Bluetooth Transaction System

A decentralized Ethereum wallet system that enables offline transaction signing and Bluetooth-based transaction broadcasting with a relayer service.

Project Structure

bluetooth-txns/
├── wallet/                 # React Native mobile wallet app
│   ├── screens/           # App screens
│   │   ├── WalletSetupScreen.js
│   │   ├── HomeScreen.js
│   │   ├── SendScreen.js
│   │   └── ScanScreen.js
│   ├── utils/             # Utility functions
│   │   ├── db.js          # SQLite database operations
│   │   └── verifyAck.js   # Acknowledgement verification
│   ├── App.js             # Main app component
│   ├── index.js           # App entry point
│   └── package.json       # Dependencies and scripts
└── relayer/               # Node.js relayer server
    ├── index.js          # Express server with transaction relaying
    └── package.json      # Server dependencies

Features

Wallet App

• Wallet Management: Create new wallets or import existing ones
• Offline Operation: Sign transactions completely offline
• QR Code Support: Send and receive transactions via QR codes
• Transaction History: View complete transaction history with balances
• Secure Storage: Private keys stored securely using Expo Secure Store

Relayer Service

• Transaction Broadcasting: Relay signed transactions to Ethereum network
• Acknowledgement System: Provide signed transaction confirmations
• Balance Tracking: Track sender and receiver balances after transactions
• REST API: Simple HTTP endpoints for transaction processing

Technology Stack

Wallet (Mobile App)

• React Native with Expo framework
• Ethers.js for Ethereum operations
• SQLite for local data storage
• React Navigation for screen management
• Expo Camera/Barcode Scanner for QR code handling

Relayer (Server)

• Node.js with Express.js framework
• Ethers.js for Ethereum interactions
• CORS enabled for cross-origin requests
• Body-parser for request body parsing

Setup Instructions

Prerequisites

• Node.js (v16 or higher)
• npm or yarn
• Expo CLI (npm install -g expo-cli)
• Ethereum RPC endpoint (Infura, Alchemy, or local node)

Wallet Setup

1. Navigate to the wallet directory:

   cd wallet

2. Install dependencies:

   npm install

3. Start the development server:

   npm start

4. Use Expo Go app on your mobile device to scan the QR code and run the app

Relayer Setup

1. Navigate to the relayer directory:

   cd relayer

2. Install dependencies:

   npm install

3. Create a .env file with the following variables:

   RPC_URL=your_ethereum_rpc_url
   RELAYER_PRIVATE_KEY=your_relayer_wallet_private_key
   PORT=3000

4. Start the relayer server:

   node index.js

Usage

Creating a Wallet

1. Open the mobile app
2. Tap "Create New Wallet" to generate a new Ethereum wallet
3. Securely save your private key (displayed on screen)
4. Tap "Save and Continue" to proceed to the home screen

Sending a Transaction

1. From the home screen, tap "Send"
2. Enter the recipient address and amount
3. The app will generate a signed transaction (offline)
4. A QR code containing the signed transaction will be displayed
5. Use another device to scan the QR code and broadcast via the relayer

Receiving a Transaction

1. From the home screen, tap "Scan to Receive"
2. Scan a QR code containing a signed transaction
3. The app will verify the transaction and store it locally
4. The relayer will broadcast the transaction to the network

Relayer API

POST /relay

• Body: { "signedTx": "0x..." }
• Response: Transaction acknowledgement with signature

GET /

• Health check endpoint returns "Relayer service is running!"

Security Features

• Private keys never leave the device
• All transaction signing happens offline
• Relayer only broadcasts pre-signed transactions
• Acknowledgement signatures prevent tampering
• SQLite database encryption via Expo Secure Store

Development

Adding New Screens

1. Create new screen component in wallet/screens/
2. Add navigation route in wallet/App.js
3. Update navigation imports as needed

Extending Relayer Functionality

1. Add new endpoints to relayer/index.js
2. Update environment variables as needed
3. Test with Postman or curl commands

Troubleshooting

Common Issues

QR Code Scanning Not Working

• Ensure camera permissions are granted
• Check Expo Camera compatibility with your device

Relayer Connection Errors

• Verify RPC_URL in .env is correct
• Check relayer wallet has sufficient ETH for gas

Database Errors

• App may need to be restarted if database schema changes

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Test thoroughly
5. Submit a pull request

License

This project is licensed under the MIT License - see the LICENSE file for details.