💳 BitSpend

🌟 Introduction

BitSpend is an innovative self-custodial payment card solution that bridges the gap between cryptocurrency and real-world payments. Built on Mezo Testnet, BitSpend enables seamless MUSD token transactions through NFC-enabled cards, combining the security of blockchain technology with the convenience of traditional payment methods. Our project consists of three main components:

1. BitSpend Smart Contracts 🔐: Secure on-chain card management and transaction processing using Shamir Secret Sharing
2. BitSpend Console 🖥️: A user-friendly web interface for card registration, top-ups, and transaction management
3. BitSpend Backend API ⚙️: Secure intermediary server handling card authentication and transaction authorization

At the core of our project is a revolutionary approach to self-custodial payments: customers maintain full control of their funds through split-key cryptography, while merchants enjoy the simplicity of tap-to-pay transactions—no complex wallet interactions required at the point of sale.

🎯 Problem Statement

Cryptocurrency adoption for everyday payments faces significant barriers: customers struggle with complex wallet UIs during transactions, merchants require technical expertise to accept crypto, and existing solutions compromise either security (custodial services) or usability (non-custodial wallets). While physical payment cards offer familiar UX, current crypto card solutions are custodial—users don't truly own their funds. BitSpend solves this through Shamir Secret Sharing, enabling truly self-custodial payment cards that are as easy to use as traditional debit cards, making cryptocurrency payments accessible to everyone without sacrificing security or user control.

🎥 Demo Materials

1. Demo Video 📹
2. Live Demo 🌐
3. Presentation 📊

🏆 Track

• Track: Financial Access & Mass Adoption - For everyday users and underbanked communities

🛠️ Workflow

┌─────────────┐         ┌──────────────┐         ┌─────────────┐
│   Customer  │────────▶│   Merchant   │────────▶│ Blockchain  │
│  (NFC Card) │ Tap Card│  (Phone/POS) │ Submit  │   (Mezo)    │
└─────────────┘         └──────────────┘         └─────────────┘
      │                        │                         │
      │ Share 2 (NFC)          │ Share 1 (Encrypted)     │
      └────────────┬───────────┘                         │
                   │                                     │
                   ▼                                     │
            ┌──────────────┐                             │
            │  Share 3     │◀────────────────────────────┘
            │ (PIN-derived)│    Transaction Confirmed
            └──────────────┘
                   │
                   ▼
            Key Reconstructed
            Transaction Signed

✨ Key Features

🔐 Security First

• Shamir Secret Sharing (SSS): Private key split into 3 shares
  • Share 1: Encrypted and stored in database
  • Share 2: Written to NFC card
  • Share 3: Derived from user's PIN
• Self-Custodial: Users maintain complete control—no third party can access funds
• PIN Protection: Transactions require customer's PIN for authorization
• Daily Spending Limits: Built-in protection against unauthorized use

💳 Seamless User Experience

• Tap to Pay: NFC-enabled cards for contactless payments
• Familiar Flow: Works like traditional debit cards—tap, enter PIN, done
• No Wallet Required: Merchants don't need crypto wallets—just a phone
• Instant Settlement: Transactions confirm in seconds on Mezo Testnet
• Manual Entry Fallback: Works on devices without NFC support

🖥️ BitSpend Console Features

• One-Click Card Registration: Register new payment cards in under 30 seconds
• Easy Top-Ups: Add MUSD tokens to cards instantly
• Dual Payment Modes: NFC scan or manual card entry
• Transaction History: Complete analytics for both merchants and cardholders
• Real-Time Balance Tracking: Monitor card balances and spending limits
• Multi-Wallet Support: MetaMask and WalletConnect integration

⚙️ Smart Contract Architecture

• CardManager Contract: Handles card registration, balance management, and spending limits
• MUSD Token: ERC-20 stablecoin for payments
• On-Chain Verification: All transactions recorded on Mezo blockchain
• Gas Optimization: Efficient contract design for minimal transaction costs
• Daily Limit Enforcement: Automatic reset at midnight UTC

📊 Analytics & Reporting

• Merchant Dashboard: Track sales, revenue, and unique customers
• Card Transaction History: View all payments and top-ups
• Spending Analytics: Monitor daily limits and spending patterns
• Export Capabilities: Download transaction history for accounting

🏗️ Technical Architecture

🔐 Smart Contracts (Solidity)

• CardManager.sol: Core contract managing card lifecycle
  • Card registration with owner verification
  • Balance tracking and transfer logic
  • Daily spending limit enforcement
  • Card activation and deactivation
• MUSD.sol: ERC-20 stablecoin for payments
• Deployed on: Mezo Testnet (Chain ID: 31611)

🖥️ BitSpend Console (React Frontend)

• React 18 with React Router for navigation
• Ethers.js v6 for blockchain interactions
• WalletConnect v2 for mobile wallet support
• TailwindCSS for responsive design
• NFC Web API for contactless card reading
• Hosted on: Vercel

⚙️ BitSpend API (Node.js Backend)

• Express.js REST API
• PostgreSQL database for card data
• Shamir Secret Sharing implementation
• PIN rate limiting and security
• Transaction processing and validation
• Hosted on: Render

🔄 Payment Flow

1. Card Registration

• User connects wallet and registers card
• Smart contract records card address and owner
• Private key split into 3 SSS shares
• Share 2 written to NFC card

2. Top-Up

• User approves MUSD spending
• Transfers tokens to card address
• Balance updated on-chain

