Java - Decrypted string using XOR not producing original/encrypted string

Question

I've been provided with specific steps regarding encryption which is essentially converting a string to a byte array and "XORing" each byte array element with a specific number and converting this new byte array to a string.

As for the decryption I'm to reconvert the decrypted string into a byte array, take each element XOR this with the number used in the encryption and convert the new decrypted array to a string to give me the exact string i started with.

Unfortunately I'm unable to do obtain the string I started with e.g. when i attempt encrypting 6,7,8,9,10 the decryption returns B@722b9406 not 6,7,8,9,10. Any ideas why this is so?

My ENCRYPTION CODE is below:

    //Take each array element and do "Exclusive or" with "50" 
public void XORUnencryptedByteArray() {
    System.out.println("\nPART 3:\nXORUnencryptedByteArray() - " + "UnencryptedStringAsByteArray.length IS: " + UnencryptedStringAsByteArray.length);

    byte[] UnencryptedByteArraybyXOR = new byte[UnencryptedStringAsByteArray.length];

    int XOR_Value = 50;

    byte XOR_Value_as_byte = (byte) XOR_Value;

    System.out.println("\nPART 3:\nXORUnencryptedByteArray() - " + "XOR_Value_as_byte IS: " + XOR_Value_as_byte + "\n");

    for ( int j = 0; j < UnencryptedStringAsByteArray.length; j++ ) {

        System.out.println("\nPOSITION " + j + " OF UnencryptedStringAsByteArray[j] CONTAINS: " + UnencryptedStringAsByteArray[j]);

        System.out.println("\n" + UnencryptedStringAsByteArray[j] + " ^ " + XOR_Value_as_byte + " IS: " + (UnencryptedStringAsByteArray[j] ^ XOR_Value_as_byte));

    }

            for (int i = 0; i < UnencryptedByteArraybyXOR.length; i++) { 

                    UnencryptedByteArraybyXOR[i] = (byte) (UnencryptedStringAsByteArray[i] ^ XOR_Value_as_byte);

                System.out.println( "\nPOSITION " + i + " OF UnencryptedByteArraybyXOR[i] IS: " + UnencryptedByteArraybyXOR[i]);    
            }

    //Collect all encrypted array elements and convert the byte array to string
    System.out.println("\nUnencryptedByteArraybyXOR.length IS: " + UnencryptedByteArraybyXOR.length);

    System.out.println("\nUnencryptedByteArraybyXOR.toString() AS STRING IS: " + UnencryptedByteArraybyXOR.toString());

    UnencryptedByteArraybyXORAsString = new String(UnencryptedByteArraybyXOR);

    //System.out.println("\nUnencryptedByteArraybyXORAsString IS: " + UnencryptedByteArraybyXORAsString);   

    WriteStringToFile(UnencryptedByteArraybyXOR.toString());


}

public void WriteStringToFile(String UnencryptedByteArraybyXORAsString) {
        try {
            String str = UnencryptedByteArraybyXORAsString;
            File newTextFile = new File("/Users/anmonari/Desktop/textfile.txt");

            FileWriter fw = new FileWriter(newTextFile);
            fw.write(str);
            fw.close();

        } catch (IOException iox) {
            //do stuff with exception
            iox.printStackTrace();
        }

}

my DECRYPTION code is below:

 public void XORDecryptedByteArray(byte[] encryptedStringAsByteArray) {

    System.out.println("\nXORencryptedByteArray() - " + "encryptedStringAsByteArray.length IS: " + encryptedStringAsByteArray.length);

    byte[] encryptedByteArraybyXOR = new byte[encryptedStringAsByteArray.length];

    int XOR_Value = 50;

    byte XOR_Value_as_byte = (byte) XOR_Value;

    System.out.println("\nXORencryptedByteArray() - " + "XOR_Value_as_byte IS: " + XOR_Value_as_byte + "\n");

    for ( int j = 0; j < encryptedStringAsByteArray.length; j++ ) {

        System.out.println("\n" + encryptedStringAsByteArray[j] + " ^ " + XOR_Value_as_byte + " IS: " + (encryptedStringAsByteArray[j] ^ XOR_Value_as_byte));

    }

            for (int i = 0; i < encryptedByteArraybyXOR.length; i++) { 

                  encryptedByteArraybyXOR[i] = (byte) (encryptedStringAsByteArray[i] ^ XOR_Value_as_byte);

                  System.out.println("\n" + "POSITION " + i + " OF encryptedByteArraybyXOR[i] CONTAINS: " + encryptedByteArraybyXOR[i]);    
            }

    System.out.println("\ndecryptedByteArraybyXOR.length IS: " + encryptedByteArraybyXOR.length);

    System.out.println("\ndecryptedByteArraybyXOR.toString() AS STRING IS: " + encryptedByteArraybyXOR.toString());

 }

ANY ASSISTANCE IS APPRECIATED !!!!!

Is there a reason that you're not just using KeyCzar for your crypto needs? — Matt Ball
– Matt Ball, Commented Feb 25, 2013 at 15:29

Jon Skeet · Accepted Answer · 2013-02-25 17:37:13Z

3

This is the main problem:

UnencryptedByteArraybyXORAsString = new String(UnencryptedByteArraybyXOR);

You're treating a arbitrary binary data as if it were a string. It's not. You must not create a new string from a byte array which isn't actually encoded binary data.

If you really want to convert an arbitrary byte array to a string in a reversible manner, use base64.

Additionally, when you print out a byte array by just calling toString on it, you'll get exactly a value such as "B@722b9406". That's not a matter of data loss - it's just the way that arrays are converted to strings. Use Arrays.toString(byte[]) to perform a more useful conversion.

Finally, I hope you weren't planning on using this "encryption" for anything sensitive - it's obfuscation at best.

edited Feb 25, 2013 at 17:37

answered Feb 25, 2013 at 15:31

Jon Skeet

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2 Comments

Maarten Bodewes Over a year ago

Glad to see the venerable Jon Skeet struggle with the link encoding of methods too sometimes :) +1 of course

Jon Skeet Over a year ago

@owlstead: It was fine before I hit Ctrl-L :)

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