HaLo c5+ rndsig Verification Example

gistfile1.txt

// HaLo Core version 01.C5 onwards

// npm i --save elliptic sha.js
const EC = require('elliptic').ec;
const shajs = require('sha.js');
const ec = new EC('secp256k1');

// --- INPUT PARAMETERS ---
// just as they appear in the URL
const pk2 = "0481AD57A1D12B58D46DACE9746250725889EC7677CF865F5B02C9A0768DECB64FEE6F3CD094C86F7841A55C5286B256DF70986864CA788CF2AD91C5DBACC4BC72";
const rnd = "000000020A56B892CDC5A52E2964ACC88F79BFE6234BC864BE2ED2481E937398";
const rndsig = "3045022100B49164BEC8377DDE39BFDA54A8258578494CC562D75A4056E059A636760D68BD02202539D8A55DA3C652222387C208DC7BF72E07DA25042986F5B2A8ED2C1598327004";

// --- VERIFIER CODE ---
function verifyURLSig(pk2, rnd, rndsig) {
    const rndBuf = Buffer.from(rnd, "hex");

    if (rndBuf.length !== 32) {
        throw new Error("Incorrect length of the rnd parameter or hex decoding failure.");
    }

    const msgHashed = shajs('sha256')
        // static prefix: b'\x19Attest counter pk2:\n'.hex()
        .update(Buffer.concat([
            Buffer.from([0x19]),
            Buffer.from("Attest counter pk2:\n", "utf8"),
        ]))
        .update(rndBuf)
        .digest('hex');

    const sigBuf = Buffer.from(rndsig, "hex");

    if (sigBuf.length < 2 || 2 + sigBuf[1] > sigBuf.length) {
        throw new Error("Malformed signature in the rndsig field.");
    }

    const cutSig = sigBuf.subarray(0, 2 + sigBuf[1]).toString("hex");
    let key = null;

    try {
        key = ec.keyFromPublic(pk2, 'hex');
    } catch (e) {
        throw new Error("Unable to decode public key.");
    }

    const pk2Exported = key.getPublic(/* compact: */ false, 'hex');

    if (key.verify(msgHashed, cutSig)) {
        const counter = rndBuf.readUInt32BE(0);

        return {
            // always returns uncompressed public key
            "publicKey2": pk2Exported,
            // the scan counter that was validated
            "scanCounter": counter
        };
    } else {
        throw new Error("Failed to verify signature!");
    }
}

// --- USAGE ---
try {
    const validationResult = verifyURLSig(pk2, rnd, rndsig);
    console.log('The URL is correctly signed with:');
    console.log(validationResult);
} catch (e) {
    console.error('Failed to validate the URL\'s signature.');
}