Cryptography Tutorials - Herong's Tutorial Notes
Dr. Herong Yang, Version 4.00

DES Algorithm - Illustrated with Java Programs

Part:   1  2  3  4  5  6 

(Continued from previous part...)

DESCipherTest.java - DES Cipher Algorithm Illustration

As an illustration to the DES cipher algorithm described in the previous chapter, I wrote the following Java program, DESKCipher.java:

/* DESCipherTest.java
 * Copyright (c) 2002 by Dr. Herong Yang
 */
class DESCipherTest {
   public static void main(String[] a) {
      try {
         byte[][] subKeys = getTestSubkeys();
         byte[] theMsg = getTestMsg();
         byte[] theCph = cipherBlock(theMsg,subKeys);
         boolean ok = validateCipher(theCph);
         System.out.println("DES cipher test result: "+ok);
      } catch (Exception e) {
         e.printStackTrace();
         return;
      }
   }
   static final int[] IP = {
      58, 50, 42, 34, 26, 18, 10, 2,
      60, 52, 44, 36, 28, 20, 12, 4,
      62, 54, 46, 38, 30, 22, 14, 6,
      64, 56, 48, 40, 32, 24, 16, 8,
      57, 49, 41, 33, 25, 17,  9, 1,
      59, 51, 43, 35, 27, 19, 11, 3,
      61, 53, 45, 37, 29, 21, 13, 5,
      63, 55, 47, 39, 31, 23, 15, 7
   };
   static final int[] E = {
      32,  1,  2,  3,  4,  5,
       4,  5,  6,  7,  8,  9,
       8,  9, 10, 11, 12, 13,
      12, 13, 14, 15, 16, 17,
      16, 17, 18, 19, 20, 21,
      20, 21, 22, 23, 24, 25,
      24, 25, 26, 27, 28, 29,
      28, 29, 30, 31, 32,  1
   };
   static final int[] P = {
      16,  7, 20, 21,
      29, 12, 28, 17,
       1, 15, 23, 26,
       5, 18, 31, 10,
       2,  8, 24, 14,
      32, 27,  3,  9,
      19, 13, 30,  6,
      22, 11,  4, 25
   };
   static final int[] FP = {
      40, 8, 48, 16, 56, 24, 64, 32,
      39, 7, 47, 15, 55, 23, 63, 31,
      38, 6, 46, 14, 54, 22, 62, 30,
      37, 5, 45, 13, 53, 21, 61, 29,
      36, 4, 44, 12, 52, 20, 60, 28,
      35, 3, 43, 11, 51, 19, 59, 27,
      34, 2, 42, 10, 50, 18, 58, 26,
      33, 1, 41,  9, 49, 17, 57, 25
   };
   private static byte[] cipherBlock(byte[] theMsg, byte[][] subKeys)
      throws Exception {
      if (theMsg.length<8) 
         throw new Exception("Message is less than 64 bits.");
      printBytes(theMsg,"Input message");
      theMsg = selectBits(theMsg,IP); // Initial Permutation
      printBytes(theMsg,"After initial permutation");
      int blockSize = IP.length;
      byte[] l = selectBits(theMsg,0,blockSize/2);
      byte[] r = selectBits(theMsg,blockSize/2,blockSize/2);
      int numOfSubKeys = subKeys.length;
      for (int k=0; k<numOfSubKeys; k++) {
      	 byte[] rBackup = r;
         r = selectBits(r,E); // Expansion
         printBytes(r,"R: After E expansion");
         r = doXORBytes(r,subKeys[k]); // XOR with the sub key
         printBytes(r,"R: After XOR with the subkey");
         r = substitution6x4(r); // Substitution
         printBytes(r,"R: After S boxes");
         r = selectBits(r,P); // Permutation
