decrypt method

@override Future<Uint8List> decrypt(Uint8List ivAndBytes, { Uint8List? publicKey, })

Decrypts the provided data using the public key.

Implementation

@override
Future<Uint8List> decrypt(
  Uint8List ivAndBytes, {
  Uint8List? publicKey,
}) async {
  // Extract the ephemeral public key and the encrypted data
  final ephemeralPublicKeyBytes = ivAndBytes.sublist(
    0,
    compressedPublicKeyLength,
  );
  final encryptedData = ivAndBytes.sublist(
    compressedPublicKeyLength,
  ); // The rest is the encrypted data

  Uint8List pubKeyToUse;
  if (publicKey == null) {
    pubKeyToUse = ephemeralPublicKeyBytes;
  } else {
    pubKeyToUse = publicKey;
  }

  final sharedSecret = await computeEcdhSecret(pubKeyToUse);

  final algorithm = crypto.Hkdf(hmac: crypto.Hmac.sha256(), outputLength: 32);
  final secretKey = crypto.SecretKey(sharedSecret);
  final derivedKey = await algorithm.deriveKey(
    secretKey: secretKey,
    nonce: staticHkdNonce,
  );

  final derivedKeyBytes = await derivedKey.extractBytes();

  var symmetricKey = Uint8List.fromList(derivedKeyBytes);

  final decryptedData = _encryptionUtils.decryptFromBytes(
    symmetricKey,
    encryptedData,
  );

  if (decryptedData == null) {
    throw SsiException(
      message: 'Decryption failed, bytes are null',
      code: SsiExceptionType.unableToDecrypt.code,
    );
  }

  return decryptedData;
}