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DES Algorithm - Java Implementation

Part:   1  2  3  4 

This tutorial help you to understand:

• A simple Java implementation of the DES cipher algorithm.
• Multiple test cases of DES encryption and decryption.

CipherDES.java - A Simple Java Implementation of DES

Merging the illustration programs from the previous chapter together, I got the following simple Java implementation of the DES algorithm, CipherDES.java:

/* CipherDES.java
 * Copyright (c) 2002 by Dr. Herong Yang, http://www.herongyang.com/
 */
package herong;
import java.io.*;
public class CipherDES {
   public static void main(String[] a) {
      if (a.length<4) {
         System.out.println("Usage:");
         System.out.println("java DesCipher encrypt/decrypt keyFile"
            +" msgFile cphFile");
         return;
      }
      String mode = a[0];
      String keyFile = a[1];
      String msgFile = a[2];
      String cphFile = a[3];
      try {
         byte[] theKey = readBytes(keyFile);
         byte[][] subKeys = getSubkeys(theKey);
         byte[] theMsg = readBytes(msgFile);
         byte[] theCph = cipher(theMsg,subKeys,mode);
         writeBytes(theCph,cphFile);
         printBytes(theKey,"Key block");
         printBytes(theMsg,"Input block");    
         printBytes(theCph,"Output block");    
      } 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[] INVP = {
      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
   };
   public static byte[] cipher(byte[] theMsg, byte[][] subKeys, 
      String mode) throws Exception {
      if (theMsg.length<8) 
         throw new Exception("Message is less than 64 bits.");
      theMsg = selectBits(theMsg,IP); // 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
         if (mode.equalsIgnoreCase("encrypt")) 
            r = doXORBytes(r,subKeys[k]); // XOR with the sub key
         else 
            r = doXORBytes(r,subKeys[numOfSubKeys-k-1]);
         r = substitution6x4(r); // Substitution
         r = selectBits(r,P); // Permutation
         r = doXORBytes(l,r); // XOR with the previous left half
         l = rBackup; // Taking the previous right half
      }
      byte[] lr = concatenateBits(r,blockSize/2,l,blockSize/2);
      lr = selectBits(lr,INVP); // Inverse Permutation
      return lr;
   } 

(Continued on next part...)

Part:   1  2  3  4