package com.thealgorithms.ciphers; /** * This class is build to demonstrate the application of the DES-algorithm (https://en.wikipedia.org/wiki/Data_Encryption_Standard) on a * plain English message. The supplied key must be in form of a 64 bit binary String. */ public class DES { private String key; private String subKeys[]; private void sanitize(String key) { int length = key.length(); if (length != 64) { throw new IllegalArgumentException("DES key must be supplied as a 64 character binary string"); } } DES(String key) { sanitize(key); this.key = key; subKeys = getSubkeys(key); } public String getKey() { return this.key; } public void setKey(String key) { sanitize(key); this.key = key; } //Permutation table to convert initial 64 bit key to 56 bit key private static 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 }; //Lookup table used to shift the initial key, in order to generate the subkeys private static int[] KEY_SHIFTS = { 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 }; //Table to convert the 56 bit subkeys to 48 bit subkeys private static 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 }; //Initial permutatation of each 64 but message block private static 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 }; //Expansion table to convert right half of message blocks from 32 bits to 48 bits private static int[] expansion = { 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 }; //The eight substitution boxes are defined below private static 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} }; private static 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} }; private static 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} }; private static 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} }; private static 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} }; private static 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} }; private static 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} }; private static 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} }; private static int[][][] s = {s1, s2, s3, s4, s5, s6, s7, s8}; //Permutation table, used in the feistel function post s-box usage static int[] permutation = { 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 }; //Table used for final inversion of the message box after 16 rounds of Feistel Function static int[] IPinverse = { 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 String[] getSubkeys(String originalKey) { StringBuilder permutedKey = new StringBuilder(); //Initial permutation of keys via PC1 int i, j; for (i = 0; i < 56; i++) { permutedKey.append(originalKey.charAt(PC1[i] - 1)); } String subKeys[] = new String[16]; String initialPermutedKey = permutedKey.toString(); String C0 = initialPermutedKey.substring(0, 28), D0 = initialPermutedKey.substring(28); //We will now operate on the left and right halves of the permutedKey for (i = 0; i < 16; i++) { String Cn = C0.substring(KEY_SHIFTS[i]) + C0.substring(0, KEY_SHIFTS[i]); String Dn = D0.substring(KEY_SHIFTS[i]) + D0.substring(0, KEY_SHIFTS[i]); subKeys[i] = Cn + Dn; C0 = Cn; //Re-assign the values to create running permutation D0 = Dn; } //Let us shrink the keys to 48 bits (well, characters here) using PC2 for (i = 0; i < 16; i++) { String key = subKeys[i]; permutedKey.setLength(0); for (j = 0; j < 48; j++) { permutedKey.append(key.charAt(PC2[j] - 1)); } subKeys[i] = permutedKey.toString(); } return subKeys; } private String XOR(String a, String b) { int i, l = a.length(); StringBuilder xor = new StringBuilder(); for (i = 0; i < l; i++) { int firstBit = a.charAt(i) - 48; // 48 is '0' in ascii int secondBit = b.charAt(i) - 48; xor.append((firstBit ^ secondBit)); } return xor.toString(); } private String createPaddedString(String s, int desiredLength, char pad) { int i, l = s.length(); StringBuilder paddedString = new StringBuilder(); int diff = desiredLength - l; for (i = 0; i < diff; i++) { paddedString.append(pad); } return paddedString.toString(); } private String pad(String s, int desiredLength) { return createPaddedString(s, desiredLength, '0') + s; } private String padLast(String s, int desiredLength) { return s + createPaddedString(s, desiredLength, '\u0000'); } private String feistel(String messageBlock, String key) { int i; StringBuilder expandedKey = new StringBuilder(); for (i = 0; i < 48; i++) { expandedKey.append(messageBlock.charAt(expansion[i] - 1)); } String mixedKey = XOR(expandedKey.toString(), key); StringBuilder substitutedString = new StringBuilder(); //Let us now use the s-boxes to transform each 6 bit (length here) block to 4 bits for (i = 0; i < 48; i += 6) { String block = mixedKey.substring(i, i + 6); int row = (block.charAt(0) - 48) * 2 + (block.charAt(5) - 48); int col = (block.charAt(1) - 48) * 8 + (block.charAt(2) - 48) * 4 + (block.charAt(3) - 48) * 2 + (block.charAt(4) - 48); String substitutedBlock = pad(Integer.toBinaryString(s[i / 6][row][col]), 4); substitutedString.append(substitutedBlock); } StringBuilder permutedString = new StringBuilder(); for (i = 0; i < 32; i++) { permutedString.append(substitutedString.charAt(permutation[i] - 1)); } return permutedString.toString(); } private String encryptBlock(String message, String keys[]) { StringBuilder permutedMessage = new StringBuilder(); int i; for (i = 0; i < 64; i++) { permutedMessage.append(message.charAt(IP[i] - 1)); } String L0 = permutedMessage.substring(0, 32), R0 = permutedMessage.substring(32); //Iterate 16 times for (i = 0; i < 16; i++) { String Ln = R0; // Previous Right block String Rn = XOR(L0, feistel(R0, keys[i])); L0 = Ln; R0 = Rn; } String combinedBlock = R0 + L0; //Reverse the 16th block permutedMessage.setLength(0); for (i = 0; i < 64; i++) { permutedMessage.append(combinedBlock.charAt(IPinverse[i] - 1)); } return permutedMessage.toString(); } //To decode, we follow the same process as encoding, but with reversed keys private String decryptBlock(String message, String keys[]) { String reversedKeys[] = new String[keys.length]; for (int i = 0; i < keys.length; i++) { reversedKeys[i] = keys[keys.length - i - 1]; } return encryptBlock(message, reversedKeys); } /** * @param message Message to be encrypted * @return The encrypted message, as a binary string */ public String encrypt(String message) { StringBuilder encryptedMessage = new StringBuilder(); int l = message.length(), i, j; if (l % 8 != 0) { int desiredLength = (l / 8 + 1) * 8; l = desiredLength; message = padLast(message, desiredLength); } for (i = 0; i < l; i+= 8) { String block = message.substring(i, i + 8); StringBuilder bitBlock = new StringBuilder(); byte[] bytes = block.getBytes(); for (j = 0; j < 8; j++) { bitBlock.append(pad(Integer.toBinaryString(bytes[j]), 8)); } encryptedMessage.append(encryptBlock(bitBlock.toString(), subKeys)); } return encryptedMessage.toString(); } /** * @param message The encrypted string. Expects it to be a multiple of 64 bits, in binary format * @return The decrypted String, in plain English */ public String decrypt(String message) { StringBuilder decryptedMessage = new StringBuilder(); int l = message.length(), i, j; if (l % 64 != 0) { throw new IllegalArgumentException("Encrypted message should be a multiple of 64 characters in length"); } for (i = 0; i < l; i+= 64) { String block = message.substring(i, i + 64); String result = decryptBlock(block.toString(), subKeys); byte res[] = new byte[8]; for (j = 0; j < 64; j+=8) { res[j / 8] = (byte)Integer.parseInt(result.substring(j, j + 8), 2); } decryptedMessage.append(new String(res)); } return decryptedMessage.toString().replace("\0", ""); // Get rid of the null bytes used for padding } }