Wednesday, July 30, 2014

DES Implementation In Java with ECB | CBC | OFB | CFB Modes Of Operation

Note that these are ONLY basic level programs for easy understanding of the Data Encryption Standard (DES) algorithm

Key Generation - DESkeygen.java
 
import java.io.File;
import java.io.FileWriter;

public class DESkeygen {
 
 private final File file = new File("DESkey.txt");
 private final int KEY_LENGTH = 16;
 private final static char[] hexArray = "0123456789ABCDEF".toCharArray();
 
 public DESkeygen() {
  try {   
   FileWriter fileWriter = new FileWriter(file);
   fileWriter.write("");
   for (int i = 0 ; i < KEY_LENGTH ; i++) {
    double random = Math.random();
    int index = (int) (random * 16);
    fileWriter.append(hexArray[index]);
    fileWriter.flush();
   }
   fileWriter.close();
   System.out.println("Key generated and saved in " + file.getName());
  } catch(Exception exp) {
   exp.printStackTrace();
  }
 }
 
 public static void main(String[] args) {
  new DESkeygen();
 }

}

Encryption - DESencrypt.java
 
import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.Arrays;


public class DESencrypt {
 
 private String mode = null;
 final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();
 
 /* 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 DESencrypt() {
  this.mode = "ECB";
 }
 
 public DESencrypt(String mode) {
  this.mode = mode;
 }
 
 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;
 }
 
 public static String bytesToHex(byte[] bytes) {
     char[] hexChars = new char[bytes.length * 2];
     for ( int j = 0; j < bytes.length; j++ ) {
         int v = bytes[j] & 0xFF;
         hexChars[j * 2] = hexArray[v >>> 4];
         hexChars[j * 2 + 1] = hexArray[v & 0x0F];
     }
     return new String(hexChars);
 }
 
 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) {
   if (mode.equals("ECB")) {
    return cryptText(message, key, operation);
   } else if (mode.equals("CBC")) {
    byte[] iv = getInitializationVector();
    message = XORBytes(message, iv);
    return cryptText(message, key, operation);
   } else if (mode.equals("OFB")) {
    byte[] nounce = getNounce();
    byte[] temp = cryptText(nounce, key, operation);
    byte[] result = XORBytes(temp, message);
    return result;
   } else if (mode.equals("CFB")) {
    
   } else {
    System.out.println("Unsupported mode of operation!");
    return null;
   }   
  }
  int i = 0;
  int k = 0;
  byte[] feedback = new byte[8];  
  if (mode.equals("CBC")) {
   feedback = getInitializationVector();
  } else if (mode.equals("OFB")) {
   feedback = getNounce();   
  } else if (mode.equals("CFB")) {
   feedback = getInitializationVectorCFB();
  }
  
  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) {
    /* pad with white spaces */
    block[j++] = 0x20;
   }
      
   //System.out.println("BLOCK: ");
   //printBytes(block);  
   if (mode.equals("ECB")) {
    result = cryptText(block, key, operation);
   } else if (mode.equals("CBC")) {
    if (operation.equals("encrypt")) {
     block = XORBytes(block, feedback);
     result = cryptText(block, key, operation);
     feedback = Arrays.copyOfRange(result, 0, 8);
    } else if (operation.equals("decrypt")) {
     result = cryptText(block, key, operation);
     result = XORBytes(result, feedback);
     feedback = Arrays.copyOfRange(block, 0, 8);
    }    
   } else if (mode.equals("OFB")) {
    result = cryptText(feedback, key, operation);
    feedback = Arrays.copyOfRange(result, 0, 8);
    result = XORBytes(result, block);    
   } else if (mode.equals("CFB")) {
    if (operation.equals("encrypt")) {
     result = cryptText(feedback, key, operation);
     byte[] resultPart = Arrays.copyOfRange(result, 0, 4);
     byte[] blockPart = Arrays.copyOfRange(block, 0, 4);
     byte[] temp1 = XORBytes(resultPart, blockPart);
     feedback = mergeBytes(Arrays.copyOfRange(result, 4, 8), temp1);     
     resultPart = Arrays.copyOfRange(result, 4, 8);
     blockPart = Arrays.copyOfRange(block, 4, 8);
     result = cryptText(feedback, key, operation);
     byte[] temp2 = XORBytes(resultPart, blockPart);
     feedback = mergeBytes(Arrays.copyOfRange(result, 4, 8), temp2);
     result = mergeBytes(temp1, temp2);
    } else if (operation.equals("decrypt")) {
     result = cryptText(feedback, key, "encrypt");
     byte[] resultPart = Arrays.copyOfRange(result, 0, 4);
     byte[] blockPart = Arrays.copyOfRange(block, 0, 4);
     byte[] temp1 = XORBytes(resultPart, blockPart);
     feedback = mergeBytes(Arrays.copyOfRange(result, 4, 8), blockPart);     
     resultPart = Arrays.copyOfRange(result, 4, 8);
     blockPart = Arrays.copyOfRange(block, 4, 8);
     result = cryptText(feedback, key, "encrypt");
     byte[] temp2 = XORBytes(resultPart, blockPart);
     feedback = mergeBytes(Arrays.copyOfRange(result, 4, 8), blockPart);
     result = mergeBytes(temp1, temp2);
    }    
   } else {
    System.out.println("Unsupported mode of operation!");
    return null;
   }   
   //System.out.println("RESULT: ");
   //printBytes(result);
   for (j = 0 ; j < 8 && k < cipher.length; j++, k++) {
    cipher[k] = result[j];
   }
  }
  return cipher;  
 }
 
