snarkjs/src/groth16_verify.js

zkSNARKs implementation in JavaScript

/*
    Copyright 2018 0kims association.

    This file is part of snarkjs.

    snarkjs is a free software: you can redistribute it and/or
    modify it under the terms of the GNU General Public License as published by the
    Free Software Foundation, either version 3 of the License, or (at your option)
    any later version.

    snarkjs is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
    more details.

    You should have received a copy of the GNU General Public License along with
    snarkjs. If not, see <https://www.gnu.org/licenses/>.
*/

/* Implementation of this paper: https://eprint.iacr.org/2016/260.pdf */
import { Scalar } from "ffjavascript";
import * as curves from "./curves.js";
import {  utils }   from "ffjavascript";
const {unstringifyBigInts} = utils;

export default async function groth16Verify(_vk_verifier, _publicSignals, _proof, logger) {
/*
    let cpub = vk_verifier.IC[0];
    for (let s= 0; s< vk_verifier.nPublic; s++) {
        cpub  = G1.add( cpub, G1.timesScalar( vk_verifier.IC[s+1], publicSignals[s]));
    }
*/

    const vk_verifier = unstringifyBigInts(_vk_verifier);
    const proof = unstringifyBigInts(_proof);
    const publicSignals = unstringifyBigInts(_publicSignals);

    const curve = await curves.getCurveFromName(vk_verifier.curve);

    const IC0 = curve.G1.fromObject(vk_verifier.IC[0]);
    const IC = new Uint8Array(curve.G1.F.n8*2 * publicSignals.length);
    const w = new Uint8Array(curve.Fr.n8 * publicSignals.length);

    if (!publicInputsAreValid(curve, publicSignals)) {
        if (logger) logger.error("Public inputs are not valid.");
        return false;
    }

    for (let i=0; i<publicSignals.length; i++) {
        const buffP = curve.G1.fromObject(vk_verifier.IC[i+1]);
        IC.set(buffP, i*curve.G1.F.n8*2);
        Scalar.toRprLE(w, curve.Fr.n8*i, publicSignals[i], curve.Fr.n8);
    }

    let cpub = await curve.G1.multiExpAffine(IC, w);
    cpub = curve.G1.add(cpub, IC0);

    const pi_a = curve.G1.fromObject(proof.pi_a);
    const pi_b = curve.G2.fromObject(proof.pi_b);
    const pi_c = curve.G1.fromObject(proof.pi_c);

    if (!isWellConstructed(curve, {pi_a, pi_b, pi_c})) {
        if(logger) logger.error("Proof commitments are not valid.");
        return false;
    }

    const vk_gamma_2 = curve.G2.fromObject(vk_verifier.vk_gamma_2);
    const vk_delta_2 = curve.G2.fromObject(vk_verifier.vk_delta_2);
    const vk_alpha_1 = curve.G1.fromObject(vk_verifier.vk_alpha_1);
    const vk_beta_2 = curve.G2.fromObject(vk_verifier.vk_beta_2);

    const res = await curve.pairingEq(
        curve.G1.neg(pi_a) , pi_b,
        cpub , vk_gamma_2,
        pi_c , vk_delta_2,

        vk_alpha_1, vk_beta_2
    );

    if (! res) {
        if (logger) logger.error("Invalid proof");
        return false;
    }

    if (logger) logger.info("OK!");
    return true;
}

function isWellConstructed(curve, proof) {
    const G1 = curve.G1;
    const G2 = curve.G2;

    return G1.isValid(proof.pi_a)
        && G2.isValid(proof.pi_b)
        && G1.isValid(proof.pi_c);
}

function publicInputsAreValid(curve, publicInputs) {
    for(let i = 0; i < publicInputs.length; i++) {
        if(!Scalar.lt(publicInputs[i], curve.r)) {
            return false;
        }
    }
    return true;
}