Question

Hey guys I wanted to know if i could get a little help: Im trying to count up in hex inside of a byte array. What im doing is i have the plain text in the form of 8 hex numbers and the cipher text in the same form as well as the first 4 numbers of the key. And im trying to use the DES to crack the key via brute force.

my key looks like this:

[A3 BB 12 44 __ __ __ __]

and i want it to start like this i suppose:

[A3 BB 12 44 00 00 00 00]

then

[A3 BB 12 44 00 00 00 01]

and so on. I just dont really know how to count in hex. inside of a byte array at that!

any help is much appreciated!

EDITED AFTER MUCH HELP

here is find key ( i changed some of the names of things around to better suit my program)

public static void findKey(){

    byte [] keyBytes = null;
    byte [] pt;
    byte [] ct;

    codeBreaker KEY = new codeBreaker(new byte[]{(byte)0x01, (byte)0x23, (byte)0x45, (byte)0x67, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x00}, 2 );

    String plaintext = "Plaintxt";
    ct = new byte [] {(byte)0x4A, (byte)0xC4, (byte)0x55, (byte)0x3D, (byte)0xB3, (byte)0x37, (byte)0xCA, (byte)0xB3};

    //convert the plain text "Plaintxt" into a hex byte array
    String ptHex = asciiToHex(plaintext);
    pt = getBytes(ptHex);

    //keyBytes = KEY.inc()

    //my attempt
    /*while(!isKey(pt,keyBytes,ct)){
        KEY.inc(); // something like increase the key by 1 and send t back in.
    }
    */


    //this is your original while loop
    /*while (KEY.inc()) {
        byte[] bytes = KEY.getBytes();
        for (byte b: bytes) {
            System.out.printf("%02X ", b);
        }
        System.out.println();
    }
    */


    //Final outputs for the findKey method
    System.out.println("        Plain Text In Hex Is:");        
    printByteArray(pt);
    System.out.println();
    System.out.println("         The Cipher Text Is:");
    printByteArray(ct);
    System.out.println();

}

and here is the stuff you came up with

    public codeBreaker(byte[] keyAr, int startIndex) {
    this.key = keyAr;
    this.startIndex = startIndex;
}

   public boolean inc() {
   int i;
   for (i = key.length-1; i >= startIndex; i--) {
       key[i]++;
       if (key[i] != 0)
           break;
   }
        // we return false when all bytes are 0 again
   return (i >= startIndex || key[startIndex] != 0);
}

public byte[] getBytes() {
    return key;
}

which I all put into one class and called it codeBreaker with the rest of the methods i have (but those other ones dont have anything to do with this specific part)

Answer 1

What about this one?

public class ByteIncrement
{
    private final byte[] bytes;
    private final int startIndex;
    public ByteIncrement(byte[] bytes, int startIndex) {
        this.bytes = bytes;
        this.startIndex = startIndex;
    }
    public boolean inc() {
        int i;
        for (i = bytes.length-1; i >= startIndex; i--) {
            bytes[i]++;
            if (bytes[i] != 0)
                break;
        }
        // we return false when all bytes are 0 again
        return (i >= startIndex || bytes[startIndex] != 0);
    }
    public byte[] getBytes() {
        return bytes;
    }

    public static void main(String[] args) {
        ByteIncrement bi = new ByteIncrement(new byte[]{(byte)0xa4, 0x56, 0x17, (byte)0x9f, 0x00, 0x00, 0x00, 0x00}, 2 ); // first two bytes are constant -> 2
        while (bi.inc()) {
            byte[] bytes = bi.getBytes();
            for (byte b: bytes) {
                System.out.printf("%02X ", b);
            }
            System.out.println();
        }
    }
}