eccsecp256k1.ts

// secp256k1

import * as bigintConversion from "bigint-conversion";

function concatUint8Array(a: Uint8Array, b: Uint8Array): Uint8Array {
  const merged = new Uint8Array(a.length + b.length);
  merged.set(a);
  merged.set(b, a.length);
  return merged;
}

function randIntInRange(range: bigint): bigint {
  const buf = bigintConversion.bigintToBuf(range, true) as ArrayBuffer;
  const u8a = new Uint8Array(buf).slice(1);
  const randVal = crypto.getRandomValues(u8a);
  return bigintConversion.bufToBigint(
    concatUint8Array(new Uint8Array([(Math.random() * (u8a[0] - 0b10000000)) | 0]), randVal)
  );
}

function extendedGcd(
  a: bigint,
  b: bigint
): { result: bigint; x: bigint; y: bigint } {
  if (a === 0n) {
    return { result: b, x: 0n, y: 1n };
  }

  const { result, x: x1, y: y1 } = extendedGcd(b % a, a);

  return { result, x: y1 - (b / a) * x1, y: x1 };
}

function fastModularInverse(a: bigint, m: bigint): bigint {
  const { result: g, x } = extendedGcd(a, m);
  if (g != 1n) {
    throw new Error("Inverse does not exist!");
  }

  return ((x % m) + m) % m;
}

const n =
  115792089237316195423570985008687907852837564279074904382605163141518161494337n;

const G = {
  x: 55066263022277343669578718895168534326250603453777594175500187360389116729240n,
  y: 32670510020758816978083085130507043184471273380659243275938904335757337482424n,
};

function sign(privKey: bigint, hash: bigint): { r: bigint; s: bigint } {
  const k = randIntInRange(n);
  const r = (k * G.x) % n;
  const s = (fastModularInverse(k, n) * (hash + r * privKey)) % n;
  return { r, s };
}

function verify(
  pubKey: { x: bigint; y: bigint },
  hash: bigint,
  { r, s }: { r: bigint; s: bigint }
): boolean {
  const u1 = hash * fastModularInverse(s, n);
  const u2 = r * fastModularInverse(s, n);
  const x = u1 * G.x + u2 * pubKey.x;
  return r % n === x % n;
}

const privKey = randIntInRange(n);

const pubKey = {
  x: privKey * G.x,
  y: privKey * G.y,
};

console.log(pubKey);
console.log("Computing");

let v = new Uint8Array(256 / 8);
v = crypto.getRandomValues(v);

const signature = sign(privKey, bigintConversion.bufToBigint(v));

console.log(verify(pubKey, bigintConversion.bufToBigint(v), signature));

export {};