift   # Hardened protocol
│       ├── Security/
│       │   ├── SecureIdentityManager.swift  # Identity + MITM protection
│       │   └── SecureKeychainManager.swift  # Secure storage
│       ├── Ratchet/
│       │   └── RatchetService.swift         # Double Ratchet
│       ├── Rooms/
│       │   └── PrivateRoomManager.swift     # Private rooms
│       └── Crypto/
│           └── XChaCha20Poly1305AEAD.swift  # AEAD encryption
├── Tests/
│   └── SecureBitchatTests/
│       ├── SecureBinaryProtocolTests.swift
│       ├── PrivateRoomTests.swift
│       ├── RatchetServiceTests.swift
│       └── XChaCha20Poly1305Tests.swift
├── Docs/
│   └── diagrams.md                          # Flow diagrams
├── Podfile                                  # CocoaPods deps
└── README.md

Security Comparison

Feature	BitChat	SecureBitchat
Signature Validation	Basic	64-byte check
Payload Limit	4GB	65535 bytes
Timestamp Window	2 minutes	24 hours
Mentions Limit	None	10 max
Forward Secrecy	Noise only	Double Ratchet
Room Encryption	None	AES-GCM
Key Derivation	None	Argon2id
Biometric Auth	No	Yes
Traffic Padding	Optional	Always

License

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

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests for new functionality
5. Submit a pull request

Architecture Diagrams

See diagrams.md for Mermaid flowcharts showing:

• Secure room join flow
• Message encryption flow
• Key rotation sequence