Data Encryption Standard (DES) is a block cypher algorithm that takes the plain text in blocks of 64 bits and converts them to ciphertext using keys of 48 bits. It is a symmetric key algorithm, which means that the same key is used for encrypting and decrypting data.
#include "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;
}
 is a block cypher algorithm that takes the plain text in blocks of 64 bits and converts them to ciphertext){kind=link}
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