java - 解密 AES/CBC/PKCS5Padding 错误 : Given final block not properly padded

Question

在大型加密文件上解密 AES/CBC/PKCS5Padding 密码时，我收到给出的最终 block 未正确填充错误。

我认为这个问题是由于在 cipher.init() 方法中添加错误的初始化 vector 引起的。

我无法在运行时读取整个文件，因此我需要加密固定大小的 block 。此时，我正在创建 IV 并将其存储到 .txt 文件中。但在解密方法中，我在每个解密周期都使用相同的 IV。我应该如何改变这个？

加密:

void encrypt() throws Exception{
    char[] password = passwordText.getText().toCharArray();
    byte[] salt = new byte[8];

    /* Creating and saving salt */
    salt = saveSalt(salt);

    /* Securing password */
    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
    KeySpec spec = new PBEKeySpec(password, salt, 65536, 128);
    SecretKey tmp = factory.generateSecret(spec);
    SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");

    if (choosedFile != null) {
        /* Choosing algorithm for decryption */
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

        /* Getting plain file */
        CipherInputStream fis = new CipherInputStream(new  FileInputStream(choosedFile), cipher);
        CipherOutputStream fos = new CipherOutputStream(new FileOutputStream(choosedFile+".encrypted"), cipher);

        /* Encrypting and Measuring */
        long startTime = System.currentTimeMillis();
        cipher.init(Cipher.ENCRYPT_MODE, secret);
        byte[] rawText = new byte[128];
        int count;
        while((count = fis.read(rawText)) > 0) {
            System.out.println(count);
            byte[] encryptedText = cipher.doFinal(rawText);
            fos.write(encryptedText, 0, count);
        }
        long stopTime = System.currentTimeMillis();

        fis.close();
        fos.close();

        /* Creating initialization vector and storing*/
        byte[] iVector = cipher.getIV();
        saveIVector(iVector);

        text.setText(text.getText() + "File was encrypted in " + (stopTime - startTime) + "ms.\n");
    }

}

解密:

    void decrypt() throws Exception {
    /* Getting salt */
    byte[] salt = getSalt();
    /* Getting initialization vector */
    byte[] iVector = getIVector();
    /* Getting user password */
    char[] password = passwordText.getText().toCharArray();


    /* Securing password */
    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
    KeySpec spec = new PBEKeySpec(password, salt, 65536, 128);
    SecretKey tmp = factory.generateSecret(spec);
    SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");

    if (choosedFile != null) {

        /* Choosing algorithm for decryption */
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        /* Getting ciphered file */


        CipherInputStream fis = new CipherInputStream(new  FileInputStream(choosedFile), cipher);
        CipherOutputStream fos = new CipherOutputStream(new FileOutputStream(choosedFile+".decrypted"), cipher);

        /* Decrypting and Measuring */
        long startTime = System.currentTimeMillis();
        cipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iVector));
        byte[] rawText = new byte[128];
        int count;
        while((count = fis.read(rawText)) > 0) {
                byte[] encryptedText = cipher.doFinal(rawText);
                fos.write(encryptedText, 0, count);
            }

        long stopTime = System.currentTimeMillis();

        fis.close();
        fos.close();

Answer 1

使用CipherInputStream和CipherOutputStream时，流处理对密码的所有调用(这就是您在初始化时将密码传递给它的原因)。您只需正确初始化它，并通过流传输数据，密码流将对 update() 和 doFinal() 进行所需的调用。请记住关闭 Steam 以触发 doFinal()。

目前，您的代码以不受控制的方式多次通过密码传递数据，并且数据困惑。

此外，您只需要一个 CipherInputStream 进行解密，以及一个 CipherOutputStream 进行加密。在您当前的代码中，您同时使用加密和解密。

加密可能是这样的(这不处理 iv ..):

...     
cipher.init(Cipher.ENCRYPT_MODE, secret);
InputStream is = new FileInputStream(choosedFile);
OutputStream os = new CipherOutputStream(new FileOutputStream(choosedFile+".encrypted"), cipher);

byte[] buffer = new byte[1024];
int len;
while ((len = is.read(buffer)) != -1) {
    os.write(buffer, 0, len);
}

is.close();
os.close();
...