 private byte[] getInitializationVector() {
  return hexStringToByteArray("DCBE6AE7EA5D5C61");   
 }
 
 private byte[] getInitializationVectorCFB() {
  return hexStringToByteArray("A5D5C61EFADB4351");   
 }
 
 private byte[] getNounce() {
//  char[] hexArray = "0123456789ABCDEF".toCharArray();
//  String nounceStr = "";
//  for (int i = 0 ; i < 16 ; i++) {
//   double random = Math.random();
//   int index = (int) (random * 16);
//   nounceStr += hexArray[index];   
//  }
//  return hexStringToByteArray(nounceStr);
  return hexStringToByteArray("DCBE6AE7EA5D5C61");
 } 

 private byte[] mergeBytes(byte[] in1, byte[] in2) {
  byte[] out = new byte[in1.length + in2.length];
  int i = 0;
  for (int j = 0 ; j < in1.length ; j++) {
   out[i++] = in1[j];
  }
  for (int j = 0 ; j < in2.length ; j++) {
   out[i++] = in2[j];
  }
  return out;
 }
 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;
 }
 
 public static byte[] XORBytes(byte[] in1, byte[] in2) {  
  byte[] out = new byte[in1.length];
  for (int i = 0 ; i < in1.length ; i++) {
   out[i] = (byte)((in1[i] ^ in2[i]) & 0xff);
  }
  return out;
 }
 
 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) {
  try {
   if (args.length != 1) {
    System.out.println("Usage: java < classname > < mode >"
      + "\n\t< mode > := (ECB|CBC|OFB|CFB)");
    return;
   }
   /* ECB, CBC, OFB, or CFB */   
   String mode = args[0];
   mode = mode.toUpperCase();
   DESencrypt des = new DESencrypt(mode); 
   File keyFile = new File("DESkey.txt");
   File textFile = new File("DESplaintext.txt");
   File cipherFile = new File("DESciphertext.txt");   
   FileReader keyFileReader = new FileReader(keyFile);
   BufferedReader bufferedReader = new BufferedReader(keyFileReader);
   FileInputStream textFileInputStream = new FileInputStream(textFile);
   FileOutputStream cipherFileOutputStream = new FileOutputStream(cipherFile);
   byte[] key = new byte[(int) keyFile.length()];
   String keyString = bufferedReader.readLine();
   key = des.hexStringToByteArray(keyString);
   byte[] message = new byte[(int) textFile.length()];
   textFileInputStream.read(message);        
   byte[] cipher = des.crypt(message, key, "encrypt");   
   cipherFileOutputStream.write(cipher);
   cipherFileOutputStream.flush();
   cipherFileOutputStream.close();
   bufferedReader.close();
   textFileInputStream.close();
   System.out.println("Encryption done! Please check DESciphertext.txt for output!");
  } catch(Exception exp) {
   exp.printStackTrace();
  }
 }
  
}

Decryption - DESdecrypt.java
 
import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.Arrays;


public class DESdecrypt {
 
 private String mode = null;
 final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();
 
