tweakPublicKey static method

Map<String, dynamic>? tweakPublicKey(Uint8List publicKey, Uint8List tweak)

Tweaks a public key according to BIP-341 (Taproot).

publicKey: 32-byte x-only public key P. tweak: 32-byte tweak value t.

Computes Q = P + t*G. Returns Map { 'x': Uint8List(32), 'yParity': int (0 or 1) } Returns null if P is invalid or result is potentially invalid (rare).

Implementation

static Map<String, dynamic>? tweakPublicKey(
    Uint8List publicKey, Uint8List tweak) {
  if (publicKey.length != 32 || tweak.length != 32) {
    throw ArgumentError('Inputs must be 32 bytes');
  }

  final P = _liftX(publicKey);
  if (P == null) return null; // Invalid P

  final t = _bytesToBigInt(tweak);
  if (t >= _n) return null; // Invalid tweak

  // T = t * G
  final T = _scalarMult(t, [_Gx, _Gy]);

  // Q = P + T
  final Q = _pointAdd(P, T);

  if (Q[0] == BigInt.zero && Q[1] == BigInt.zero)
    return null; // Point at infinity

  final parity = _hasOddY(Q) ? 1 : 0;

  return {
    'x': _bigIntToBytes(Q[0], 32),
    'yParity': parity,
  };
}