snarkjs/src/zkey_bellman_contribute.js

// Format of the output
//      Hash of the last contribution  64 Bytes
//      2^N*2-1 TauG1 Points (compressed)
//      2^N TauG2 Points (compressed)
//      2^N AlphaTauG1 Points (compressed)
//      2^N BetaTauG1 Points (compressed)
//      Public Key
//          BetaG2 (compressed)
//          G1*s (compressed)
//          G1*s*tau (compressed)
//          G1*t (compressed)
//          G1*t*alpha (compressed)
//          G1*u (compressed)
//          G1*u*beta (compressed)
//          G2*sp*tau (compressed)
//          G2*tp*alpha (compressed)
//          G2*up*beta (compressed)

import * as fastFile from "fastfile";
import Blake2b from "blake2b-wasm";
import * as utils from "./zkey_utils.js";
import * as misc from "./misc.js";
import { applyKeyToChallangeSection } from "./mpc_applykey.js";
import { hashPubKey } from "./zkey_utils.js";
import { hashToG2 as hashToG2 } from "./keypair.js";

export default async function bellmanContribute(curve, challangeFilename, responesFileName, entropy, logger) {
    await Blake2b.ready();

    const rng = await misc.getRandomRng(entropy);

    const delta = curve.Fr.fromRng(rng);
    const invDelta = curve.Fr.inv(delta);

    const sG1 = curve.G1.F.n8*2;
    const sG2 = curve.G2.F.n8*2;

    const fdFrom = await fastFile.readExisting(challangeFilename);
    const fdTo = await fastFile.createOverride(responesFileName);


    await copy(sG1); // alpha1
    await copy(sG1); // beta1
    await copy(sG2); // beta2
    await copy(sG2); // gamma2
    const oldDelta1 = await readG1();
    const delta1 = curve.G1.timesFr(oldDelta1, delta);
    await writeG1(delta1);
    const oldDelta2 = await readG2();
    const delta2 = curve.G2.timesFr(oldDelta2, delta);
    await writeG2(delta2);

    // IC
    const nIC = await fdFrom.readUBE32();
    await fdTo.writeUBE32(nIC);
    await copy(nIC*sG1);

    // H
    const nH = await fdFrom.readUBE32();
    await fdTo.writeUBE32(nH);
    await applyKeyToChallangeSection(fdFrom, fdTo, null, curve, "G1", nH, invDelta, curve.Fr.e(1), "UNCOMPRESSED", "H", logger);

    // L
    const nL = await fdFrom.readUBE32();
    await fdTo.writeUBE32(nL);
    await applyKeyToChallangeSection(fdFrom, fdTo, null, curve, "G1", nL, invDelta, curve.Fr.e(1), "UNCOMPRESSED", "L", logger);

    // A
    const nA = await fdFrom.readUBE32();
    await fdTo.writeUBE32(nA);
    await copy(nA*sG1);

    // B1
    const nB1 = await fdFrom.readUBE32();
    await fdTo.writeUBE32(nB1);
    await copy(nB1*sG1);

    // B2
    const nB2 = await fdFrom.readUBE32();
    await fdTo.writeUBE32(nB2);
    await copy(nB2*sG2);


    //////////
    /// Read contributions
    //////////
    const transcriptHasher = Blake2b(64);

    const mpcParams = {};
    // csHash
    mpcParams.csHash =  await fdFrom.read(64);
    transcriptHasher.update(mpcParams.csHash);

    const nConttributions = await fdFrom.readUBE32();
    mpcParams.contributions = [];
    for (let i=0; i<nConttributions; i++) {
        const c = { delta:{} };
        c.deltaAfter = await readG1();
        c.delta.g1_s = await readG1();
        c.delta.g1_sx = await readG1();
        c.delta.g2_spx = await readG2();
        c.transcript = await fdFrom.read(64);
        mpcParams.contributions.push(c);
        hashPubKey(transcriptHasher, curve, c);
    }

    const curContribution = {};
    curContribution.delta = {};
    curContribution.delta.prvKey = delta;
    curContribution.delta.g1_s = curve.G1.toAffine(curve.G1.fromRng(rng));
    curContribution.delta.g1_sx = curve.G1.toAffine(curve.G1.timesFr(curContribution.delta.g1_s, delta));
    utils.hashG1(transcriptHasher, curve, curContribution.delta.g1_s);
    utils.hashG1(transcriptHasher, curve, curContribution.delta.g1_sx);
    curContribution.transcript = transcriptHasher.digest();
    curContribution.delta.g2_sp = hashToG2(curve, curContribution.transcript);
    curContribution.delta.g2_spx = curve.G2.toAffine(curve.G2.timesFr(curContribution.delta.g2_sp, delta));
    curContribution.deltaAfter = delta1;
    curContribution.type = 0;
    mpcParams.contributions.push(curContribution);


    //////////
    /// Write COntribution
    //////////

    await fdTo.write(mpcParams.csHash);
    await fdTo.writeUBE32(mpcParams.contributions.length);

    for (let i=0; i<mpcParams.contributions.length; i++) {
        const c = mpcParams.contributions[i];
        await writeG1(c.deltaAfter);
        await writeG1(c.delta.g1_s);
        await writeG1(c.delta.g1_sx);
        await writeG2(c.delta.g2_spx);
        await fdTo.write(c.transcript);
    }

    const contributionHasher = Blake2b(64);
    hashPubKey(contributionHasher, curve, curContribution);

    const contributionHash = contributionHasher.digest();

    if (logger) logger.info(misc.formatHash(contributionHash, "Contribution Hash: "));

    await fdTo.close();
    await fdFrom.close();

    return contributionHash;

    async function copy(nBytes) {
        const CHUNK_SIZE = fdFrom.pageSize*2;
        for (let i=0; i<nBytes; i+= CHUNK_SIZE) {
            const n = Math.min(nBytes -i, CHUNK_SIZE);
            const buff = await fdFrom.read(n);
            await fdTo.write(buff);
        }
    }

    async function readG1() {
        const buff = await fdFrom.read(curve.G1.F.n8*2);
        return curve.G1.fromRprUncompressed(buff, 0);
    }

    async function readG2() {
        const buff = await fdFrom.read(curve.G2.F.n8*2);
        return curve.G2.fromRprUncompressed(buff, 0);
    }

    async function writeG1(P) {
        const buff = new Uint8Array(sG1);
        curve.G1.toRprUncompressed(buff, 0, P);
        await fdTo.write(buff);
    }

    async function writeG2(P) {
        const buff = new Uint8Array(sG2);
        curve.G2.toRprUncompressed(buff, 0, P);
        await fdTo.write(buff);
    }


}