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ZKard: Rechargeable Anonymous Payment System

ZKard is an innovative payment system built on zkSync, enabling fast, permissionless, and anonymous payments. This monorepo contains both the card emissor and the frontend code for the checkout process.

graph TD
    A[Start: NFC Card Scanned] --> B{Check Operation Type}
    B -->|Pay| C[Validate Associated Account Balance]
    B -->|Recharge| H[Get Recharge Amount]
    
    C -->|Valid Balance| D[Process Payment]
    C -->|Insufficient Balance| E[Display Error: Insufficient Funds]
    
    D --> F[Update Account Balance]
    F --> G[Complete Transaction]
    
    H --> I[Send Funds to Associated Wallet]
    I --> J[Update Account Balance]
    J --> K[Complete Recharge]
    
    E --> L[End: Transaction Failed]
    G --> M[End: Payment Successful]
    K --> N[End: Recharge Successful]
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Project Overview

ZKard leverages blockchain technology to provide a seamless and secure payment experience:

  • Each ntag424 card is uncloneable and its signature can be verified by the emissor.
  • Cards are associated with Abstract Accounts that can be "recharged".
  • The emissor owns these accounts and can make payments from them when verified by the card signature.
  • Gas fees are handled by a General Paymaster that maintains a list of addresses it pays for (the addresses associated with the cards).

The result is a transparent experience for the end user: Tap to pay, fast and secure.

screenshot

screenshot

Monorepo Structure

This project uses Turborepo to manage the monorepo structure. The main packages are:

  • apps/card: Card emissor functionality
  • apps/checkout: Frontend code for the checkout process

Contract

Prerequisites

  • Node.js (v14 or later)
  • pnpm (v6 or later)
  • MetaMask or another Ethereum wallet

Installation

  1. Clone the repository:

    git clone https://github.com/your-username/zkard.git
cd zkard

  2. Install dependencies:

    pnpm install

  3. Create a .env file in the root directory and add your environment variables:

    NEXT_PUBLIC_DEFAULT_CHAIN=zkSync_era

Running the Applications

To start all applications in development mode:

pnpm run dev

To run a specific app:

pnpm run dev --filter=emissor
# or
pnpm run dev --filter=checkout

The apps will be available at:

Building the Project

To build all packages and apps:

pnpm run build

Features

  • Rechargeable ZKard system
  • Card emissor functionality
  • Checkout frontend
  • Integration with zkSync and ethers.js
  • Next.js-based web applications
  • Wallet connection (MetaMask, etc.)
  • Network switching (zkSync Era, zkSync Sepolia Testnet, zkSync Goerli Testnet)
  • Account information and balance display
  • Smart contract interactions (read/write)
  • Transaction sending
  • Message and typed data signing
  • Contract event and pending transaction monitoring
  • ERC20 token interactions

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License.

Acknowledgements