aesDecrypt method

Implementation

Uint8List aesDecrypt(Uint8List data) {
  AesCryptArgumentError.checkNullOrEmpty(
      _aesKey, 'AES encryption key null or is empty.');
  if (_aesMode != AesMode.ecb && _aesIV.isEmpty) {
    throw AesCryptArgumentError(
        'The initialization vector is empty. It can not be empty when AES mode is not ECB.');
  } else if (data.length % 16 != 0) {
    throw AesCryptArgumentError(
        'Invalid data length for AES: ${data.length} bytes.');
  }

  Uint8List decData = Uint8List(data.length); // returned decrypted data;
  Uint8List t = Uint8List(16); // 16-byte block
  Uint8List x_block;
  Uint8List block16 = Uint8List.fromList(
      _aesIV); // 16-byte block to hold the temporary output of the cipher

  switch (_aesMode) {
    case AesMode.ecb:
      for (int i = 0; i < data.length; i += 16) {
        for (int j = 0; j < 16; ++j) {
          if ((i + j) < data.length) {
            t[j] = data[i + j];
          } else {
            t[j] = 0;
          }
        }
        x_block = aesDecryptBlock(t);
        decData.setRange(i, i + 16, x_block);
      }
      break;
    case AesMode.cbc:
      for (int i = 0; i < data.length; i += 16) {
        for (int j = 0; j < 16; ++j) {
          if ((i + j) < data.length) {
            t[j] = data[i + j];
          } else {
            t[j] = 0;
          }
        }
        x_block = aesDecryptBlock(t);
        // XOR the iv/previous cipher block with this decrypted cipher block
        for (int j = 0; j < 16; ++j) {
          x_block[j] = x_block[j] ^ block16[j];
        }
        block16 = Uint8List.fromList(t);
        decData.setRange(i, i + 16, x_block);
      }
      break;
    case AesMode.cfb:
      for (int i = 0; i < data.length; i += 16) {
        // Encrypt the initialization vector/cipher output then XOR with the ciphertext
        x_block = aesEncryptBlock(block16);
        for (int j = 0; j < 16; ++j) {
          // XOR the cipher output with the ciphertext.
          x_block[j] = ((i + j) < data.length ? data[i + j] : 0) ^ x_block[j];
          block16[j] = data[i + j];
        }
        decData.setRange(i, i + 16, x_block);
      }
      break;
    case AesMode.ofb:
      decData = aesEncrypt(data);
      break;
  }
  return decData;
}