Question

I have a program that has to encrypt an audio file and then decrypt it if needed. I tested my program on some other types of files, like .bin or .txt. The problem I get is that the decrypted file has some weird characters before the actual content, like the source file contains “010101” and after encryption-decryption it has “¬íw0w 010101”.

My encryption method code goes here:

public void cipherTheAudioFile(String fileDir, String fileToCipher) throws            FileNotFoundException, IOException, NoSuchAlgorithmException, InvalidKeySpecException,  InvalidKeyException, NoSuchPaddingException {
    File audioSourceFile = new File(fileDir + "\\" + fileToCipher);
    ObjectOutputStream oos = new ObjectOutputStream(
        new CipherOutputStream(new FileOutputStream(
            new java.io.File("").getAbsolutePath().toString() + "/encrypted/" + fileToCipher + ".sky"), cipher));

    byte[] audioFileInBytes = FileUtils.readFileToByteArray(audioSourceFile);
    oos.write(audioFileInBytes);

    fos = new FileOutputStream(KEY_FILE);
    SecretKeyFactory skf = SecretKeyFactory.getInstance(ENCRYPTION_ALGORITHM);
    DESKeySpec keyspec = (DESKeySpec) skf.getKeySpec(key, DESKeySpec.class);
    fos.write(keyspec.getKey());

    fos.close();
    oos.close();
}

My decryption method code goes here:

public void decryptTheAudioFile(String fileDir, String fileToDecipher) throws NoSuchAlgorithmException, NoSuchPaddingException, FileNotFoundException, IOException, ClassNotFoundException, InvalidKeySpecException, InvalidKeyException {
    fis = new FileInputStream(keyFile);
    byte[] keyspecbytes = new byte[fis.available()];

    File fileToWriteIn = createFileToWriteIn(fileDir, fileToDecipher);

    fis.read(keyspecbytes);
    SecretKeyFactory skf = SecretKeyFactory.getInstance(encryptionAlgorithm);
    DESKeySpec keyspec = new DESKeySpec(keyspecbytes);
    SecretKey key = skf.generateSecret(keyspec);
    Cipher cipher = Cipher.getInstance(encryptionAlgorithm);
    cipher.init(Cipher.DECRYPT_MODE, key);

    ObjectInputStream ois = new ObjectInputStream(
        new CipherInputStream(
            new FileInputStream(new java.io.File("").getAbsolutePath().toString() + "/encrypted/" + fileToDecipher + ".sky"), cipher));
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(fileToWriteIn));

    byte[] audioFileInBytes = new byte[1024];

    int numRead = 0;
    while ((numRead = ois.read(audioFileInBytes)) >= 0) {
        oos.write(audioFileInBytes, 0, numRead);
    }

    oos.close();
    fis.close();
    ois.close();
}

P.S. It could be something with the encoding, but I am not really sure.

EDITED

Ok, I have changed to the FileWriters, but still no change. Here goes the code:

 OutputStream os = new FileOutputStream(new java.io.File("").getAbsolutePath().toString() + "/encrypted/" + fileToCipher + ".sky");
    CipherInputStream cis = new CipherInputStream(new FileInputStream(audioSourceFile), cipher);
    byte[] audioFileInBytes = new byte[1024];
    int numRead = 0;
    while ((numRead = cis.read(audioFileInBytes)) >= 0) {
            os.write(audioFileInBytes, 0, numRead);
    }

Likewise goes the decryptor.

Answer 1

The problem is in the way that the decryptTheAudioFile method writes the file. Specifically, the problem is that it is using an ObjectOutputStream. That is adding an object serialization header. But it doesn’t belong there at all.

The solution is to get rid of this from decryptTheAudioFile:

ObjectOutputStream oos = new ObjectOutputStream(
         new FileOutputStream(fileToWriteIn));

and replace it with this:

OutputStream os = new FileOutputStream(fileToWriteIn);

and change the rest of the code to write to os. Your code needs to mirror how you are reading the file in cipherTheAudioFile.

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It would be a good idea to get rid of the other ObjectStream instances too and simply read and write to plain Streams. The other ObjectStreams are harmless (mostly), but they don’t actually achieve anything.