3. Payment Processing

• Customer taps NFC card on merchant's phone
• Merchant enters payment amount
• Customer enters PIN on merchant's device
• Backend reconstructs private key from 3 shares
• Transaction signed and submitted to blockchain
• Confirmation returned to both parties

🔒 Security Features

• End-to-End Encryption: Sensitive data encrypted in transit and at rest
• No Single Point of Failure: Key cannot be reconstructed without all 3 shares
• PIN Rate Limiting: Protection against brute force attacks
• Transaction Verification: All payments validated on-chain
• Audit Trail: Complete transaction history on blockchain

🚀 Innovation Highlights

💡 Unique Value Propositions

1. True Self-Custody: First payment card solution that's genuinely non-custodial
2. Zero Learning Curve: Familiar payment UX—no crypto knowledge required
3. Merchant-Friendly: Accept crypto payments with just a smartphone
4. Blockchain Transparency: All transactions verifiable on-chain
5. Flexible Entry: Works with or without NFC support

🎯 Target Use Cases

• Retail Payments: Coffee shops, restaurants, convenience stores
• Peer-to-Peer Payments: Send money between friends
• Micro-Transactions: Small purchases under daily limits
• Remittances: Cross-border payments with instant settlement
• Event Payments: Festivals, conferences, farmers markets

📈 Future Roadmap

Phase 1 (Current - MVP) ✅

• ✅ Card registration and management
• ✅ NFC tap-to-pay functionality
• ✅ Manual entry fallback
• ✅ Basic transaction history
• ✅ MetaMask & WalletConnect integration

Phase 2 (Next 3 Months)

• Multi-currency support (ETH, USDC, DAI)
• Mobile app (iOS & Android)
• QR code payment option
• Advanced analytics dashboard
• Merchant API for POS integration

Phase 3 (6+ Months)

• Physical card manufacturing partnership
• Multi-chain support (Ethereum, Polygon, etc.)
• Recurring payment subscriptions
• Loyalty rewards program
• Integration with existing POS systems

Phase 4 (Future Vision)

• Decentralized card issuance network
• Zero-knowledge proof authentication
• Hardware wallet integration
• SDK for third-party integrations
• Governance token for ecosystem participants

👥 Team Information

Jay Shitre 🎨

• Role: Full-Stack Developer
• Expertise: React, Solidity, Node.js, Blockchain Integration
• Responsibilities: Frontend development, smart contract development, backend API

Nidhi Tikone 🎨

• Role: Full-Stack Developer
• Expertise: React, Node.js, UX Design, Blockchain Integration
• Responsibilities: Frontend development, backend API

🔗 Links & Resources

• Live Demo: bitspend.app
• GitHub Repository: github.com/your-repo
• Smart Contracts: Mezo Explorer
• Documentation: GitBook/Docs
• Demo Video: YouTube

🎓 Technical Stack

Frontend

• React 18
• React Router
• TailwindCSS
• Ethers.js v6
• WalletConnect v2
• Web NFC API

Backend

• Node.js
• Express.js
• PostgreSQL
• Shamir Secret Sharing library

Blockchain

• Solidity 0.8.x
• Hardhat development environment
• Mezo Testnet (EVM-compatible)

DevOps

• Vercel (Frontend)
• Render (Backend)
• GitHub Actions (CI/CD)
• PostgreSQL (Managed Database)

📦 Repository Structure

bitspend/
├── frontend/           # React web application
├── backend/            # Node.js API server
├── contracts/          # Solidity smart contracts
└── README.md          # This file

🚀 Quick Start

Prerequisites

• Node.js v18+
• PostgreSQL
• MetaMask wallet
• Git

Installation

# Clone the repository
git clone https://github.com/your-username/bitspend.git
cd bitspend

# Install frontend dependencies
cd frontend
npm install

# Install backend dependencies
cd ../backend
npm install

# Install contract dependencies
cd ../contracts
npm install

Environment Setup

Frontend (.env)

REACT_APP_API_URL=http://localhost:5000
REACT_APP_CARD_MANAGER_ADDRESS=0x...
REACT_APP_MUSD_ADDRESS=0x...
REACT_APP_WALLETCONNECT_PROJECT_ID=your_project_id

Backend (.env)

PORT=5000
DATABASE_URL=postgresql://...
JWT_SECRET=your_secret
ENCRYPTION_KEY=your_encryption_key
MEZO_RPC_URL=https://rpc.test.mezo.org
CARD_MANAGER_ADDRESS=0x...

Running Locally

# Terminal 1 - Start backend
cd backend
npm run dev

# Terminal 2 - Start frontend
cd frontend
npm start

# Terminal 3 - Deploy contracts (if needed)
cd contracts
npx hardhat run scripts/deploy.js --network mezo-testnet

🧪 Testing

# Run frontend tests
cd frontend
npm test

# Run backend tests
cd backend
npm test

# Run contract tests
cd contracts
npx hardhat test

🙏 Acknowledgments

We're excited to present BitSpend and demonstrate how it can revolutionize everyday cryptocurrency payments. Our solution combines the security of self-custodial wallets with the simplicity of traditional payment cards, making blockchain technology accessible for real-world transactions. BitSpend proves that crypto payments can be both secure and user-friendly—no compromises necessary.

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Built with ❤️ for the future of payments

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🌟 Star Us!

If you find BitSpend interesting, please consider giving us a star ⭐ on GitHub!