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,
    },
    setupSettings: {
      contributionSettings: {
        contributionTemplate: "groth16",
        contributions: 1,
      },
      onlyFiles: [],
      skipFiles: [],
      ptauDir: undefined,
      ptauDownload: true,
    },
    typesSettings: {
      typesArtifactsDir: "zkit/abi",
      typesDir: "generated-types/zkit",
    },
    verifiersDir: "contracts/verifiers",
    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 excluded from 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.
• setupSettings
  • contributionSettings
    • contributionTemplate - The option to indicate which proving system to use.
    • contributions - The number of phase-2 zkey contributions to make if groth16 is chosen.
  • onlyFiles - The list of directories (or files) to be considered for the setup phase.
  • skipFiles - The list of directories (or files) to be excluded from the setup phase.
  • 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.
• typesSettings
  • typesArtifactsDir - The directory where to save the generated circuits ABI.
  • typesDir - The directory where to save the generated typed circuits wrappers.
• verifiersDir - The directory where to generate the Solidity verifiers.
• nativeCompiler - The flag indicating whether to use the natively installed compiler.
• quiet - The flag indicating whether to suppress the output.

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:setup task that generates or regenerates zkey and vkey for the previously compiled circuits.
• zkit:make task that executes both zkit:compile and zkit:setup for convenience.
• zkit:verifiers task that generates Solidity verifiers for all the previously setup circuits.
• zkit:clean task that cleans up the generated artifacts, types, etc.

To view the available options, run the help command:

npx hardhat help <zkit task name>

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));

To see the plugin in action, place the Multiplier circuit in the circuits directory and execute:

npx hardhat zkit:make

This command will compile the circuit leveraging wasm-based Circom compiler, download the necessary ptau file regarding the number of constraints, build the required zkey and vkey files, and generate TypeScript object wrappers to enable full typization of signals and ZK proofs.

Afterward, you may proceed with the provided hardhat script.

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.

The method works regardless of how the circuit was compiled, however, if zkit:compile task was used, the zkit methods that utilize proof generation or proof verification would throw an error by design.

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

Please note that the method actually returns the zktype typed zkit wrapper objects which enable full TypeScript typization of signals and proofs. Also, check out the zkit documentation to understand zkit object capabilities and how to interact with circuits.

Known limitations

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