snarkjs

snarkjs: JavaScript implementation of zkSNARKs.

This is a JavaScript implementation of zkSNARK schemes. It allows the original 8points protocol and the Groth Protocol (3 point only and 3 pairings)

This library allows to do the trusted setup, generate proofs and verify the proofs.

This library uses the compiled circuits generated by the jaz compiler.

Install.

npm install snarkjs

Usage from command line.

snarkjs --help

Will show all the info in how to use the cli.

Usage from javascript

Import.

const zkSnark = require("snarkjs");

Load a circuit.

// "myCircuit.cir" is the output of the jaz compiler

const circuitDef = JSON.parse(fs.readFileSync("myCircuit.cir", "utf8"));
const circuit = new zkSnark.Circuit(circuitDef);

Inspect the circuit.

    // `signalId` can always be a number or an alias string

    circuit.nConstraints; // number of constraints
    circuit.nSignals; // number of signals
    circuit.nPublic; // number of public signals (nOutputs + nPublicInputs)

    // The array of signals is always sorted in this order:
    // [ 1, outputs, publicInputs, privateInputs, internalSignals, constants]

    // returns a,b and c coeficients of the `signalId` on a given `constraint`
    circuit.a(constraint, signalId)
    circuit.b(constraint, signalId)
    circuit.c(constraint, signalId)

    circuit.nOutputs           // number of public outputs
    circuit.pubInputs          // number of public inputs
    circuit.nPrvInputs         // number of private inputs
    circuit.nInputs            // number of inputs ( nPublicInputs + nPrivateInputs)
    circuit.nVars              // number of variables ( not including constants (one is a variable) )
    circuit.nSignals           // number of signals ( including constants )

    circuit.outputIdx(i)       // returns the index of the i'th output
    circuit.inputIdx(i)        // returns the index of the i'th input
    circuit.pubInputIdx(i)     // returns the index of the i'th public input
    circuit.prvInputIdx(i)     // returns the index of the i'th private input
    circuit.varIdx(i)          // returns the index of the i'th variable
    circuit.constantIdx(i)     // returns the index of the i'th constant
    circuit.signalIdx(i)       // returns the index of the i'th signal

    // returns signal Idx given a signalId
    // if the idx >= n , it is a constant
    // if the idx == -1, the signal does not exist
    circuit.getSignalIdx(name);

    // returns an array aliases names of the i'th signal
    circuit.signalNames(i)

    // input is a key value object where keys are the signal names
    //   of all the inputs (public and private)
    // returns an array of values representing the witness
    circuit.calculateWitness(input)

Trusted setup.

const setup = zkSnark.setup(circuit);
fs.writeFileSync("myCircuit.vk_proof", JSON.stringify(setup.vk_proof), "utf8");
fs.writeFileSync("myCircuit.vk_verifier", JSON.stringify(setup.vk_verifier), "utf8");
setup.toxic  // Must be discarded.

Generate proof.

const circuitDef = JSON.parse(fs.readFileSync("myCircuit.cir", "utf8"));
const circuit = new zkSnark.Circuit(circuitDef);
const input = {
    "main.pubIn1": "123",
    "main.out1": "456"
}
const witness = circuit.calculateWitness(input);
const vk_proof = JSON.parse(fs.readFileSync("myCircuit.vk_proof", "utf8"));

const {proof, publicSignals} = zkSnark.genProof(vk_proof, witness);

Verifier.

const vk_verifier = JSON.parse(fs.readFileSync("myCircuit.vk_verifier", "utf8"));

if (zkSnark.isValid(vk_verifier, proof, publicSignals)) {
    console.log("The proof is valid");
} else {
    console.log("The proof is not valid");
}

License

snarkjs is part of the iden3 project copyright 2018 0KIMS association and published with GPL-3 license. Please check the COPYING file for more details.