buildServerHello function

Uint8List buildServerHello({ required Uint8List serverRandom, required Uint8List publicKey, required Uint8List sessionId, required int cipherSuite, required int group, })

Implementation

Uint8List buildServerHello({
  required Uint8List serverRandom,
  required Uint8List publicKey,
  required Uint8List sessionId,
  required int cipherSuite,
  required int group,
}) {
  final out = BytesBuilder();

  // --------------------------------------------------
  // Handshake body
  // --------------------------------------------------
  final body = BytesBuilder();

  // legacy_version = 0x0303
  body.add([0x03, 0x03]);

  // random (32 bytes)
  body.add(serverRandom);

  // legacy_session_id_echo
  body.addByte(sessionId.length & 0xff);
  body.add(sessionId);

  // cipher_suite
  body.add([(cipherSuite >> 8) & 0xff, cipherSuite & 0xff]);

  // legacy_compression_method = 0x00
  body.addByte(0x00);

  // --------------------------------------------------
  // Extensions
  // --------------------------------------------------
  final extensions = BytesBuilder();

  // supported_versions extension
  // type = 0x002b, len = 0x0002, value = 0x0304
  extensions.add([0x00, 0x2b, 0x00, 0x02, 0x03, 0x04]);

  // key_share extension
  final keyShareBody = BytesBuilder()
    ..add([(group >> 8) & 0xff, group & 0xff])
    ..add([(publicKey.length >> 8) & 0xff, publicKey.length & 0xff])
    ..add(publicKey);

  final keyShareBytes = keyShareBody.toBytes();

  extensions.add([
    0x00, 0x33, // extension type
    (keyShareBytes.length >> 8) & 0xff,
    keyShareBytes.length & 0xff,
    ...keyShareBytes,
  ]);

  final extBytes = extensions.toBytes();

  // extensions length
  body.add([(extBytes.length >> 8) & 0xff, extBytes.length & 0xff]);

  body.add(extBytes);

  final bodyBytes = body.toBytes();

  // --------------------------------------------------
  // Handshake wrapper
  // type = 0x02 (ServerHello)
  // length = uint24
  // --------------------------------------------------
  out.addByte(0x02);
  out.add([
    (bodyBytes.length >> 16) & 0xff,
    (bodyBytes.length >> 8) & 0xff,
    bodyBytes.length & 0xff,
  ]);
  out.add(bodyBytes);

  return out.toBytes();
}