 /* 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 DESdecrypt() {
  this.mode = "ECB";
 }
 
 public DESdecrypt(String mode) {
  this.mode = mode;
 }
 
 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;
 }
 
 public static String bytesToHex(byte[] bytes) {
     char[] hexChars = new char[bytes.length * 2];
     for ( int j = 0; j < bytes.length; j++ ) {
         int v = bytes[j] & 0xFF;
         hexChars[j * 2] = hexArray[v >>> 4];
         hexChars[j * 2 + 1] = hexArray[v & 0x0F];
     }
     return new String(hexChars);
 }
 
 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) {
   if (mode.equals("ECB")) {
    return cryptText(message, key, operation);
   } else if (mode.equals("CBC")) {
    byte[] iv = getInitializationVector();
    message = XORBytes(message, iv);
    return cryptText(message, key, operation);
   } else if (mode.equals("OFB")) {    
    byte[] nounce = getNounce();
    byte[] temp = cryptText(nounce, key, "encrypt");
    byte[] result = XORBytes(temp, message);
    return result;
   } else if (mode.equals("CFB")) {
    
   } else {
    System.out.println("Unsupported mode of operation!");
    return null;
   }   
  }
  int i = 0;
  int k = 0;
  byte[] feedback = new byte[8];  
  if (mode.equals("CBC")) {
   feedback = getInitializationVector();
  } else if (mode.equals("OFB")) {
   feedback = getNounce();   
  } else if (mode.equals("CFB")) {
   feedback = getInitializationVectorCFB();
  }
  
  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) {
    /* pad with white spaces */
    block[j++] = 0x20;
   }
      
   //System.out.println("BLOCK: ");
   //printBytes(block);  
   if (mode.equals("ECB")) {
    result = cryptText(block, key, operation);
   } else if (mode.equals("CBC")) {
    if (operation.equals("encrypt")) {
     block = XORBytes(block, feedback);
     result = cryptText(block, key, operation);
     feedback = Arrays.copyOfRange(result, 0, 8);
    } else if (operation.equals("decrypt")) {
     result = cryptText(block, key, operation);
     result = XORBytes(result, feedback);
     feedback = Arrays.copyOfRange(block, 0, 8);
    }    
   } else if (mode.equals("OFB")) {
    result = cryptText(feedback, key, "encrypt");
    feedback = Arrays.copyOfRange(result, 0, 8);
    result = XORBytes(result, block);    
   } else if (mode.equals("CFB")) {
    if (operation.equals("encrypt")) {
     result = cryptText(feedback, key, operation);
     byte[] resultPart = Arrays.copyOfRange(result, 0, 4);
     byte[] blockPart = Arrays.copyOfRange(block, 0, 4);
     byte[] temp1 = XORBytes(resultPart, blockPart);
     feedback = mergeBytes(Arrays.copyOfRange(result, 4, 8), temp1);     
     resultPart = Arrays.copyOfRange(result, 4, 8);
     blockPart = Arrays.copyOfRange(block, 4, 8);
     result = cryptText(feedback, key, operation);
     byte[] temp2 = XORBytes(resultPart, blockPart);
     feedback = mergeBytes(Arrays.copyOfRange(result, 4, 8), temp2);
     result = mergeBytes(temp1, temp2);
    } else if (operation.equals("decrypt")) {
     result = cryptText(feedback, key, "encrypt");
     byte[] resultPart = Arrays.copyOfRange(result, 0, 4);
     byte[] blockPart = Arrays.copyOfRange(block, 0, 4);
     byte[] temp1 = XORBytes(resultPart, blockPart);
     feedback = mergeBytes(Arrays.copyOfRange(result, 4, 8), blockPart);     
     resultPart = Arrays.copyOfRange(result, 4, 8);
     blockPart = Arrays.copyOfRange(block, 4, 8);
     result = cryptText(feedback, key, "encrypt");
     byte[] temp2 = XORBytes(resultPart, blockPart);
     feedback = mergeBytes(Arrays.copyOfRange(result, 4, 8), blockPart);
     result = mergeBytes(temp1, temp2);
    }    
   } else {
    System.out.println("Unsupported mode of operation!");
    return null;
   }   
   //System.out.println("RESULT: ");
   //printBytes(result);
   for (j = 0 ; j < 8 && k < cipher.length; j++, k++) {
    cipher[k] = result[j];
   }
  }
  return cipher;  
 }
 
