Data encryption standard (DES) | Set 1

15 May, 2022
Data encryption standard (DES) has been found vulnerable to very powerful attacks and therefore, the popularity of DES has been found slightly on the decline. DES is a block cipher and encrypts data in blocks of size of 64 bits each, which means 64 bits of plain text go as the input to DES, which produces 64 bits of ciphertext. The same algorithm and key are used for encryption and decryption, with minor differences. The key length is 56 bits. The basic idea is shown in the figure.
We have mentioned that DES uses a 56-bit key. Actually, the initial key consists of 64 bits. However, before the DES process even starts, every 8th bit of the key is discarded to produce a 56-bit key. That is bit positions 8, 16, 24, 32, 40, 48, 56, and 64 are discarded. 
Thus, the discarding of every 8th bit of the key produces a 56-bit key from the original 64-bit key.DES is based on the two fundamental attributes of cryptography: substitution (also called confusion) and transposition (also called diffusion). DES consists of 16 steps, each of which is called a round. Each round performs the steps of substitution and transposition. Let us now discuss the broad-level steps in DES. 
In the first step, the 64-bit plain text block is handed over to an initial Permutation (IP) function.The initial permutation is performed on plain text.Next, the initial permutation (IP) produces two halves of the permuted block; saying Left Plain Text (LPT) and Right Plain Text (RPT).Now each LPT and RPT go through 16 rounds of the encryption process.In the end, LPT and RPT are rejoined and a Final Permutation (FP) is performed on the combined blockThe result of this process produces 64-bit ciphertext.
In the first step, the 64-bit plain text block is handed over to an initial Permutation (IP) function.
The initial permutation is performed on plain text.
Next, the initial permutation (IP) produces two halves of the permuted block; saying Left Plain Text (LPT) and Right Plain Text (RPT).
Now each LPT and RPT go through 16 rounds of the encryption process.
In the end, LPT and RPT are rejoined and a Final Permutation (FP) is performed on the combined block
The result of this process produces 64-bit ciphertext.
Initial Permutation (IP): As we have noted, the initial permutation (IP) happens only once and it happens before the first round. It suggests how the transposition in IP should proceed, as shown in the figure. For example, it says that the IP replaces the first bit of the original plain text block with the 58th bit of the original plain text, the second bit with the 50th bit of the original plain text block, and so on.
This is nothing but jugglery of bit positions of the original plain text block. the same rule applies to all the other bit positions shown in the figure.
As we have noted after IP is done, the resulting 64-bit permuted text block is divided into two half blocks. Each half-block consists of 32 bits, and each of the 16 rounds, in turn, consists of the broad level steps outlined in the figure. 
Step-1: Key transformation: We have noted initial 64-bit key is transformed into a 56-bit key by discarding every 8th bit of the initial key. Thus, for each a 56-bit key is available. From this 56-bit key, a different 48-bit Sub Key is generated during each round using a process called key transformation. For this, the 56-bit key is divided into two halves, each of 28 bits. These halves are circularly shifted left by one or two positions, depending on the round.
For example, if the round numbers 1, 2, 9, or 16 the shift is done by only one position for other rounds, the circular shift is done by two positions. The number of key bits shifted per round is shown in the figure.
After an appropriate shift, 48 of the 56 bits are selected. for selecting 48 of the 56 bits the table is shown in the figure given below. For instance, after the shift, bit number 14 moves to the first position, bit number 17 moves to the second position, and so on. If we observe the table carefully, we will realize that it contains only 48-bit positions. Bit number 18 is discarded (we will not find it in the table), like 7 others, to reduce a 56-bit key to a 48-bit key. Since the key transformation process involves permutation as well as a selection of a 48-bit subset of the original 56-bit key it is called Compression Permutation.
Because of this compression permutation technique, a different subset of key bits is used in each round. That makes DES not easy to crack.
Step-2: Expansion Permutation: Recall that after the initial permutation, we had two 32-bit plain text areas called Left Plain Text(LPT) and Right Plain Text(RPT). During the expansion permutation, the RPT is expanded from 32 bits to 48 bits. Bits are permuted as well hence called expansion permutation. This happens as the 32-bit RPT is divided into 8 blocks, with each block consisting of 4 bits. Then, each 4-bit block of the previous step is then expanded to a corresponding 6-bit block, i.e., per 4-bit block, 2 more bits are added. 
