Hardhat ZKit

The ultimate TypeScript environment for Circom development.

What

This hardhat plugin is a zero-config, one-stop Circom development environment that streamlines circuits management and lets you focus on the important - code.

• Developer-oriented abstractions that simplify r1cs, witness, zkey, and vkey generation processes.
• Support of groth16 and plonk proving systems.
• Recompilation and resetup 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.
• Practical witness and proof testing via chai assertions.
• Invisible platform-specific and wasm-based Circom compiler management.
• Simplified node_modules libraries resolution.
• Rich plugin configuration.
• And much more!

Installation

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

And add the following line to your hardhat.config:

import "@solarity/hardhat-zkit"; // TypeScript

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

Tip

There is no need to download the Circom compiler separately. The plugin automatically installs required compilers 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: {
    compilerVersion: "2.1.9",
    circuitsDir: "circuits",
    compilationSettings: {
      artifactsDir: "zkit/artifacts",
      onlyFiles: [],
      skipFiles: [],
      c: false,
      json: false,
      optimization: "O1",
    },
    setupSettings: {
      contributionSettings: {
        provingSystem: "groth16", // or "plonk"
        contributions: 2,
      },
      onlyFiles: [],
      skipFiles: [],
      ptauDir: undefined,
      ptauDownload: true,
    },
    verifiersSettings: {
      verifiersDir: "contracts/verifiers",
      verifiersType: "sol", // or "vy"
    },
    typesDir: "generated-types/zkit",
    quiet: false,
  },
};

Where:

• compilerVersion - The value to indicate which Circom compiler to use (latest by default).
• 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.
  • optimization - The flag to set the level of constraint simplification during compilation ("O0", "O1" or "O2").
• setupSettings
  • contributionSettings
    • provingSystem - The option to indicate which proving system to use ("groth16", "plonk" or ["groth16", "plonk"]).
    • 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.
• verifiersSettings
  • verifiersDir - The directory where to generate the Solidity | Vyper verifiers.
  • verifiersType - The option ("sol" or "vy") to indicate which language to use for verifiers generation.
• typesDir - The directory where to save the generated typed circuits wrappers.
• quiet - The flag indicating whether to suppress the output.

Tasks

There are several hardhat tasks in the zkit scope that the plugin provides:

• compile task that compiles or recompiles the modified circuits with the main component.
• setup task that generates or regenerates zkey and vkey for the previously compiled circuits.
• make task that executes both compile and setup for convenience.
• verifiers task that generates Solidity | Vyper verifiers for all the previously setup circuits.
• clean task that cleans up the generated artifacts, types, etc.

To view the available options, run the help command:

npx hardhat help zkit <zkit task name>

Typization

The plugin provides full TypeScript typization of Circom circuits leveraging zktype library. Both groth16 and plonk proving systems are supported.

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

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

Testing

In order to utilize user-friendly Chai assertions for witness and ZK proof testing, the chai-zkit package needs to be installed:

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

And add the following line to your hardhat.config:

import "@solarity/chai-zkit"; // TypeScript

require("@solarity/chai-zkit"); // JavaScript

The package extends expect chai assertion to recognize typed zktype objects for frictionless testing experience.

Note

Please note that for witness testing purposes it is sufficient to compile circuits just with zkit compile task, without generating the keys.

Example

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; } // main component to compile the circuit component main = Multiplier();

// file location: ./test/multiplier.test.ts import { zkit } from "hardhat"; // hardhat-zkit plugin import { expect } from "chai"; // chai-zkit extension import { Multiplier } from "@zkit"; // zktype circuit-object describe("Multiplier", () => { it("should test the circuit", async () => { const circuit: Multiplier = await zkit.getCircuit("Multiplier"); // or await zkit.getCircuit("circuits/multiplier.circom:Multiplier"); // witness testing await expect(circuit) .with.witnessInputs({ in1: "3", in2: "7" }) .to.have.witnessOutputs({ out: "21" }); // proof testing const proof = await circuit.generateProof({ in1: "4", in2: "2" }); await expect(circuit).to.verifyProof(proof); }); });

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

npx hardhat zkit make

This command will install the newest compatible Circom compiler, compile the provided circuit, download the necessary ptau file regarding the number of circuit's constraints and the proving system of choice, build the required zkey and vkey files, and generate TypeScript object wrappers to enable full typization of signals and ZK proofs.

Afterward, copy the provided script to the test directory and run the tests via npx hardhat test. You will see that all the tests are passing!

Check out the Medium blog post to learn more.

API reference

---

• async getCircuit(<circuitName|fullCircuitName>, <provingSystem?>) -> zkit

The method accepts the name of the main component of the circuit, optional proving system 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.

The optional provingSystem parameter should only be specified if multiple proving systems were set in the config. Otherwise, leave it as undefined.

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 there is minimal support for var Circom variables. Some circuits may not work if you are using complex var-dependent expressions.
• Even though the plugin provides support of Circom v2.2.0, its newest feature bus is not supported.
• Due to current wasm memory limitations (address space is 32-bit), the plugin may fail to compile especially large circuits on some platforms.