## Friday, June 20, 2014

### DES Implementation In Java

DES.java

public class DES {
/* Initial Permutation */
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
};
/* Inverse Initial Permutation */
static final int[] IIP = {
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
};
/* Expansion Permutation */
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
};
/* Permutation Function */
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
};
/* S-Boxes*/
static final int[] S1 = {
14,  4, 13,  1,  2, 15, 11,  8,  3, 10,  6, 12,  5,  9,  0,  7,
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
};
static final int[] S2 = {
15,  1,  8, 14,  6, 11,  3,  4,  9,  7,  2, 13, 12,  0,  5, 10,
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
};
static final int[] S3 = {
10,  0,  9, 14,  6,  3, 15,  5,  1, 13, 12,  7, 11,  4,  2,  8,
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
};
static final int[] S4 = {
7, 13, 14,  3,  0,  6,  9, 10,  1,  2,  8,  5, 11, 12,  4, 15,
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
};
static final int[] S5 = {
2, 12,  4,  1,  7, 10, 11,  6,  8,  5,  3, 15, 13,  0, 14,  9,
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
};
static final int[] S6 = {
12,  1, 10, 15,  9,  2,  6,  8,  0, 13,  3,  4, 14,  7,  5, 11,
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
};
static final int[] S7 = {
4, 11,  2, 14, 15,  0,  8, 13,  3, 12,  9,  7,  5, 10,  6,  1,
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
};
static final int[] S8 = {
13,  2,  8,  4,  6, 15, 11,  1, 10,  9,  3, 14,  5,  0, 12,  7,
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
};
/* Permuted Choice One */
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
};
/* Permuted Choice Two */
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
};
/* Schedule of Left Shifts */
static final int[] SHIFTS = {
1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1
};

public DES() {
}

private byte[] performXOR(byte[] one, byte[] two) {
byte[] result = new byte[one.length];
for (int i = 0 ; i < one.length ; i++) {
result[i] = (byte) (one[i] ^ two[i]);
}
return result;
}

private byte[] permute(byte[] input, int[] mapping) {
int byteCount = 1 + (mapping.length - 1) / 8;
byte[] output = new byte[byteCount];
int pos;

for (int i = 0 ; i < mapping.length ; i++) {
pos = mapping[i] - 1;
int value = getBitFromArray(input, pos);
setBitInArray(output, i, value);
}
return output;
}

private int getBitFromArray(byte[] array, int pos) {
int value;
int bytePos = pos / 8;
int bitPos = pos % 8;
value = (array[bytePos] >> (8 - (bitPos + 1))) & 0x0001;
/* eg: right shift selected byte 5 times to get 3rd bit
* (bitPos = 2) at rightmost position and
* then AND with 0x0001*/
return value;
}

private void setBitInArray(byte[] input, int pos, int value) {
int bytePos = pos / 8;
int bitPos = pos % 8;
byte old = input[bytePos];
old = (byte) (((0xFF7F >> bitPos) & old) & 0x00FF);
byte newByte = (byte) ((value << (8 - (bitPos + 1))) | old);
input[bytePos] = newByte;
}

private byte[] hexStringToByteArray(String string) {
int length = string.length();
int n = (int)Math.ceil((length + 1) / 2);
byte[] result = new byte[n];
for (int i = length - 1; i >= 0 ; i -= 2) {
if (i == 0) {
result[i / 2] = (byte) ((Character.digit('0', 16) << 4)
+ Character.digit(string.charAt(i), 16));
} else {
result[i / 2] = (byte) ((Character.digit(string.charAt(i - 1), 16) << 4)
+ Character.digit(string.charAt(i), 16));
}
}
return result;
}

private void printBytes(byte[] input) {
for (int i = 0 ; i < input.length; i++) {
System.out.print(byteToBits(input[i]) + " ");
}
System.out.println();
}

private String byteToBits(byte b) {
StringBuffer buffer = new StringBuffer();
for (int i = 0 ; i < 8 ; i++)
buffer.append((int)(b >> (8-(i+1)) & 0x0001));
return buffer.toString();
}

private byte[] getBits(byte[] input, int startPos, int length) {
int noOfBytes = (length-1)/8 + 1;
byte[] output = new byte[noOfBytes];
for (int i = 0 ; i < length ; i++) {
int value = getBitFromArray(input, startPos + i);
setBitInArray(output, i, value);
}
return output;
}

private byte[] rotateLeft(byte[] input, int step, int length) {
int noOfBytes = (length - 1) / 8 + 1;
byte[] output = new byte[noOfBytes];
for (int i = 0 ; i < length ; i++) {
int value = getBitFromArray(input, (i + step) % length);
setBitInArray(output, i, value);
}
return output;
}

private byte[] concatBits(byte[] one, int oneLength,
byte[] two, int twoLength) {
int noOfBytes = (oneLength + twoLength - 1) / 8 + 1;
byte[] output = new byte[noOfBytes];
int i = 0, j = 0;
for (; i < oneLength ; i++) {
int value = getBitFromArray(one, i);
setBitInArray(output, j, value);
j++;
}
for (i = 0 ; i < twoLength ; i++) {
int value = getBitFromArray(two, i);
setBitInArray(output, j, value);
j++;
}
return output;
}

private byte[][] getSubKeys(byte[] masterKey) {
int noOfSubKeys = SHIFTS.length;
int keySize = PC1.length;
byte[] key = permute(masterKey, PC1);
byte[][] subKeys = new byte[noOfSubKeys][keySize];
byte[] leftHalf = getBits(key, 0, keySize/2);
byte[] rightHalf = getBits(key, keySize/2, keySize/2);
for (int i = 0 ; i < noOfSubKeys ; i++) {
leftHalf = rotateLeft(leftHalf, SHIFTS[i], keySize/2);
rightHalf = rotateLeft(rightHalf, SHIFTS[i], keySize/2);
byte[] subKey = concatBits(leftHalf, keySize/2, rightHalf, keySize/2);
subKeys[i] = permute(subKey, PC2);
}
return subKeys;
}