This process results in expansion as well as a permutation of the input bit while creating output. The key transformation process compresses the 56-bit key to 48 bits. Then the expansion permutation process expands the 32-bit RPT to 48-bits. Now the 48-bit key is XOR with 48-bit RPT and the resulting output is given to the next step, which is the S-Box substitution.
C++
Java
Python
#include <bits/stdc++.h>using namespace std;string hex2bin(string s){    // hexadecimal to binary conversion    unordered_map<char, string> mp;    mp['0'] = "0000";    mp['1'] = "0001";    mp['2'] = "0010";    mp['3'] = "0011";    mp['4'] = "0100";    mp['5'] = "0101";    mp['6'] = "0110";    mp['7'] = "0111";    mp['8'] = "1000";    mp['9'] = "1001";    mp['A'] = "1010";    mp['B'] = "1011";    mp['C'] = "1100";    mp['D'] = "1101";    mp['E'] = "1110";    mp['F'] = "1111";    string bin = "";    for (int i = 0; i < s.size(); i++) {        bin += mp[s[i]];    }    return bin;}string bin2hex(string s){    // binary to hexadecimal conversion    unordered_map<string, string> mp;    mp["0000"] = "0";    mp["0001"] = "1";    mp["0010"] = "2";    mp["0011"] = "3";    mp["0100"] = "4";    mp["0101"] = "5";    mp["0110"] = "6";    mp["0111"] = "7";    mp["1000"] = "8";    mp["1001"] = "9";    mp["1010"] = "A";    mp["1011"] = "B";    mp["1100"] = "C";    mp["1101"] = "D";    mp["1110"] = "E";    mp["1111"] = "F";    string hex = "";    for (int i = 0; i < s.length(); i += 4) {        string ch = "";        ch += s[i];        ch += s[i + 1];        ch += s[i + 2];        ch += s[i + 3];        hex += mp[ch];    }    return hex;} string permute(string k, int* arr, int n){    string per = "";    for (int i = 0; i < n; i++) {        per += k[arr[i] - 1];    }    return per;} string shift_left(string k, int shifts){    string s = "";    for (int i = 0; i < shifts; i++) {        for (int j = 1; j < 28; j++) {            s += k[j];        }        s += k[0];        k = s;        s = "";    }    return k;} string xor_(string a, string b){    string ans = "";    for (int i = 0; i < a.size(); i++) {        if (a[i] == b[i]) {            ans += "0";        }        else {            ans += "1";        }    }    return ans;}string encrypt(string pt, vector<string> rkb, vector<string> rk){    // Hexadecimal to binary    pt = hex2bin(pt);     // Initial Permutation Table    int initial_perm[64] = { 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 };    // Initial Permutation    pt = permute(pt, initial_perm, 64);    cout << "After initial permutation: " << bin2hex(pt) << endl;     // Splitting    string left = pt.substr(0, 32);    string right = pt.substr(32, 32);    cout << "After splitting: L0=" << bin2hex(left)         << " R0=" << bin2hex(right) << endl;     // Expansion D-box Table    int exp_d[48] = { 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 };     // S-box Table    int s[8][4][16] = { { 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 },                        { 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 },                         { 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 },                        { 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 },                        { 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 },                        { 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 },                        { 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 },                        { 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 } };     // Straight Permutation Table    int per[32] = { 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 };     cout << endl;    for (int i = 0; i < 16; i++) {        // Expansion D-box        string right_expanded = permute(right, exp_d, 48);         // XOR RoundKey[i] and right_expanded        string x = xor_(rkb[i], right_expanded);         // S-boxes        string op = "";        for (int i = 0; i < 8; i++) {            int row = 2 * int(x[i * 6] - '0') + int(x[i * 6 + 5] - '0');            int col = 8 * int(x[i * 6 + 1] - '0') + 4 * int(x[i * 6 + 2] - '0') + 2 * int(x[i * 6 + 3] - '0') + int(x[i * 6 + 4] - '0');            int val = s[i][row][col];            op += char(val / 8 + '0');            val = val % 8;            op += char(val / 4 + '0');            val = val % 4;            op += char(val / 2 + '0');            val = val % 2;            op += char(val + '0');        }        // Straight D-box        op = permute(op, per, 