         printBytes(r,"R: After P permutation");
         r = doXORBytes(l,r); // XOR with the previous left half
         printBytes(r,"Right half at round #"+(k+1));
         l = rBackup; // Taking the previous right half
      }
      byte[] lr = concatenateBits(r,blockSize/2,l,blockSize/2);
      printBytes(lr,"After 16 rounds");
      lr = selectBits(lr,FP); // Inverse Permutation
      printBytes(lr,"After final permutation");
      return lr;
   } 
   private static byte[] doXORBytes(byte[] a, byte[] b) {
      byte[] out = new byte[a.length];
      for (int i=0; i<a.length; i++) {
         out[i] = (byte) (a[i] ^ b[i]);
      }
      return out;
   }
   static final int[] S = {
14,  4, 13,  1,  2, 15, 11,  8,  3, 10,  6, 12,  5,  9,  0,  7, // S1
 0, 15,  7,  4, 14,  2, 13,  1, 10,  6, 12, 11,  9,  5,  3,  8,
 4,  1, 14,  8, 13,  6,  2, 11, 15, 12,  9,  7,  3, 10,  5,  0,
15, 12,  8,  2,  4,  9,  1,  7,  5, 11,  3, 14, 10,  0,  6, 13,
15,  1,  8, 14,  6, 11,  3,  4,  9,  7,  2, 13, 12,  0,  5, 10, // S2
 3, 13,  4,  7, 15,  2,  8, 14, 12,  0,  1, 10,  6,  9, 11,  5,
 0, 14,  7, 11, 10,  4, 13,  1,  5,  8, 12,  6,  9,  3,  2, 15,
13,  8, 10,  1,  3, 15,  4,  2, 11,  6,  7, 12,  0,  5, 14,  9,
10,  0,  9, 14,  6,  3, 15,  5,  1, 13, 12,  7, 11,  4,  2,  8, // S3
13,  7,  0,  9,  3,  4,  6, 10,  2,  8,  5, 14, 12, 11, 15,  1,
13,  6,  4,  9,  8, 15,  3,  0, 11,  1,  2, 12,  5, 10, 14,  7,
 1, 10, 13,  0,  6,  9,  8,  7,  4, 15, 14,  3, 11,  5,  2, 12,
 7, 13, 14,  3,  0,  6,  9, 10,  1,  2,  8,  5, 11, 12,  4, 15, // S4
13,  8, 11,  5,  6, 15,  0,  3,  4,  7,  2, 12,  1, 10, 14,  9,
10,  6,  9,  0, 12, 11,  7, 13, 15,  1,  3, 14,  5,  2,  8,  4,
 3, 15,  0,  6, 10,  1, 13,  8,  9,  4,  5, 11, 12,  7,  2, 14,
 2, 12,  4,  1,  7, 10, 11,  6,  8,  5,  3, 15, 13,  0, 14,  9, // S5
14, 11,  2, 12,  4,  7, 13,  1,  5,  0, 15, 10,  3,  9,  8,  6,
 4,  2,  1, 11, 10, 13,  7,  8, 15,  9, 12,  5,  6,  3,  0, 14,
11,  8, 12,  7,  1, 14,  2, 13,  6, 15,  0,  9, 10,  4,  5,  3,
12,  1, 10, 15,  9,  2,  6,  8,  0, 13,  3,  4, 14,  7,  5, 11, // S6
10, 15,  4,  2,  7, 12,  9,  5,  6,  1, 13, 14,  0, 11,  3,  8,
 9, 14, 15,  5,  2,  8, 12,  3,  7,  0,  4, 10,  1, 13, 11,  6,
 4,  3,  2, 12,  9,  5, 15, 10, 11, 14,  1,  7,  6,  0,  8, 13,
 4, 11,  2, 14, 15,  0,  8, 13,  3, 12,  9,  7,  5, 10,  6,  1, // S7
13,  0, 11,  7,  4,  9,  1, 10, 14,  3,  5, 12,  2, 15,  8,  6,
 1,  4, 11, 13, 12,  3,  7, 14, 10, 15,  6,  8,  0,  5,  9,  2,
 6, 11, 13,  8,  1,  4, 10,  7,  9,  5,  0, 15, 14,  2,  3, 12,
13,  2,  8,  4,  6, 15, 11,  1, 10,  9,  3, 14,  5,  0, 12,  7, // S8
 1, 15, 13,  8, 10,  3,  7,  4, 12,  5,  6, 11,  0, 14,  9,  2,
 7, 11,  4,  1,  9, 12, 14,  2,  0,  6, 10, 13, 15,  3,  5,  8,
 2,  1, 14,  7,  4, 10,  8, 13, 15, 12,  9,  0,  3,  5,  6, 11
   };   

(Continued on next part...)

Part:   1  2  3  4  5  6 

Dr. Herong Yang, updated in 2007
Cryptography Tutorials - Herong's Tutorial Notes - DES Algorithm - Illustrated with Java Programs