public byte[] crypt(byte[] message, byte[] key, String operation) {
if (message.length < 8) {
System.out.println("Message should be atleast 64 bits");
System.exit(1);
}
if (key.length != 8) {
System.out.println("Key should be 64 bits");
System.exit(1);
}
int length = message.length;
int n = (length + 7)/8 * 8;
byte[] cipher = new byte[n];
if (length == 8) {
return cryptText(message, key, operation);
}
int i = 0;
int k = 0;
while (i < length) {
byte[] block = new byte[8];
byte[] result = new byte[8];
int j = 0;
for (; j < 8 && i < length; j++, i++) {
block[j] = message[i];
}
while (j < 8) {
block[j++] = 0x00;
}
System.out.println("BLOCK: ");
printBytes(block);
result = cryptText(block, key, operation);
System.out.println("RESULT: ");
printBytes(result);
for (j = 0 ; j < 8 && k < cipher.length; j++, k++) {
cipher[k] = result[j];
}
}
return cipher;
}

public byte[] cryptText(byte[] message, byte[] key, String operation) {
if (message.length != 8) {
System.out.println("Message should be 64 bits");
System.exit(1);
}
if (key.length != 8) {
System.out.println("Key should be 64 bits");
System.exit(1);
}
byte[] result = null;
int blockSize = IP.length;
byte[][] subKeys = getSubKeys(key);
int noOfRounds = subKeys.length;
/**
* Initial Permutation
*/
message = permute(message, IP);
/**
* Split message into two halves
*/
byte[] leftHalf = getBits(message, 0, blockSize/2);
byte[] rightHalf = getBits(message, blockSize/2, blockSize/2);
for (int i = 0 ; i < noOfRounds ; i++) {
byte[] temp = rightHalf;
/**
* Expansion
*/
rightHalf = permute(rightHalf, E);
/**
* XOR rightHalf with roundKey
*/
byte[] roundKey = null;
if (operation.equalsIgnoreCase("encrypt")) {
roundKey = subKeys[i];
} else if (operation.equalsIgnoreCase("decrypt")) {
roundKey = subKeys[noOfRounds - i - 1];
} else {
System.out.println("Unsupported operation");
System.exit(0);
}
rightHalf = performXOR(rightHalf, roundKey);
/**
* S-Box
*/
rightHalf = sBox(rightHalf);
/**
* Permutation
*/
rightHalf = permute(rightHalf, P);
/**
* XOR rightHalf with leftHalf
*/
rightHalf = performXOR(rightHalf, leftHalf);
/**
* L(i) = R(i-1)
*/
leftHalf = temp;
}
/**
* 32 bit swap
*/
byte[] concatHalves = concatBits(rightHalf, blockSize/2, leftHalf, blockSize/2);
/**
* Inverse Initial Permutation
*/
result = permute(concatHalves, IIP);
return result;
}

private byte[] sBox(byte[] input) {
/**
* Split input to 6-bit blocks
*/
input = split(input,6);
byte[] output = new byte[input.length/2];
int leftHalf = 0;
for (int i = 0; i < input.length ; i++) {
byte block = input[i];
/**
* row - first and last bits
* column - 4 bits in the middle
*/
int row = 2 * (block >> 7 & 0x0001) + (block >> 2 & 0x0001);
int col = block >> 3 & 0x000F;
int[] selectedSBox = getSBox(i);
int rightHalf = selectedSBox[16 * row + col];
if (i % 2 == 0) {
leftHalf = rightHalf;
} else {
output[i/2] = (byte) (16 * leftHalf + rightHalf);
leftHalf = 0;
}
}
return output;
}

private int[] getSBox(int i) {
switch (i) {
case 0: return S1;
case 1: return S2;
case 2: return S3;
case 3: return S4;
case 4: return S5;
case 5: return S6;
case 6: return S7;
case 7: return S8;
default: return null;
}
}

private byte[] split(byte[] input, int length) {
int noOfBytes = (8 * input.length - 1) / length + 1;
byte[] output = new byte[noOfBytes];
for (int i = 0 ; i < noOfBytes ; i++) {
for (int j = 0; j < length ; j++) {
int value = getBitFromArray(input, length * i + j);
setBitInArray(output, 8 * i + j, value);
}
}
return output;
}

public static void main(String[] args) {
DES des = new DES();
byte[] message = des.hexStringToByteArray("123456789ABCDEF");
System.out.println("PLAIN TEXT:");
des.printBytes(message);
byte[] key =  des.hexStringToByteArray("133457799BBCDFF1");
System.out.println("KEY:");
des.printBytes(key);
byte[] cipher = des.crypt(message, key, "encrypt");
System.out.println("CIPHER TEXT:");
des.printBytes(cipher);
byte[] result = des.crypt(cipher, key, "decrypt");
System.out.println("DECRYPTED TEXT:");
des.printBytes(result);
}

}

Output
PLAIN TEXT:
00000001 00100011 01000101 01100111 10001001 10101011 11001101 11101111
KEY:
00010011 00110100 01010111 01111001 10011011 10111100 11011111 11110001
CIPHER TEXT:
10000101 11101000 00010011 01010100 00001111 00001010 10110100 00000101
DECRYPTED TEXT:
00000001 00100011 01000101 01100111 10001001 10101011 11001101 11101111