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 lets you focus on the important - code.

• Developer-oriented abstractions that simplify r1cs, zkey, vkey, and witness generation processes.
• Recompilation of only the modified circuits.
• Full TypeScript typization of signals and ZK proofs.
• Automatic downloads of phase-1 ptau files.
• Convenient phase-2 contributions to zkey files.
• Invisible wasm-based Circom compiler management.
• Simplified node_modules libraries resolution.
• 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,
    },
    typesSettings: {
      typesArtifactsDir: "zkit/abi",
      typesDir: "generated-types/zkit",
    },
    verifiersDir: "contracts/verifiers",
    ptauDir: undefined,
    ptauDownload: true,
    nativeCompiler: false,
    quiet: false,
  },
};

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.
• typesSettings
  • typesArtifactsDir - The directory where to save the generated circuits ABI.
  • typesDir - The directory where to save the generated circuits wrappers.
• 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 download of required ptau files.
• nativeCompiler - The flag indicating whether to use the natively installed compiler.
• quiet - The flag indicating whether to suppress the output.

Important

The nativeCompiler flag requires the Circom compiler to be preinstalled and be globally available in the system.

Typization

The plugin provides full TypeScript typization of Circom circuits leveraging zktype library.

The following config may be added to tsconfig.json file to allow for a better user experience:

{
  "compilerOptions": {
    "paths": {
      "@zkit": ["./generated-types/zkit"]
    }
  }
}

Tasks

There are several hardhat tasks that the plugin provides:

• zkit:compile task that compiles or recompiles the modified circuits with the main component.
• zkit:verifiers task that generates Solidity verifiers for all the previously compiled 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 typed circuits to be used in scripts and tests:

Circom circuit

Usage example

// file location: ./circuits/multiplier.circom 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"; import { Multiplier } from "@zkit"; // typed circuit-object async function main() { const circuit: Multiplier = await zkit.getCircuit("Multiplier"); // OR await zkit.getCircuit("circuits/multiplier.circom:Multiplier"); const proof = await circuit.generateProof({ in1: "4", in2: "2" }); await circuit.verifyProof(proof); // success } main() .then() .catch((e) => console.log(e));

API reference

---

• getCircuit(<fullCircuitName|circuitName>) -> zkit

The method accepts the name of the main component of the circuit and returns the instantiated zkit object pointing to that circuit.

Note

Please note that the zktype typed wrapper object gets actually returned which enables full TypeScript typization.

In case there are conflicts between circuit file names and main component names, you should use the fullCircuitName, which has the following form: circuitSourceName:circuitName.

Where:

• circuitSourceName - Path to the circuit file from the project root.
• circuitName - Circuit main component name.

Important

Check out the zkit documentation to understand zkit objects capabilities.

Known limitations

• Currently the Circom 2.1.8 is used to compile circuits.
• Temporarily, the only supported proving system is groth16.