Overview ¶

Contents

Overview
- snarkjs: JavaScript implementation of zkSNARKs.

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.

Tutorial.¶

A good starting point is this tutorial

Also this video is a good starting point.

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");
}

Install.¶

Usage from command line.¶

Usage from javascript¶

License¶