sign method

Uint8List sign(Uint8List message)

Implementation

Uint8List sign(Uint8List message) {
  Curve curve = this.curve;
  Point generator = curve.generator;
  BigInt order = curve.order;

  Uint8List h = this._hashPrivateKey();
  Uint8List leftHalf = h.sublist(0, this.curve.keySize);

  Uint8List s = _getPrivateScalar(leftHalf);

  Point A = _getPublicKeyPoint(s);

  Uint8List prefix = _getSignaturePrefix(h);

  Shake256 hash = curve.hash;
  Uint8List curveSigner;

  if (curve.curveName == 'Ed448') {
    String m = 'SigEd448' + String.fromCharCodes([0x00, 0x00]);
    curveSigner = Uint8List.fromList(m.codeUnits);
  } else if (curve.curveName == 'Ed521') {
    String m = 'SigEd521' + String.fromCharCodes([0x00, 0x00]);
    curveSigner = Uint8List.fromList(m.codeUnits);
  } else {
    throw Exception("Curve not supported");
  }

  hash.update(curveSigner);
  hash.update(prefix);
  hash.update(message);
  Uint8List r = hash.digest(curve.signatureSize);

  r = toLittleEndian(r);

  BigInt rBigInt = decodeBigInt(r);
  rBigInt = rBigInt % order;

  r = encodeBigInt(rBigInt, curve.signatureSize);

  Point pointR = generator.mul(r);

  Uint8List R = curve.encodePoint(pointR);

  // Compute S
  Uint8List eA = curve.encodePoint(A);

  hash.update(curveSigner);
  hash.update(R);
  hash.update(eA);
  hash.update(message);
  Uint8List k = hash.digest(curve.signatureSize);

  k = toLittleEndian(k);

  BigInt reducedK = decodeBigInt(k) % order;
  Uint8List S = encodeBigInt(
      (decodeBigInt(r) + (reducedK * decodeBigInt(s))) % order,
      curve.keySize);

  S = toLittleEndian(S);

  return Uint8List.fromList(R + S);
}