Digital Cash System with Blind Signatures

This project implements a digital cash system similar to Chaum's blind signature scheme, demonstrating how to create, spend, and detect double-spending of digital coins while maintaining user privacy.

Features

• Blind signature implementation for secure coin creation
• Double-spending detection
• Merchant cheating detection
• Privacy-preserving transactions
• Identity revelation only for double-spenders

Prerequisites

• Node.js
• npm (Node Package Manager)

Installation

1. Clone the repository
2. Install dependencies:

npm install blind-signatures

Project Structure

• driver.js: Main execution file containing the core logic
• coin.js: Coin class implementation
• utils.js: Utility functions for cryptographic operations

How It Works

1. Coin Creation:

   • A user creates a coin with a specific amount
   • The coin contains blinded identity strings (RIS - Reveal Identity String)
   • The bank signs the blinded coin

2. Transaction Process:

   • User unblinds the signature
   • Merchant verifies the coin's signature
   • Merchant randomly selects left or right half of the identity string
   • Transaction is completed

3. Security Features:

   • Blind signatures ensure bank can't track coins
   • Double-spending detection reveals cheater's identity
   • Merchant cheating detection prevents RIS reuse

Usage

Run the demo:

node driver.js

Example Output

=== Digital Cash System Demo ===
Creating a new coin...
Created coin for: [User]
Amount: 20 units
Coin ID: [Unique ID]

=== Bank Operations ===
✓ Coin signed and unblinded successfully

=== Merchant Transactions ===
Merchant 1 accepting the coin...
✓ Transaction 1 completed

Merchant 2 accepting the same coin...
✓ Transaction 2 completed

=== Double-Spending Detection Results ===
🚫 ALERT: Double-Spending Detected!
Cheater Identity: [User]

Security Features

1. Privacy:

   • Regular users remain anonymous
   • Only double-spenders are identified

2. Anti-Fraud:

   • Double-spending detection
   • Merchant cheating detection
   • Secure blind signatures

3. Verification:

   • Bank signature verification
   • RIS validation
   • Transaction integrity checks

Technical Details

• Uses RSA blind signatures
• Implements one-time pad (OTP) for identity strings
• SHA-256 hashing for security
• 2048-bit key length for bank signatures

Contributing

Feel free to submit issues and enhancement requests!