elliptic_signing.js

elliptic_signing.js

EC.prototype.sign = function sign(msg, key, enc, options) {
  if (typeof enc === 'object') {
    options = enc;
    enc = null;
  }
  if (!options)
    options = {};

  key = this.keyFromPrivate(key, enc);
  msg = this._truncateToN(new BN(msg, 16));

  // Zero-extend key to provide enough entropy
  var bytes = this.n.byteLength();
  var bkey = key.getPrivate().toArray('be', bytes);

  // Zero-extend nonce to have the same byte size as N
  var nonce = msg.toArray('be', bytes);

  // Instantiate Hmac_DRBG
  var drbg = new HmacDRBG({
    hash: this.hash,
    entropy: bkey,
    nonce: nonce,
    pers: options.pers,
    persEnc: options.persEnc || 'utf8'
  });

  // Number of bytes to generate
  var ns1 = this.n.sub(new BN(1));

  for (var iter = 0; true; iter++) {
    var k = options.k ?
        options.k(iter) :
        new BN(drbg.generate(this.n.byteLength()));
    k = this._truncateToN(k, true);
    if (k.cmpn(1) <= 0 || k.cmp(ns1) >= 0)
      continue;

    var kp = this.g.mul(k);
    if (kp.isInfinity())
      continue;

    var kpX = kp.getX();
    var r = kpX.umod(this.n);
    if (r.cmpn(0) === 0)
      continue;

    var s = k.invm(this.n).mul(r.mul(key.getPrivate()).iadd(msg));
    s = s.umod(this.n);
    if (s.cmpn(0) === 0)
      continue;

    var recoveryParam = (kp.getY().isOdd() ? 1 : 0) |
                        (kpX.cmp(r) !== 0 ? 2 : 0);

    // Use complement of `s`, if it is > `n / 2`
    if (options.canonical && s.cmp(this.nh) > 0) {
      s = this.n.sub(s);
      recoveryParam ^= 1;
    }

    return new Signature({ r: r, s: s, recoveryParam: recoveryParam });
  }
};