我有一个在Laravel PHP中加密的字符串。加密函数如下。

public function getEncryptedString()
{
    try {
            $m2 = Crypt::encryptString('Thismessagewillbeencrypted', 'theencryptionkey');
        return response()->json([
            'm2' => $m2 ? $m2 : null,
        ], 200);
    } catch (\Exception $e) {
        return response()->json([
            'message' => 'Something went wrong',
            'error' => $e->getMessage()
        ], 400);
    }
}

Flutter/dart如下所示。

import 'dart:convert';
import 'dart:typed_data';

import 'package:pointycastle/export.dart';

Uint8List aesCbcDecrypt(Uint8List key, Uint8List iv, Uint8List cipherText) {
  assert([128, 192, 256].contains(key.length * 8), 'Invalid key length.');
  assert(128 == iv.length * 8, 'Invalid IV length. IV must be 128 bits');
  assert(
    128 == cipherText.length * 8,
    'Invalid cipherText length. cipherText must be 128 bits.',
  );

  // Create a CBC block cipher with AES, and initialize with key and IV

  final cbc = CBCBlockCipher(AESEngine())
    ..init(false, ParametersWithIV(KeyParameter(key), iv)); // false=decrypt

  // Decrypt the cipherText block-by-block

  final paddedPlainText = Uint8List(cipherText.length); // allocate space

  var offset = 0;
  while (offset < cipherText.length) {
    offset += cbc.processBlock(cipherText, offset, paddedPlainText, offset);
  }
  assert(
    offset == cipherText.length,
    'Decryption process did not process the entire cipherText.',
  );

  return paddedPlainText;
}

void decrypter() {
  const encryptedString =
      'eyJpdiI6IjFLc001N25UNzhQNXVMOGxHMGZzeEE9PSIsInZhbHVlIjoiVmU0SGVVL0xFQUtCeW83NkVSSXpOZDRXWUV2allZTEg0c3J4aTJNV1BkST0iLCJtYWMiOiI2Yjk2MGQ3NzAzOTIwMjM5YTc5NTEwMjM2NWFlNDM1MTYwZDI5NzBjNjE4MWQzN2Q0OTE4NmZjNDUxZjNjZGUwIiwidGFnIjoiIn0=';

  const key = 'theencryptionkey';

  final json = jsonDecode(utf8.decode(base64Decode(encryptedString)));

  final decodedKey = base64Decode(key);
  final decodedIV = base64Decode(json['iv'] as String);
  final decodedCipherText = base64Decode(json['value'] as String);

  // Ensure cipherText has the correct length
  final cipherText =
      decodedCipherText.sublist(0, 16); // Take the first 16 bytes (128 bits)

  final result = aesCbcDecrypt(decodedKey, decodedIV, cipherText);

  print(base64.encode(result));
}

encryptedString是thecryptionkeykey加密Thismessagewillbeencrypted后得到的响应String。这当然是为了测试这个过程。

但是在测试用flutter dart代码解密加密字符串时，我不断得到不同的错误。我不明白我做错了什么。
有没有什么解密指南能帮上忙？
我使用的是pointycastle软件包，并遵循this。