Use Dart instead of Go implement the XEdDSA signature

[crossle]

Now we use Dart ffi call Go for XEdDSA signature, we should use Dart implement it

Uint8List sha512HashFunc(Uint8List m) {
  var digest = sha512.convert(m).bytes;
  digest[0] &= 248;
  digest[31] &= 127;
  digest[31] |= 64;
  return digest;
}

Uint8List signature(Uint8List privateKey, Uint8List message, Uint8List random) {
  var pk = Ed25519.publickey(sha512HashFunc, privateKey);
  // Calculate r
  var diversifier = Uint8List.fromList([
    0xFE,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF,
    0xFF
  ]);

  var output = new AccumulatorSink<Digest>();
  var input = sha512.startChunkedConversion(output);
  input.add(diversifier);
  input.add(privateKey);
  input.add(message);
  input.add(random);
  input.close();
  var r = output.events.single.bytes;

[Tougee]

#5