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DES Algorithm - Illustrated with Java Programs
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This chapter describes:
- A Java program to illustrate the DES key schedule Algorithm.
- A Java program to illustrate the DES cipher algorithm.
DESSubkeysTest.java - DES Key Schedule Algorithm Illustration
As an illustration to the DES key schedule algorithm described in the
previous chapter, I wrote the following Java program, DESKSubkeysTest.java:
/* DESSubkeysTest.java
* Copyright (c) 2002 by Dr. Herong Yang
*/
class DESSubkeysTest {
public static void main(String[] a) {
try {
byte[] theKey = getTestKey();
byte[][] subKeys = getSubkeys(theKey);
boolean ok = validateSubkeys(subKeys);
System.out.println("DES subkeys test result: "+ok);
} catch (Exception e) {
e.printStackTrace();
}
}
static final int[] PC1 = {
57, 49, 41, 33, 25, 17, 9,
1, 58, 50, 42, 34, 26, 18,
10, 2, 59, 51, 43, 35, 27,
19, 11, 3, 60, 52, 44, 36,
63, 55, 47, 39, 31, 23, 15,
7, 62, 54, 46, 38, 30, 22,
14, 6, 61, 53, 45, 37, 29,
21, 13, 5, 28, 20, 12, 4
};
static final int[] PC2 = {
14, 17, 11, 24, 1, 5,
3, 28, 15, 6, 21, 10,
23, 19, 12, 4, 26, 8,
16, 7, 27, 20, 13, 2,
41, 52, 31, 37, 47, 55,
30, 40, 51, 45, 33, 48,
44, 49, 39, 56, 34, 53,
46, 42, 50, 36, 29, 32
};
static final int[] SHIFTS = {
1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1
};
private static byte[][] getSubkeys(byte[] theKey)
throws Exception {
printBytes(theKey,"Input key");
int activeKeySize = PC1.length;
int numOfSubKeys = SHIFTS.length;
byte[] activeKey = selectBits(theKey,PC1);
printBytes(activeKey,"After permuted choice 1 - Active key");
int halfKeySize = activeKeySize/2;
byte[] c = selectBits(activeKey,0,halfKeySize);
byte[] d = selectBits(activeKey,halfKeySize,halfKeySize);
byte[][] subKeys = new byte[numOfSubKeys][];
for (int k=0; k<numOfSubKeys; k++) {
c = rotateLeft(c,halfKeySize,SHIFTS[k]);
d = rotateLeft(d,halfKeySize,SHIFTS[k]);
byte[] cd = concatenateBits(c,halfKeySize,d,halfKeySize);
printBytes(cd,"Subkey #"+(k+1)+" after shifting");
subKeys[k] = selectBits(cd,PC2);
printBytes(subKeys[k],"Subkey #"+(k+1)
+" after permuted choice 2");
}
return subKeys;
}
private static byte[] rotateLeft(byte[] in, int len, int step) {
int numOfBytes = (len-1)/8 + 1;
byte[] out = new byte[numOfBytes];
for (int i=0; i<len; i++) {
int val = getBit(in,(i+step)%len);
setBit(out,i,val);
}
return out;
}
private static byte[] concatenateBits(byte[] a, int aLen, byte[] b,
int bLen) {
int numOfBytes = (aLen+bLen-1)/8 + 1;
byte[] out = new byte[numOfBytes];
int j = 0;
for (int i=0; i<aLen; i++) {
int val = getBit(a,i);
setBit(out,j,val);
j++;
}
for (int i=0; i<bLen; i++) {
int val = getBit(b,i);
setBit(out,j,val);
j++;
}
return out;
}
private static byte[] selectBits(byte[] in, int pos, int len) {
int numOfBytes = (len-1)/8 + 1;
byte[] out = new byte[numOfBytes];
for (int i=0; i<len; i++) {
int val = getBit(in,pos+i);
setBit(out,i,val);
}
return out;
}
private static byte[] selectBits(byte[] in, int[] map) {
int numOfBytes = (map.length-1)/8 + 1;
byte[] out = new byte[numOfBytes];
for (int i=0; i<map.length; i++) {
int val = getBit(in,map[i]-1);
setBit(out,i,val);
// System.out.println("i="+i+", pos="+(map[i]-1)+", val="+val);
}
return out;
}
private static int getBit(byte[] data, int pos) {
int posByte = pos/8;
int posBit = pos%8;
byte valByte = data[posByte];
int valInt = valByte>>(8-(posBit+1)) & 0x0001;
return valInt;
}
private static void setBit(byte[] data, int pos, int val) {
int posByte = pos/8;
int posBit = pos%8;
byte oldByte = data[posByte];
oldByte = (byte) (((0xFF7F>>posBit) & oldByte) & 0x00FF);
byte newByte = (byte) ((val<<(8-(posBit+1))) | oldByte);
data[posByte] = newByte;
}
(Continued on next part...)
Part:
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