DES Implementation In 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);
        }
            
    }