Dart

Decrypt 256-bit AES GCM Produced by Something Unknown

See more Encryption Examples

Demonstrates how to decrypt something produced elsewhere (unknown) with 256-bit AES GCM. Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // This example assumes the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  // We have the following to decrypt:

  // Key (Base64): 
  final keyBase64 = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';

  // IV (Base64Url):
  final ivBase64Url = 'xrvaINMLqotAbWRK';

  // ciphertext (base64url):
  final cipherBase64Url = 'RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY=';

  final crypt = CkCrypt2();

  crypt.cryptAlgorithm = 'aes';
  crypt.cipherMode = 'gcm';
  crypt.keyLength = 256;

  crypt.setEncodedAad('random', 'ascii');
  crypt.setEncodedKey(keyBase64, 'base64');
  crypt.setEncodedIV(ivBase64Url, 'base64url');

  // The cipher text contains the 16-byte auth tag at the end.
  // get it separately..
  final bdEncrypted = CkBinData();
  final bdAuthTag = CkBinData();
  bdEncrypted.appendEncoded(cipherBase64Url, 'base64url');

  final numBytes = bdEncrypted.numBytes;
  final authTagHex = bdEncrypted.getEncodedChunk(numBytes - 16, 16, 'hex');

  print('Auth tag in hex: $authTagHex');

  bdAuthTag.appendEncoded(authTagHex, 'hex');
  bdEncrypted.removeChunk(numBytes - 16, 16);

  // Use this special value to tell Chilkat to ignore the auth tag.
  crypt.setEncodedAuthTag('FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF', 'hex');

  // Decrypt
  crypt.encodingMode = 'base64';
  try {
    final originalText = crypt.decryptStringENC(bdEncrypted.getEncoded('base64'));
    print(originalText);
    print('Success.');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
  }

  // Decrypted text
}