zkVerify EVM DApp Example

This repository provides a simple example of a decentralized application (DApp) that leverages zkVerify for off-chain proof verification, via zkVerifyJS. The DApp demonstrates how to integrate a zk-SNARK circuit, deploy Solidity smart contracts that interact with zkVerify's attestation contract, and build a user interface to interact with the system.

Folder Structure

The repository is organized into three main directories:

• app: Contains the frontend of the DApp, built with Node.js. This is the user-facing part of the application.
• circuit: Contains the zk-SNARK circuit written in Circom. This is where the logic for the zero-knowledge proof is defined.
• contracts: Contains the Solidity smart contracts, managed with Foundry. These contracts are deployed to an Ethereum-compatible blockchain and interact with the zkVerify attestation contract.

Prerequisites

Before you begin, ensure you have the following installed:

• Node.js
• Foundry
• Circom
• snarkjs

Installation and Setup

1. Clone the repository:

   git clone https://github.com/zkVerify/zkverify-evm-dapp-example.git
   cd zkverify-evm-dapp-example

2. Install Node.js dependencies:

   cd app
   npm install
   cd ..

3. Set up environment variables:

   In the app and contracts directories, you will find .env.template and .env.secrets.template files. Copy these to .env and .env.secrets respectively:

   cp app/.env.template app/.env
   cp contracts/.env.template contracts/.env

   Fill in the required values, such as your private key and RPC URL.

Development and Deployment Workflow

1. Circuit Development

The circuit directory contains the Circom code for the zk-SNARK. The Makefile in this directory automates the process of compiling the circuit and generating the necessary keys.

• Compile the circuit and generate keys:

  cd circuit
  make

  This command will:

  1. Compile the circuit.circom file.
  2. Perform a local trusted setup (for demonstration purposes, do not use in production).
  3. Generate the proving key (circuit_final.zkey), verification key (verification_key.json), and a WebAssembly version of the circuit (circuit.wasm).
  4. Place the generated files in the setup directory.

2. Smart Contract Development

The contracts directory contains the Solidity smart contracts, managed with Foundry.

• Build the contracts:

  cd contracts
  forge build

• Deploy the contracts:

  The deployment scripts are located in the script directory. To deploy the contracts, first copy the .env.template file to .env:

  cd contracts
  forge script script/ZkFactorization.s.sol:ZkFactorizationContractScript --rpc-url <your_rpc_url> --private-key <your_private_key>

3. DApp Interaction

The app directory contains the Node.js application that serves as the frontend for the DApp. zkVerifyJS is used to interact with the zkVerify Blockchain.

• Run the DApp:

  cd app
  node index.js

End-to-End User Workflow

1. Generate a Proof: The user interacts with the DApp's frontend. The DApp uses the compiled circuit (circuit.wasm) and the proving key (circuit_final.zkey) to generate a proof based on the user's input.

2. Submit Proof to zkVerify: The DApp sends the generated proof and public inputs to the zkVerify service for verification.

3. Receive Proof ID: zkVerify verifies the proof and, if valid, returns a unique proofId.

4. Interact with the Smart Contract: The DApp calls a function on the deployed smart contract, passing the proofId as an argument.

5. On-Chain Attestation: The smart contract communicates with the zkVerify attestation contract, providing the proofId. The attestation contract checks if a proof with that ID has been successfully verified by zkVerify.

6. Execute Logic: If the proof is valid, the smart contract proceeds with its logic (e.g., minting an NFT, transferring tokens, etc.).

Next Steps

Check out zkVerify documentation for additional info and tutorials:

• zkVerify Contracts
• zkVerify Supported Verifiers
• zkVerifyJS
• Dapp Developer Tutorial
• Utility Solidity Library for DApp Developers
• zkVerify Aggregation Contract