DES.java

packagecom.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.
 */
publicclassDES {

privateStringkey;
privatefinalString[] subKeys;

privatevoidsanitize(Stringkey) {
intlength = key.length();
if (length != 64) {
thrownewIllegalArgumentException("DES key must be supplied as a 64 character binary string");
 }
 }

DES(Stringkey) {
sanitize(key);
this.key = key;
subKeys = getSubkeys(key);
 }

publicStringgetKey() {
returnthis.key;
 }

publicvoidsetKey(Stringkey) {
sanitize(key);
this.key = key;
 }

// Permutation table to convert initial 64-bit key to 56 bit key
privatestaticfinalint[] 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
privatestaticfinalint[] 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
privatestaticfinalint[] 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 permutation of each 64 but message block
privatestaticfinalint[] 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
privatestaticfinalint[] 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
privatestaticfinalint[][] 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}};

privatestaticfinalint[][] 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}};

privatestaticfinalint[][] 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}};

privatestaticfinalint[][] 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}};

privatestaticfinalint[][] 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}};

privatestaticfinalint[][] 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}};

privatestaticfinalint[][] 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}};

privatestaticfinalint[][] 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}};

privatestaticfinalint[][][] S = {S1, S2, S3, S4, S5, S6, S7, S8};

// Permutation table, used in the Feistel function post s-box usage
staticfinalint[] 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
staticfinalint[] IP_INVERSE = {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};

privateString[] getSubkeys(StringoriginalKey) {
StringBuilderpermutedKey = newStringBuilder(); // Initial permutation of keys via pc1
inti;
intj;
for (i = 0; i < 56; i++) {
permutedKey.append(originalKey.charAt(PC1[i] - 1));
 }
String[] subKeys = newString[16];
StringinitialPermutedKey = permutedKey.toString();
Stringc0 = initialPermutedKey.substring(0, 28);
Stringd0 = initialPermutedKey.substring(28);

// We will now operate on the left and right halves of the permutedKey
for (i = 0; i < 16; i++) {
StringcN = c0.substring(KEY_SHIFTS[i]) + c0.substring(0, KEY_SHIFTS[i]);
StringdN = 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++) {
Stringkey = subKeys[i];
permutedKey.setLength(0);
for (j = 0; j < 48; j++) {
permutedKey.append(key.charAt(PC2[j] - 1));
 }
subKeys[i] = permutedKey.toString();
 }

returnsubKeys;
 }

privateStringxOR(Stringa, Stringb) {
inti;
intl = a.length();
StringBuilderxor = newStringBuilder();
for (i = 0; i < l; i++) {
intfirstBit = a.charAt(i) - 48; // 48 is '0' in ascii
intsecondBit = b.charAt(i) - 48;
xor.append((firstBit ^ secondBit));
 }
returnxor.toString();
 }

privateStringcreatePaddedString(Strings, intdesiredLength, charpad) {
inti;
intl = s.length();
StringBuilderpaddedString = newStringBuilder();
intdiff = desiredLength - l;
for (i = 0; i < diff; i++) {
paddedString.append(pad);
 }
returnpaddedString.toString();
 }

privateStringpad(Strings, intdesiredLength) {
returncreatePaddedString(s, desiredLength, '0') + s;
 }

privateStringpadLast(Strings, intdesiredLength) {
returns + createPaddedString(s, desiredLength, '\u0000');
 }

privateStringfeistel(StringmessageBlock, Stringkey) {
inti;
StringBuilderexpandedKey = newStringBuilder();
for (i = 0; i < 48; i++) {
expandedKey.append(messageBlock.charAt(EXPANSION[i] - 1));
 }
StringmixedKey = xOR(expandedKey.toString(), key);
StringBuildersubstitutedString = newStringBuilder();

// 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) {
Stringblock = mixedKey.substring(i, i + 6);
introw = (block.charAt(0) - 48) * 2 + (block.charAt(5) - 48);
intcol = (block.charAt(1) - 48) * 8 + (block.charAt(2) - 48) * 4 + (block.charAt(3) - 48) * 2 + (block.charAt(4) - 48);
StringsubstitutedBlock = pad(Integer.toBinaryString(S[i / 6][row][col]), 4);
substitutedString.append(substitutedBlock);
 }

StringBuilderpermutedString = newStringBuilder();
for (i = 0; i < 32; i++) {
permutedString.append(substitutedString.charAt(PERMUTATION[i] - 1));
 }

returnpermutedString.toString();
 }

privateStringencryptBlock(Stringmessage, String[] keys) {
StringBuilderpermutedMessage = newStringBuilder();
inti;
for (i = 0; i < 64; i++) {
permutedMessage.append(message.charAt(IP[i] - 1));
 }
Stringe0 = permutedMessage.substring(0, 32);
Stringf0 = permutedMessage.substring(32);

// Iterate 16 times
for (i = 0; i < 16; i++) {
StringeN = f0; // Previous Right block
StringfN = xOR(e0, feistel(f0, keys[i]));
e0 = eN;
f0 = fN;
 }

StringcombinedBlock = f0 + e0; // Reverse the 16th block
permutedMessage.setLength(0);
for (i = 0; i < 64; i++) {
permutedMessage.append(combinedBlock.charAt(IP_INVERSE[i] - 1));
 }
returnpermutedMessage.toString();
 }

// To decode, we follow the same process as encoding, but with reversed keys
privateStringdecryptBlock(Stringmessage, String[] keys) {
String[] reversedKeys = newString[keys.length];
for (inti = 0; i < keys.length; i++) {
reversedKeys[i] = keys[keys.length - i - 1];
 }
returnencryptBlock(message, reversedKeys);
 }

/**
 * @param message Message to be encrypted
 * @return The encrypted message, as a binary string
 */
publicStringencrypt(Stringmessage) {
StringBuilderencryptedMessage = newStringBuilder();
intl = message.length();
inti;
intj;
if (l % 8 != 0) {
intdesiredLength = (l / 8 + 1) * 8;
l = desiredLength;
message = padLast(message, desiredLength);
 }

for (i = 0; i < l; i += 8) {
Stringblock = message.substring(i, i + 8);
StringBuilderbitBlock = newStringBuilder();
byte[] bytes = block.getBytes();
for (j = 0; j < 8; j++) {
bitBlock.append(pad(Integer.toBinaryString(bytes[j]), 8));
 }
encryptedMessage.append(encryptBlock(bitBlock.toString(), subKeys));
 }
returnencryptedMessage.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
 */
publicStringdecrypt(Stringmessage) {
StringBuilderdecryptedMessage = newStringBuilder();
intl = message.length();
inti;
intj;
if (l % 64 != 0) {
thrownewIllegalArgumentException("Encrypted message should be a multiple of 64 characters in length");
 }
for (i = 0; i < l; i += 64) {
Stringblock = message.substring(i, i + 64);
Stringresult = decryptBlock(block, subKeys);
byte[] res = newbyte[8];
for (j = 0; j < 64; j += 8) {
res[j / 8] = (byte) Integer.parseInt(result.substring(j, j + 8), 2);
 }
decryptedMessage.append(newString(res));
 }
returndecryptedMessage.toString().replace("\0", ""); // Get rid of the null bytes used for padding
 }
}