//******************************************************************************
//
// File: FindKeySeq2.java
// Package: edu.rit.clu.keysearch
// Unit: Class edu.rit.clu.keysearch.FindKeySeq2
//
// This Java source file is copyright (C) 2009 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
// A PARTICULAR PURPOSE. See the GNU General Public License for more details.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************
package edu.rit.clu.keysearch;
import edu.rit.crypto.blockcipher.AES256Cipher;
import edu.rit.pj.Comm;
import edu.rit.util.Hex;
/**
* Class FindKeySeq2 is a sequential program that solves an AES partial key
* search problem. The program's command line arguments are the plaintext
* (128-bit hexadecimal number), the ciphertext (128-bit hexadecimal number),
* the partial key with the n least significant bits set to 0 (256-bit
* hexadecimal number), and n, the number of key bits to search for. The
* ciphertext was created by encrypting the plaintext with the key; however, not
* all bits of the key are provided. The problem is to find the complete key.
* The program performs an exhaustive search, trying all possible values for the
* missing key bits until it finds the key that reproduces the given ciphertext
* from the given plaintext.
*
* Usage: java edu.rit.clu.keysearch.FindKeySeq2 plaintext
* ciphertext partialkey n
*
plaintext = Plaintext (128-bit hexadecimal number)
*
ciphertext = Ciphertext (128-bit hexadecimal number)
*
partialkey = Partial key (256-bit hexadecimal number)
*
n = Number of key bits to search for
*
* Whereas class {@linkplain FindKeySeq} always tests all possible keys, class
* FindKeySeq2 stops as soon as it finds the correct key.
*
* @author Alan Kaminsky
* @version 18-Nov-2009
*/
public class FindKeySeq2
{
// Prevent construction.
private FindKeySeq2()
{
}
// Shared variables.
// Command line arguments.
static byte[] plaintext;
static byte[] ciphertext;
static byte[] partialkey;
static int n;
// Variables for doing trial encryptions.
static long keylsbs;
static long maxcounter;
static byte[] foundkey;
static byte[] trialkey;
static byte[] trialciphertext;
static AES256Cipher cipher;
// Main program.
/**
* AES partial key search main program.
*/
public static void main
(String[] args)
throws Exception
{
// Start timing.
long t1 = System.currentTimeMillis();
Comm.init (args);
// Parse command line arguments.
if (args.length != 4) usage();
plaintext = Hex.toByteArray (args[0]);
ciphertext = Hex.toByteArray (args[1]);
partialkey = Hex.toByteArray (args[2]);
n = Integer.parseInt (args[3]);
// Make sure n is not too small or too large.
if (n < 0)
{
System.err.println ("n = " + n + " is too small");
System.exit (1);
}
if (n > 63)
{
System.err.println ("n = " + n + " is too large");
System.exit (1);
}
// Set up variables for doing trial encryptions.
keylsbs =
((partialkey[24] & 0xFFL) << 56) |
((partialkey[25] & 0xFFL) << 48) |
((partialkey[26] & 0xFFL) << 40) |
((partialkey[27] & 0xFFL) << 32) |
((partialkey[28] & 0xFFL) << 24) |
((partialkey[29] & 0xFFL) << 16) |
((partialkey[30] & 0xFFL) << 8) |
((partialkey[31] & 0xFFL) );
maxcounter = (1L << n) - 1L;
foundkey = new byte [32];
trialkey = new byte [32];
System.arraycopy (partialkey, 0, trialkey, 0, 32);
trialciphertext = new byte [16];
cipher = new AES256Cipher (trialkey);
// Try every possible combination of low-order key bits.
for (long counter = 0; counter <= maxcounter; ++ counter)
{
// Fill in low-order key bits.
long lsbs = keylsbs | counter;
trialkey[24] = (byte) (lsbs >>> 56);
trialkey[25] = (byte) (lsbs >>> 48);
trialkey[26] = (byte) (lsbs >>> 40);
trialkey[27] = (byte) (lsbs >>> 32);
trialkey[28] = (byte) (lsbs >>> 24);
trialkey[29] = (byte) (lsbs >>> 16);
trialkey[30] = (byte) (lsbs >>> 8);
trialkey[31] = (byte) (lsbs );
// Try the key.
cipher.setKey (trialkey);
cipher.encrypt (plaintext, trialciphertext);
// If the result equals the ciphertext, we found the key.
if (match (ciphertext, trialciphertext))
{
System.arraycopy (trialkey, 0, foundkey, 0, 32);
break;
}
}
// Stop timing.
long t2 = System.currentTimeMillis();
// Print the key we found.
System.out.println (Hex.toString (foundkey));
System.out.println ((t2-t1) + " msec");
}
// Hidden operations.
/**
* Returns true if the two byte arrays match.
*/
private static boolean match
(byte[] a,
byte[] b)
{
boolean matchsofar = true;
int n = a.length;
for (int i = 0; i < n; ++ i)
{
matchsofar = matchsofar && a[i] == b[i];
}
return matchsofar;
}
/**
* Print a usage message and exit.
*/
private static void usage()
{
System.err.println ("Usage: java edu.rit.clu.keysearch.FindKeySeq2 <ciphertext> <partialkey> <n>");
System.err.println ("<plaintext> = Plaintext (128-bit hexadecimal number)");
System.err.println ("<ciphertext> = Ciphertext (128-bit hexadecimal number)");
System.err.println ("<partialkey> = Partial key (256-bit hexadecimal number)");
System.err.println ("<n> = Number of key bits to search for");
System.exit (1);
}
}
</code> </pre>
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