Java AES加解密报错：javax.crypto.IllegalBlockSizeException求助

我是Java AES开发新手，学习256位AES加解密时遇到如下错误：

Exception in thread "main" javax.crypto.IllegalBlockSizeException: Message must be a multiple of the block size without padding

测试输入"hello"或"dFet4Q2fi"都会触发该错误，目前对错误根源及代码修改方向感到困惑，仅了解AES/CBC/PKCS5Padding代表算法/模式/填充方式。

我的代码实现 #

main方法 #

public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeyException, NoSuchPaddingException, InvalidAlgorithmParameterException, BadPaddingException, IllegalBlockSizeException, InvalidKeySpecException {
        System.out.println("Encrypt/Decrypt a string");
        //3 params for AES algo: (1) input data, (2) secret key, (3) and IV
        Scanner scanner = new Scanner(System.in);
        String inputKey;
        int inputSecretKey = 256;
        IvParameterSpec IV;
        
        
        //step 1: input
        System.out.print("Input: ");
        inputKey = scanner.nextLine();
        
        //step 2: generate secret key

        System.out.println("Generating secret key with size "+inputSecretKey);
        SecretKey secretKey1 = generateKey(inputSecretKey);
        
        //step 3: generate IV
        IV = generateIv();
        
        //step 4: print
        String cipherText = encrypt("AES/CBC/PKCS5Padding", inputKey, secretKey1, IV);
        String plainText = decrypt("AES/CBC/PKCS5Padding", inputKey, secretKey1, IV);
        Assertions.assertEquals(inputKey, plainText);
        System.out.println("Encrypted: "+cipherText+" [size : "+cipherText.length()+"]");
        System.out.println("Decrypted: "+plainText+" [size : "+plainText.length()+"]");
        
        
        scanner.close();
        
    }

generateKey方法 #

public static SecretKey generateKey(int n) throws NoSuchAlgorithmException {
        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(n);
        SecretKey key = keyGen.generateKey();
        return key;
    }

generateIv方法 #

public static IvParameterSpec generateIv() {
        byte[] iv = new byte[16];
        new SecureRandom().nextBytes(iv);
        return new IvParameterSpec(iv);
    }

encrypt方法 #

public static String encrypt(String algorithm, String input, SecretKey key,
            IvParameterSpec iv) throws NoSuchPaddingException, NoSuchAlgorithmException,
            InvalidAlgorithmParameterException, InvalidKeyException,
            BadPaddingException, IllegalBlockSizeException {
            
            Cipher cipher = Cipher.getInstance(algorithm);
            cipher.init(Cipher.ENCRYPT_MODE, key, iv);
            byte[] cipherText = cipher.doFinal(input.getBytes());
            return Base64.getEncoder()
                .encodeToString(cipherText);
    }

decrypt方法（报错行标注） #

public static String decrypt(String algorithm, String cipherText, SecretKey key,
            IvParameterSpec iv) throws NoSuchPaddingException, NoSuchAlgorithmException,
            InvalidAlgorithmParameterException, InvalidKeyException,
            BadPaddingException, IllegalBlockSizeException {
            
            Cipher cipher = Cipher.getInstance(algorithm);
            cipher.init(Cipher.DECRYPT_MODE, key, iv);
            byte[] plainText = cipher.doFinal(Base64.getDecoder()
                .decode(cipherText)); //<-------- 此处报错
            return new String(plainText);
        }

错误根源与修复方案 #

你犯了一个基础的参数传递错误：在main方法调用decrypt时，传入的第二个参数是原始明文inputKey，而不是加密后得到的cipherText！

// 错误代码：
String plainText = decrypt("AES/CBC/PKCS5Padding", inputKey, secretKey1, IV);
// 正确代码：
String plainText = decrypt("AES/CBC/PKCS5Padding", cipherText, secretKey1, IV);

decrypt方法要求第二个参数是Base64编码的密文，但你传入了明文字符串，Base64解码后的字节数组长度几乎不可能是AES块大小（16字节）的整数倍，因此触发了IllegalBlockSizeException。

修正该参数后，代码即可正常运行。另外补充两点注意事项：

• 加密和解密必须使用同一个IV（当前代码已满足该要求）
• JDK8及以下版本使用256位AES需安装JCE扩展，新版本JDK默认已支持256位密钥

内容的提问来源于stack exchange，提问作者essinaya