koalateectrl / zk-example

Example for how to use Circom + Solidity for on-chain ZK verification

ZK Example using Circom and Solidity with Hardhat

A basic circom project using Hardhat, hardhat-circom, and snark-js.

Install

yarn to install dependencies

Build

yarn circom:dev to build deterministic development circuits.

Further, for debugging purposes, you may wish to inspect the intermediate files. This is possible with the --debug flag which the circom:dev task enables by default. You'll find them (by default) in artifacts/circom/

To ensure that the proof is generated correctly, you can verify it with yarn dev:verify-proof.

Tests can be run using yarn test. As convention in Hardhat, the tests will be located in the test folder.

Deployment

To deploy to Sepolia network using Infura, first create .env file following the example in .env.example and fill in the two fields.

Then, run npx hardhat run scripts/deploy.js --network sepolia to deploy the ZK.sol contract. This will compile the contract and deploy it to the Goerli network. To verify the contract, run npx hardhat verify --network sepolia <address>.

Generate Solidity Calldata

To interact with the deployed contract, we need to generate the appropriate calldata to pass into Solidity. To do this, we will perform the steps below.

1. yarn circom:prod
2. yarn witness-calc
3. yarn create-proof
4. yarn verify-proof
5. yarn generate-call

The output of the last command will be the calldata needed for Solidity. I have written a file called hexConverter.js that takes the snarkjs output and returns in into a format suitable to use as parameters into a smart contract. Note that if you don't want to use this hexConverter.js file and run the raw snarkjs command, then the value of b is a 2 x 2 array and will need to be split up into two inputs of 1 x 2 arrays for function arguments. Also, note that all values generated are in hex and may need to be converted into decimal before inputing as function arguments.

Acknowledgements

Circuit Circom code taken from 0xPARC