Hardhat ZKit

The ultimate environment for building with Circom.

What

This hardhat plugin is a zero-config, one-stop Circom development environment that abstracts away circuits management hassle and let's you focus on the important - code.

• Developer-oriented abstractions that simplify r1cs, zkey, vkey, and witness generation processes.
• Recompilation of only the modified circuits.
• Automatic downloads of phase-1 ptau files.
• Quick phase-2 contributions to zkey files.
• Invisible wasm-based Circom compiler management.
• Zero platform-specific dependencies: everything is in TypeScript.
• Extensive development and testing API.
• Rich plugin configuration.
• And much more!

Installation

npm install --save-dev @solarity/hardhat-zkit

And add the following line to your hardhat.config:

require("@solarity/hardhat-zkit");

Or if you are using TypeScript:

import "@solarity/hardhat-zkit";

Tip

There is no need to download the Circom compiler separately. The plugin works with the WASM-based version under the hood.

Usage

The hardhat-zkit is a zero-config plugin, however you may add the following to your hardhat.config file:

module.exports = {
  zkit: {
    circuitsDir: "circuits",
    compilationSettings: {
      artifactsDir: "zkit/artifacts",
      onlyFiles: [],
      skipFiles: [],
      c: false,
      json: false,
      sym: false,
      contributionTemplate: "groth16",
      contributions: 1,
    },
    quiet: false,
    verifiersDir: "contracts/verifiers",
    ptauDir: undefined,
    ptauDownload: true,
  },
};

Where:

• circuitsDir - The directory where to look for the circuits.
• compilationSettings
  • artifactsDir - The directory where to save the circuits artifacts (r1cs, zkey, etc).
  • onlyFiles - The list of directories (or files) to be considered for the compilation.
  • skipFiles - The list of directories (or files) to be skipped for the compilation.
  • c - The flag to generate the c-based witness generator (generates wasm by default).
  • json - The flag to output the constraints in json format.
  • sym - The flag to output the constraint system in an annotated mode.
  • contributionTemplate - The option to indicate which proving system to use.
  • contributions - The number of phase-2 zkey contributions to make if groth16 is chosen.
• quiet - The flag indicating whether to suppress the output.
• verifiersDir - The directory where to generate the Solidity verifiers.
• ptauDir - The directory where to look for the ptau files. $HOME/.zkit/ptau/ by default.
• ptauDownload - The flag to allow automatic dowload of required ptau files.

Tasks

There are several hardhat tasks that the plugin provides:

• zkit:compile task that compiles or recompiles the modified circuits that have the main component.
• zkit:verifiers task that generates Solidity verifiers for all the available circuits.

To view the available options, run the help command:

npx hardhat help zkit:compile
npx hardhat help zkit:verifiers

Environment extensions

The plugin extends the hardhat environment with the zkit object that allows circuits to be used in scripts and tests:

Circom circuit	Usage example
pragma circom 2.0.0; template Multiplier(){ signal input in1; signal input in2; signal output out; out <== in1 * in2; } component main = Multiplier();	import { zkit } from "hardhat"; async function main() { const circuit = await zkit.getCircuit("multiplier"); // "multiplier" is the file name const proof = await circuit.generateProof({ in1: "4", in2: "2" }); await circuit.verifyProof(proof); // success await circuit.createVerifier(); } main() .then() .catch((e) => console.log(e));

API reference

---

• getCircuit(<filename>) -> zkit

The method accepts the filename of the circuit where its main component is defined. Returns the instanciated zkit object.

Important

Check out the zkit documentation to understand zkit objects capabilities.

Known limitations

• Currently the Circom 2.1.8 is used for the compilation of circuits.
• Temporarily, the only supported proving system is groth16.
• Full TypeScript typization of circuits is in progress.