javax.crypto.BadPaddingException

Question

我正在研究AES算法,我有这个例外,我无法解决.

javax.crypto.BadPaddingException: Given final block not properly padded
at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
at com.sun.crypto.provider.AESCipher.engineDoFinal(DashoA13*..)
at javax.crypto.Cipher.doFinal(DashoA13*..)

异常发生在解密部分.我在与解密算法不同的地方初始化密钥

KeyGenerator kgen = KeyGenerator.getInstance("AES");//key generation for AES
kgen.init(128); // 192 and 256 bits may not be available

然后我用我从文件中读取的密文传递给下面的方法

 public String decrypt(String message, SecretKey skey) {

    byte[] raw = skey.getEncoded();
    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
    // Instantiate the cipher
    Cipher cipher;

    byte[] original = null;
    try {
        cipher = Cipher.getInstance("AES");

        cipher.init(Cipher.DECRYPT_MODE, skeySpec);
        System.out.println("Original string: "
                + message);
        original = cipher.doFinal(message.trim().getBytes());  //here where I got the exception
        String originalString = new String(original);
       }
 //catches

编辑 这里是加密方法.

public String encrypt(String message, SecretKey skey) {
    byte[] raw = skey.getEncoded();
    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");

    // Instantiate the cipher

    Cipher cipher;
    byte[] encrypted = null;
    try {
        cipher = Cipher.getInstance("AES");

        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

        encrypted = cipher.doFinal(message.getBytes());
        System.out.println("raw is " + encrypted);

    } catches
    return asHex(encrypted);
}

这是asHex方法

  public static String asHex(byte buf[]) {
    StringBuffer strbuf = new StringBuffer(buf.length * 2);
    int i;

    for (i = 0; i < buf.length; i++) {
        if (((int) buf[i] & 0xff) < 0x10) {
            strbuf.append("0");
        }

        strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
    }

    return strbuf.toString();
}

这是我从文件中读取密文的地方

static public String readFile(String filePath) {
    StringBuilder file = new StringBuilder();
    String line = null;
    try {
        FileReader reader = new FileReader(filePath);
        BufferedReader br = new BufferedReader(reader);
        if (br != null) {
            line = br.readLine();
            while (line != null) {
                file.append(line);
                //      System.out.println("line is " + line);
                line = br.readLine();

            }
        }
        br.close();
        reader.close();
    } catch (IOException ex) {
        Logger.getLogger(FileManagement.class.getName()).log(Level.SEVERE, null, ex);
    }
    System.out.println("line is " + file.toString());
    return String.valueOf(file);

}

有人可以帮忙吗？

Answer 1

好吧,问题是您正在将加密的字节转换为十六进制字符串(使用该asHex方法),但是没有正确地将十六进制字符串转换回字节数组以进行解密.你不能使用getBytes.

您可以使用以下方法将十六进制字符串转换为字节数组:

public static byte[] fromHexString(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                             + Character.digit(s.charAt(i+1), 16));
    }
    return data;
}

然后更改您的解密方法以使用:

original = cipher.doFinal(fromHexString(message));

Answer 2

我确实有一个错误的填充异常，并且无法在互联网上找到解决我的问题的方法。由于我是经过一段时间的努力才找到的，所以我把它放在这里。

我的问题是，我正在读取硬盘驱动器上的文件，并通过缓冲区对其进行加密，始终调用 doFinal() 方法而不是 update() 方法。所以在解密时，我有填充错误

    input = new FileInputStream(file);
    output = new FileOutputStream(newFile);

    Cipher cipher = Cipher.getInstance("DES");
    cipher.init(Cipher.ENCRYPT_MODE, mySecretKey);

    byte[] buf = new byte[1024];

    count = input.read(buf);
    while (count >= 0) {
        output.write(cipher.update(buf, 0, count)); // HERE I WAS DOING doFinal() method
        count = input.read(buf);
    }
    output.write(cipher.doFinal()); // AND I DID NOT HAD THIS LINE BEFORE
    output.flush();

解密时，使用相同的方法，但使用带有 DECRYPT_MODE 的 Cipher init

    input = new FileInputStream(file);
    output = new FileOutputStream(newFile);

    Cipher cipher = Cipher.getInstance("DES");
    cipher.init(Cipher.DECRYPT_MODE, mySecretKey);

    byte[] buf = new byte[1024];

    count = input.read(buf);

    while (count >= 0) {
        output.write(cipher.update(buf, 0, count)); // HERE I WAS DOING doFinal() method

        //AND HERE WAS THE BadPaddingExceotion -- the first pass in the while structure

        count = input.read(buf);
    }
    output.write(cipher.doFinal()); // AND I DID NOT HAD THIS LINE BEFORE
    output.flush();

编写代码后，我不再有任何 BadPaddingException。

我可以确切地说，只有当原始清晰文件长度（通过 file.length() 获得）大于缓冲区时才会出现此异常。否则，我们不需要在 while 结构中多次传递，我们可以使用 doFinal() 调用一次加密。这证明了跟随您尝试加密的文件大小的异常的随机字符是合理的。

我希望你有一个很好的阅读！