32);         // XOR left and op        x = xor_(op, left);         left = x;         // Swapper        if (i != 15) {            swap(left, right);        }        cout << "Round " << i + 1 << " " << bin2hex(left) << " "             << bin2hex(right) << " " << rk[i] << endl;    }     // Combination    string combine = left + right;     // Final Permutation Table    int final_perm[64] = { 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 };     // Final Permutation    string cipher = bin2hex(permute(combine, final_perm, 64));    return cipher;}int main(){    // pt is plain text    string pt, key;    /*cout<<"Enter plain text(in hexadecimal): ";    cin>>pt;    cout<<"Enter key(in hexadecimal): ";    cin>>key;*/     pt = "123456ABCD132536";    key = "AABB09182736CCDD";    // Key Generation     // Hex to binary    key = hex2bin(key);     // Parity bit drop table    int keyp[56] = { 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 };     // getting 56 bit key from 64 bit using the parity bits    key = permute(key, keyp, 56); // key without parity     // Number of bit shifts    int shift_table[16] = { 1, 1, 2, 2,                            2, 2, 2, 2,                            1, 2, 2, 2,                            2, 2, 2, 1 };     // Key- Compression Table    int key_comp[48] = { 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 };     // Splitting    string left = key.substr(0, 28);    string right = key.substr(28, 28);     vector<string> rkb; // rkb for RoundKeys in binary    vector<string> rk; // rk for RoundKeys in hexadecimal    for (int i = 0; i < 16; i++) {        // Shifting        left = shift_left(left, shift_table[i]);        right = shift_left(right, shift_table[i]);         // Combining        string combine = left + right;         // Key Compression        string RoundKey = permute(combine, key_comp, 48);         rkb.push_back(RoundKey);        rk.push_back(bin2hex(RoundKey));    }     cout << "\nEncryption:\n\n";    string cipher = encrypt(pt, rkb, rk);    cout << "\nCipher Text: " << cipher << endl;     cout << "\nDecryption\n\n";    reverse(rkb.begin(), rkb.end());    reverse(rk.begin(), rk.end());    string text = encrypt(cipher, rkb, rk);    cout << "\nPlain Text: " << text << endl;}
import java.util.*; class Main {    private static class DES {        // CONSTANTS        // Initial Permutation Table        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 Table        int[] IP1 = { 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 };         // first key-hePermutation Table        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 };         // second key-Permutation Table        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 };         // Expansion D-box Table        int[] EP = { 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 };         // Straight Permutation Table        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-box Table        int[][][] sbox = {            { { 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 } },             { { 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 } },            { { 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 } },            { { 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 } },            { { 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 } },            { { 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 } },            { { 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 } },            { { 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 } }        };        int[] shiftBits = { 1, 1, 2, 2, 2, 2, 2, 2,                            1, 2, 2, 2, 2, 2, 2, 1 };         // hexadecimal to binary conversion        String hextoBin(String input)        {            int n = input.length() * 4;            input = Long.toBinaryString(                Long.parseUnsignedLong(input, 16));            while (input.length() < n)                input = "0" + input;            return input;        }         // binary to hexadecimal conversion        String binToHex(String input)        {            int n = (int)input.length() / 4;            input = Long.toHexString(                Long.parseUnsignedLong(input, 2));            while (input.length() < n)                input = "0" + input;            return input;        }         // per-mutate input hexadecimal        // according to specified sequence        String permutation(int[] sequence, String input)        {            String output = "";            