 private byte[] getInitializationVector() {
  return hexStringToByteArray("DCBE6AE7EA5D5C61");   
 }
 
 private byte[] getInitializationVectorCFB() {
  return hexStringToByteArray("A5D5C61EFADB4351");   
 }
 
 private byte[] getNounce() {
//  char[] hexArray = "0123456789ABCDEF".toCharArray();
//  String nounceStr = "";
//  for (int i = 0 ; i < 16 ; i++) {
//   double random = Math.random();
//   int index = (int) (random * 16);
//   nounceStr += hexArray[index];   
//  }
//  return hexStringToByteArray(nounceStr);
  return hexStringToByteArray("DCBE6AE7EA5D5C61");
 } 

 private byte[] mergeBytes(byte[] in1, byte[] in2) {
  byte[] out = new byte[in1.length + in2.length];
  int i = 0;
  for (int j = 0 ; j < in1.length ; j++) {
   out[i++] = in1[j];
  }
  for (int j = 0 ; j < in2.length ; j++) {
   out[i++] = in2[j];
  }
  return out;
 }
 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;
 }
 
 public static byte[] XORBytes(byte[] in1, byte[] in2) {  
  byte[] out = new byte[in1.length];
  for (int i = 0 ; i < in1.length ; i++) {
   out[i] = (byte)((in1[i] ^ in2[i]) & 0xff);
  }
  return out;
 }
 
 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) {
  try {
   if (args.length != 1) {
    System.out.println("Usage: java < classname > < mode >"
      + "\n\t< mode > := (ECB|CBC|OFB|CFB)");
    return;
   }
   /* ECB, CBC, OFB, or CFB */
   String mode = args[0];
   mode = mode.toUpperCase();
   DESdecrypt des = new DESdecrypt(mode); 
   File keyFile = new File("DESkey.txt");
   File textFile = new File("DESplaintext.txt");
   File cipherFile = new File("DESciphertext.txt");   
   FileReader keyFileReader = new FileReader(keyFile);
   BufferedReader bufferedReader = new BufferedReader(keyFileReader);
   FileInputStream cipherFileInputStream = new FileInputStream(cipherFile);
   FileOutputStream textFileOutputStream = new FileOutputStream(textFile);
   byte[] key = new byte[(int) keyFile.length()];
   String keyString = bufferedReader.readLine();
   key = des.hexStringToByteArray(keyString);
   byte[] cipher = new byte[(int) cipherFile.length()];
   cipherFileInputStream.read(cipher);        
   byte[] message = des.crypt(cipher, key, "decrypt");   
   textFileOutputStream.write(message);
   textFileOutputStream.flush();
   textFileOutputStream.close();
   bufferedReader.close();
   cipherFileInputStream.close();
   System.out.println("Decryption done! Please check DESplaintext.txt for output!");
  } catch(Exception exp) {
   exp.printStackTrace();
  }
 }
  
}

Output
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESkeygen
Key generated and saved in DESkey.txt
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESencrypt
Usage: java <classname> <mode>
<mode> := (ECB|CBC|OFB|CFB)
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESencrypt ecb
Encryption done! Please check DESciphertext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESdecrypt ecb
Decryption done! Please check DESplaintext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESencrypt cbc
Encryption done! Please check DESciphertext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESdecrypt cbc
Decryption done! Please check DESplaintext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESencrypt ofb
Encryption done! Please check DESciphertext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESdecrypt ofb
Decryption done! Please check DESplaintext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESencrypt cfb
Encryption done! Please check DESciphertext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESdecrypt cfb
Decryption done! Please check DESplaintext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace$ java DESdecrypt cfb
Decryption done! Please check DESplaintext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace$ 

About Input/Output Files
DESkeygen.java - (output) DESkey.txt 

DESencrypt.java - (input) DESkey.txt & DESplaintext.txt (output) DESciphertext.txt 
DESdecrypt.java - (input) DESkey.txt & DESciphertext.txt (output) DESplaintext.txt

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The Insane Techie - Android App

Launched an android app for the blog on 07th June 2016. Get it from google play store... Tips for using the app Use in landscape mo...