@covenance/dlc/dist/crypto/general.js

Crypto and Bitcoin functions for Covenance DLC implementation

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.verifySig = verifySig;
exports.verifySigStrict = verifySigStrict;
exports.encodeXOnlyPubkey = encodeXOnlyPubkey;
exports.mod = mod;
const secp256k1_1 = require("./secp256k1");
const utils_1 = require("../utils");
/**
 * Function to verify a general signature
 * @param sig - The signature to verify
 * @param pubKey - The public key to verify against
 * @param message - The message that was signed
 * @param tag - The tag to use for hashing (defaults to BIP0340/challenge)
 * @returns Boolean indicating whether the signature is valid
 */
async function verifySig(sig, pubKey, message, tag = Uint8Array.from(Buffer.from('7bb52d7a9fef58323eb1bf7a407db382d2f3f2d81bb1224f49fe518f6d48d37c', 'hex')) // SHA256('BIP0340/challenge')
) {
    // Compute H(tag||tag||R||P||m)
    const hashInput = new Uint8Array([
        ...tag,
        ...tag,
        ...sig.R.toRawBytes(true).slice(1),
        ...pubKey.toRawBytes(true).slice(1),
        ...message
    ]);
    const hash = await (0, utils_1.sha256)(hashInput);
    const e = mod(BigInt('0x' + (0, utils_1.bytesToHex)(hash)), secp256k1_1.CURVE.n);
    // Compute s * G
    const sG = secp256k1_1.Point.BASE.multiply(sig.s);
    // Compute R + e * P
    const rightSide = sig.R.add(pubKey.multiply(e));
    // Verify s * G = R + e * P
    return sG.equals(rightSide);
}
/**
 * Function to verify a signature with additional script interpreter like verification
 * @param sig - The signature to verify
 * @param pubKey - The public key to verify against
 * @param message - The message that was signed
 * @param tag - The tag to use for hashing (defaults to BIP0340/challenge)
 * @returns Boolean indicating whether the signature is valid
 */
async function verifySigStrict(sig, pubKey, message, tag = Uint8Array.from(Buffer.from('7bb52d7a9fef58323eb1bf7a407db382d2f3f2d81bb1224f49fe518f6d48d37c', 'hex')) // SHA256('BIP0340/challenge')
) {
    // First do basic signature verification
    const basicVerification = await verifySig(sig, pubKey, message, tag);
    if (!basicVerification)
        return false;
    // Perform additional script interpreter like verification
    const r = sig.R.x;
    const s = sig.s;
    if (r >= secp256k1_1.CURVE.P || s >= secp256k1_1.CURVE.n) {
        return false;
    }
    const hashInput = new Uint8Array([
        ...tag,
        ...tag,
        ...sig.R.toRawBytes(true).slice(1),
        ...pubKey.toRawBytes(true).slice(1),
        ...message
    ]);
    const hash = await (0, utils_1.sha256)(hashInput);
    const e = mod(BigInt('0x' + (0, utils_1.bytesToHex)(hash)), secp256k1_1.CURVE.n);
    const sG = secp256k1_1.Point.BASE.multiply(sig.s);
    const R = sG.add(pubKey.multiply(e).negate());
    if (!(R.y % 2n === 0n) ||
        !(R.x === r)) {
        return false;
    }
    return true;
}
/**
 * Encodes a point as a BIP-340 x-only key
 * @param point - The point to encode
 * @returns The encoded point as a 32-byte Buffer
 */
function encodeXOnlyPubkey({ x, y }) {
    if (y & 1n)
        y = secp256k1_1.CURVE.P - y; // even-y representative
    if (x < 0n || x >= secp256k1_1.CURVE.P)
        throw new RangeError("x out of range");
    return Buffer.from(x.toString(16).padStart(64, "0"), "hex");
}
/**
 * Modulus operation that handles negative numbers
 * @param k - The number to mod
 * @param n - The modulus
 * @returns The modulus of k and n
*/
function mod(k, n) {
    return ((k % n) + n) % n;
}
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