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DES Algorithm - Illustrated with Java Programs
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(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...)
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