eCash Protocol Server

Production-grade backend API server implementing the eCash blind signature protocol.

Architecture

• Framework: Axum (async Rust web framework)
• Database: PostgreSQL (audit trail, token tracking)
• Cache: Redis (double-spend prevention, hot data)
• Crypto: RSA-3072 blind signatures

Features

• ✅ Token withdrawal (blind signature issuance)
• ✅ Token redemption (verification + double-spend check)
• ✅ Token verification
• ✅ Public key distribution
• ✅ Audit logging
• ✅ Health monitoring

Prerequisites

PostgreSQL Setup

# Install PostgreSQL

sudo apt-get install postgresql postgresql-contrib


# Create database and user

sudo -u postgres psql

CREATE DATABASE ecash_db;
CREATE USER ecash_user WITH PASSWORD 'ecash_password_2024';
GRANT ALL PRIVILEGES ON DATABASE ecash_db TO ecash_user;
\q

# Run schema

psql -U ecash_user -d ecash_db -f schema.sql

Redis Setup

# Install Redis

sudo apt-get install redis-server


# Set password in /etc/redis/redis.conf

requirepass redis_password_2024


# Restart Redis

sudo systemctl restart redis-server

Configuration

Edit .env file:

# Server
SERVER_HOST=0.0.0.0
SERVER_PORT=8080

# PostgreSQL
DATABASE_URL=postgresql://ecash_user:ecash_password_2024@localhost:5432/ecash_db
DATABASE_MAX_CONNECTIONS=10

# Redis
REDIS_URL=redis://:redis_password_2024@localhost:6379
REDIS_MAX_CONNECTIONS=10

# Institution
INSTITUTION_ID=inst_primary
KEY_ID=key_001
TOKEN_EXPIRY_DAYS=90
DENOMINATIONS=10,50,100,500,1000

# Logging
RUST_LOG=info,ecash_server=debug

Build & Run

# Build

cargo build --release


# Run

cargo run --release


# Or run binary

./target/release/ecash-server

API Endpoints

Health Check

GET /health

Get Public Key

GET /api/v1/keys

Withdraw Tokens

POST /api/v1/withdraw

Content-Type: application/json


{
  "amount": 100,

  "denomination": 50,

  "blinded_tokens": [...]

}

Redeem Tokens

POST /api/v1/redeem

Content-Type: application/json


{
  "tokens": [...],

  "merchant_id": "merchant_123"

}

Verify Token

POST /api/v1/verify

Content-Type: application/json


{
  "token": {...}

}

Testing

# Unit tests

cargo test


# Integration tests

cargo test --test '*'


# Health check

curl http://localhost:8080/health


# Get public key

curl http://localhost:8080/api/v1/keys

Performance

Target metrics (single node):

• Withdrawal: <100ms, 100 req/sec
• Redemption: <50ms, 500 req/sec
• Verification: <10ms, 1000 req/sec

Security

• RSA-3072 keys (128-bit security)
• Constant-time signature operations
• Redis-based double-spend prevention
• PostgreSQL audit trail
• Rate limiting (TODO)
• HSM integration (TODO)

Monitoring

Metrics exposed at /metrics (TODO):

• Request latency (p50, p95, p99)
• Request rate
• Error rate
• Database connection pool
• Redis connection pool
• Token issuance/redemption counts

Production Deployment

See deployment/ directory for:

• Docker containers
• Kubernetes manifests
• Nginx reverse proxy config
• Systemd service files

License

See LICENSE file in root directory.