input = hextoBin(input);            for (int i = 0; i < sequence.length; i++)                output += input.charAt(sequence[i] - 1);            output = binToHex(output);            return output;        }         // xor 2 hexadecimal strings        String xor(String a, String b)        {            // hexadecimal to decimal(base 10)            long t_a = Long.parseUnsignedLong(a, 16);            // hexadecimal to decimal(base 10)            long t_b = Long.parseUnsignedLong(b, 16);            // xor            t_a = t_a ^ t_b;            // decimal to hexadecimal            a = Long.toHexString(t_a);            // prepend 0's to maintain length            while (a.length() < b.length())                a = "0" + a;            return a;        }         // left Circular Shifting bits        String leftCircularShift(String input, int numBits)        {            int n = input.length() * 4;            int perm[] = new int[n];            for (int i = 0; i < n - 1; i++)                perm[i] = (i + 2);            perm[n - 1] = 1;            while (numBits-- > 0)                input = permutation(perm, input);            return input;        }         // preparing 16 keys for 16 rounds        String[] getKeys(String key)        {            String keys[] = new String[16];            // first key permutation            key = permutation(PC1, key);            for (int i = 0; i < 16; i++) {                key = leftCircularShift(                          key.substring(0, 7), shiftBits[i])                      + leftCircularShift(key.substring(7, 14),                                          shiftBits[i]);                // second key permutation                keys[i] = permutation(PC2, key);            }            return keys;        }         // s-box lookup        String sBox(String input)        {            String output = "";            input = hextoBin(input);            for (int i = 0; i < 48; i += 6) {                String temp = input.substring(i, i + 6);                int num = i / 6;                int row = Integer.parseInt(                    temp.charAt(0) + "" + temp.charAt(5), 2);                int col = Integer.parseInt(                    temp.substring(1, 5), 2);                output += Integer.toHexString(                    sbox[num][row][col]);            }            return output;        }         String round(String input, String key, int num)        {            // fk            String left = input.substring(0, 8);            String temp = input.substring(8, 16);            String right = temp;            // Expansion permutation            temp = permutation(EP, temp);            // xor temp and round key            temp = xor(temp, key);            // lookup in s-box table            temp = sBox(temp);            // Straight D-box            temp = permutation(P, temp);            // xor            left = xor(left, temp);            System.out.println("Round "                               + (num + 1) + " "                               + right.toUpperCase()                               + " " + left.toUpperCase() + " "                               + key.toUpperCase());             // swapper            return right + left;        }         String encrypt(String plainText, String key)        {            int i;            // get round keys            String keys[] = getKeys(key);             // initial permutation            plainText = permutation(IP, plainText);            System.out.println(                "After initial permutation: "                + plainText.toUpperCase());            System.out.println(                "After splitting: L0="                + plainText.substring(0, 8).toUpperCase()                + " R0="                + plainText.substring(8, 16).toUpperCase() + "\n");             // 16 rounds            for (i = 0; i < 16; i++) {                plainText = round(plainText, keys[i], i);            }             // 32-bit swap            plainText = plainText.substring(8, 16)                        + plainText.substring(0, 8);             // final permutation            plainText = permutation(IP1, plainText);            return plainText;        }         String decrypt(String plainText, String key)        {            int i;            // get round keys            String keys[] = getKeys(key);             // initial permutation            plainText = permutation(IP, plainText);            System.out.println(                "After initial permutation: "                + plainText.toUpperCase());            System.out.println(                "After splitting: L0="                + plainText.substring(0, 8).toUpperCase()                + " R0=" + plainText.substring(8, 16).toUpperCase()                + "\n");             // 16-rounds            for (i = 15; i > -1; i--) {                plainText = round(plainText, keys[i], 15 - i);            }             // 32-bit swap            plainText = plainText.substring(8, 16)                        + plainText.substring(0, 8);            plainText = permutation(IP1, plainText);            return plainText;        }    }    public static void main(String args[])    {        String text = "123456ABCD132536";        String key = "AABB09182736CCDD";         DES cipher = new DES();        System.out.println("Encryption:\n");        text = cipher.encrypt(text, key);        System.out.println(            "\nCipher Text: " + text.toUpperCase() + "\n");        System.out.println("Decryption\n");        text = cipher.decrypt(text, key);        System.out.println(            "\nPlain Text: "            + text.toUpperCase());    }}// code contributed by Abhay Bhat
# Hexadecimal to binary conversiondef hex2bin(s):    mp = {'0' : "0000",          '1' : "0001",          '2' : "0010",          '3' : "0011",          '4' : "0100",          '5' : "0101",          '6' : "0110",          '7' : "0111",          '8' : "1000",          '9' : "1001",          'A' : "1010",          'B' : "1011",          'C' : "1100",          'D' : "1101",          'E' : "1110",          'F' : "1111" }    bin = ""    for i in range(len(s)):        bin = bin + mp[s[i]]    return bin     # Binary to hexadecimal conversiondef bin2hex(s):    mp = {"0000" : '0',          "0001" : '1',          "0010" : '2',          "0011" : '3',          "0100" : '4',          "0101" : '5',          "0110" : '6',          "0111" : '7',          "1000" : '8',          "1001" : '9',          "1010" : 'A',          "1011" : 'B',          "1100" : 'C',          "1101" : 'D',          "1110" : 'E',          "1111" : 'F' }    hex = ""    for i in range(0,len(s),4):        ch = ""        ch = ch + s[i]        ch = ch + s[i + 1]        ch = ch + s[i + 2]        ch = ch + s[i + 3]        hex = hex + mp[ch]             return hex # Binary to decimal conversiondef bin2dec(binary):           binary1 = binary    decimal, i, n = 0, 0, 0    while(binary != 0):        dec = binary % 10        decimal = decimal + dec * pow(2, i)        binary = binary//10        i += 1    return decimal # Decimal to binary conversiondef dec2bin(num):    res = bin(num).replace("0b", "")    if(len(res)%4 != 0):        div = len(res) / 4        div = int(div)        counter =(4 * (div + 1)) - len(res)        for i in range(0, counter):            res = '0' + res    return res # Permute function to rearrange the bitsdef permute(k, arr, n):    permutation = ""    for i in range(0, n):        permutation = permutation + k[arr[i] - 1]    return permutation # shifting the bits towards left by nth shiftsdef shift_left(k, nth_shifts):    s = ""    for i in range(nth_shifts):        for j in range(1,len(k)):            s = s + k[j]        s = s + k[0]        k = s        s = ""    return k    # calculating xow of two strings of binary number a and bdef xor(a, b):    ans = ""    for i in range(len(a)):        if a[i] == b[i]:            ans = ans + "0"        else:            ans = ans + "1"    return ans # Table of Position of 64 bits at initial level: Initial Permutation Tableinitial_perm = [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 D-box Tableexp_d = [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 ] # Straight Permutation Tableper = [ 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-box Tablesbox =  [[[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 ]],                     [[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 ]],            [ [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 ]],                 [ [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] ],                  [ [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 ]],                [ [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] ],                   [ [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] ],                 [ [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] ] ]   # Final Permutation Tablefinal_perm = [ 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 ] def encrypt(pt, rkb, rk):    pt = hex2bin(pt)         # Initial Permutation    pt = permute(pt, initial_perm, 64)    print("After initial permutation", bin2hex(pt))         # Splitting    left = pt[0:32]    right = pt[32:64]    for i in range(0, 16):        #  Expansion D-box: Expanding the 32 bits data into 48 bits        right_expanded = permute(right, exp_d, 48)                 # XOR RoundKey[i] and right_expanded        xor_x = xor(right_expanded, rkb[i])         # S-boxex: substituting the value from s-box table by calculating row and column        sbox_str = ""        for j in range(0, 8):            row = bin2dec(int(xor_x[j * 6] + xor_x[j * 6 + 5]))            col = bin2dec(int(xor_x[j * 6 + 1] + xor_x[j * 6 + 2] + xor_x[j * 6 + 3] + xor_x[j * 6 + 4]))            val = sbox[j][row][col]            sbox_str = sbox_str + dec2bin(val)                     # Straight D-box: After substituting rearranging the bits         sbox_str = permute(sbox_str, per, 32)                 # XOR left and sbox_str        result = xor(left, sbox_str)        left = result                 # Swapper        if(i != 15):            left, right = right, left        print("Round ", i + 1, " ", bin2hex(left), " ", bin2hex(right), " ", rk[i])         # Combination    combine = left + right         # Final permutation: final rearranging of bits to get cipher text    cipher_text = permute(combine, final_perm, 64)    return cipher_text pt = "123456ABCD132536"key = "AABB09182736CCDD" # Key generation# --hex to binarykey = hex2bin(key) # --parity bit drop tablekeyp = [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 ] # getting 56 bit key from 64 bit using the parity bitskey = permute(key, keyp, 56) # Number of bit shiftsshift_table = [1, 1, 2, 2,                2, 2, 2, 2,                1, 2, 2, 2,                2, 2, 2, 1 ] # Key- Compression Table : Compression of key from 56 bits to 48 bitskey_comp = [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 ] # Splittingleft = key[0:28]    # rkb for RoundKeys in binaryright = key[28:56]  # rk for RoundKeys in hexadecimal rkb = []rk  = []for i in range(0, 16):    # Shifting the bits by nth shifts by checking from shift table    left = shift_left(left, shift_table[i])    right = shift_left(right, shift_table[i])         # Combination of left and right string    combine_str = left + right         # Compression of key from 56 to 48 bits    round_key = permute(combine_str, key_comp, 48)      rkb.append(round_key)    rk.append(bin2hex(round_key)) print("Encryption")cipher_text = bin2hex(encrypt(pt, rkb, rk))print("Cipher Text : ",cipher_text) print("Decryption")rkb_rev = rkb[::-1]rk_rev = rk[::-1]text = bin2hex(encrypt(cipher_text, rkb_rev, rk_rev))print("Plain Text : ",text) # This code is contributed by Aditya Jain
Output: 
Encryption:

After initial permutation: 14A7D67818CA18AD
After splitting: L0=14A7D678 R0=18CA18AD

Round 1 18CA18AD 5A78E394 194CD072DE8C
Round 2 5A78E394 4A1210F6 4568581ABCCE
Round 3 4A1210F6 B8089591 06EDA4ACF5B5
Round 4 B8089591 236779C2 DA2D032B6EE3
Round 5 236779C2 A15A4B87 69A629FEC913
Round 6 A15A4B87 2E8F9C65 C1948E87475E
Round 7 2E8F9C65 A9FC20A3 708AD2DDB3C0
Round 8 A9FC20A3 308BEE97 34F822F0C66D
Round 9 308BEE97 10AF9D37 84BB4473DCCC
Round 10 10AF9D37 6CA6CB20 02765708B5BF
Round 11 6CA6CB20 FF3C485F 6D5560AF7CA5
Round 12 FF3C485F 22A5963B C2C1E96A4BF3
Round 13 22A5963B 387CCDAA 99C31397C91F
Round 14 387CCDAA BD2DD2AB 251B8BC717D0
Round 15 BD2DD2AB CF26B472 3330C5D9A36D
Round 16 19BA9212 CF26B472 181C5D75C66D

Cipher Text: C0B7A8D05F3A829C

Decryption

After initial permutation: 19BA9212CF26B472
After splitting: L0=19BA9212 R0=CF26B472

Round 1 CF26B472 BD2DD2AB 181C5D75C66D
Round 2 BD2DD2AB 387CCDAA 3330C5D9A36D
Round 3 387CCDAA 22A5963B 251B8BC717D0
Round 4 22A5963B FF3C485F 99C31397C91F
Round 5 FF3C485F 6CA6CB20 C2C1E96A4BF3
Round 6 6CA6CB20 10AF9D37 6D5560AF7CA5
Round 7 10AF9D37 308BEE97 02765708B5BF
Round 8 308BEE97 A9FC20A3 84BB4473DCCC
Round 9 A9FC20A3 2E8F9C65 34F822F0C66D
Round 10 2E8F9C65 A15A4B87 708AD2DDB3C0
Round 11 A15A4B87 236779C2 C1948E87475E
Round 12 236779C2 B8089591 69A629FEC913
Round 13 B8089591 4A1210F6 DA2D032B6EE3
Round 14 4A1210F6 5A78E394 06EDA4ACF5B5
Round 15 5A78E394 18CA18AD 4568581ABCCE
Round 16 14A7D678 18CA18AD 194CD072DE8C

Plain Text: 123456ABCD132536
Refer: Difference between AES and DES ciphers 
MohitBansal3
AbhayBhat
Bond0071
ImAditya
anikaseth98
adnanirshad158
gabaa406
Pushpender007
23603vaibhav2021
abhishk01
cryptography
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