How to encrypt and decrypt using AES CBC 256bit and PKCS5Padding in dart and also retrieve parameters

Here's a working example of encode in Java, decode in pointycastle.

Java

String plainText = "Hello World!";KeyGenerator generator = KeyGenerator.getInstance("AES");generator.init(256);SecretKey secret = generator.generateKey();Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");cipher.init(Cipher.ENCRYPT_MODE, secret);byte[] encodedData = cipher.doFinal(Base64.getEncoder().encode(plainText.getBytes(StandardCharsets.UTF_8)));Base64.Encoder encoder = Base64.getEncoder();System.out.println(encoder.encodeToString(secret.getEncoded()));System.out.println(encoder.encodeToString(cipher.getParameters().getEncoded())); // the DER encoded IVSystem.out.println(encoder.encodeToString(encodedData));

Dart

import 'dart:convert';import 'dart:typed_data';import 'package:pointycastle/export.dart';void main() {  // the following 3 values were output from the above Java code  var key = base64.decode('9JYmap3xB79oyBkY6ZIdJCXaOr/CurCK8XUsRZL9XXI=');  var params = base64.decode('BBChkSMIq/v35PRRWAJGwtTr');  var cipherText =      base64.decode('Dh+lg2IMzcLC0toDRSoNMAQoR7MWKMLMPRi7KtdQdmw=');  var iv = params.sublist(2); // strip the 4, 16 DER header  var cipher = PaddedBlockCipherImpl(    PKCS7Padding(),    CBCBlockCipher(AESFastEngine()),  );  cipher.init(    false /*decrypt*/,    PaddedBlockCipherParameters<CipherParameters, CipherParameters>(      ParametersWithIV<KeyParameter>(KeyParameter(key), iv),      null,    ),  );  var plainishText = cipher.process(cipherText);  print(utf8.decode(base64.decode(utf8.decode(plainishText))));}

Encrypting in Dart

  var key = Uint8List(32); // the 256 bit key  var plainText = 'Ciao Mondo';  var random = Random.secure();  var params = Uint8List(18)    ..[0] = 4    ..[1] = 16;  for (int i = 2; i < 18; i++) {    params[i] = random.nextInt(256);  }  var iv = params.sublist(2);  var cipher = PaddedBlockCipherImpl(    PKCS7Padding(),    CBCBlockCipher(AESFastEngine()),  )..init(      true /*encrypt*/,      PaddedBlockCipherParameters<CipherParameters, CipherParameters>(        ParametersWithIV<KeyParameter>(KeyParameter(key), iv),        null,      ),    );  var plainBytes = utf8.encode(base64.encode(utf8.encode(plainText)));  var cipherText = cipher.process(plainBytes);  // cipherText is the cipher text  // params is the Java compatible params