Implement the DES algorithm in C++.

 DES algorithm in C++.

#include <iostream>

#include <string>

using namespace std;

// Array to hold the 16 keys

string round_keys[16];

string shift_left_once(string key_chunk){ 

    string shifted="";  

        for(int i = 1; i < 28; i++){ 

            shifted += key_chunk[i]; 

        } 

        shifted += key_chunk[0];   

    return shifted; 

} 

string shift_left_twice(string key_chunk){ 

    string shifted=""; 

    for(int i = 0; i < 2; i++){ 

        for(int j = 1; j < 28; j++){ 

            shifted += key_chunk[j]; 

        } 

        shifted += key_chunk[0]; 

        key_chunk= shifted; 

        shifted =""; 

    } 

    return key_chunk; 

}

void generate_keys(string key){

// The PC1 table 

int pc1[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 

};

// The PC2 table

int pc2[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 

}; 

string perm_key =""; 

for(int i = 0; i < 56; i++){ 

perm_key+= key[pc1[i]-1]; 

} 

string left= perm_key.substr(0, 28); 

string right= perm_key.substr(28, 28); 

// Generating 16 keys

for(int i=0; i<16; i++){ 

if(i == 0 || i == 1 || i==8 || i==15 ){

left= shift_left_once(left); 

right= shift_left_once(right);

} 

else{

left= shift_left_twice(left); 

right= shift_left_twice(right);

}

string combined_key = left + right;

string round_key = ""; 

for(int i = 0; i < 48; i++){ 

round_key += combined_key[pc2[i]-1]; 

}   

round_keys[i] = round_key;

cout<<"Key "<<i+1<<": "<<round_keys[i]<<endl; 

} 

}

int main(){  

string key = "10101010101110110000100100011000001001110011";

  generate_keys(key);

} 

OUTPUT

Key 1: 0000!010011001�100000110001011110010

Key 2: 0100101100000�!00000011011110110010

Key 3: 0000�10101101010010010100111010110101

Key 4: 1110�00010!0000011010110110110001

Key 5: 010�00110!011000101001111010011000101

Key 6: 11000000010!001�101001101001010110

Key 7: !11000100101010100011010111001100000

Key 8: 00010!111�000000101100000110010110

Key 9: !000100101101000100100110110011010

Key 10: 00000101101!00010�1000101010010111

Key 11: 010110100!0011100010101011111000101

Key 12: 1001011000001!�0100101101000001111011

Key 13: �001101!0001100000110101111000010011

Key 14: 0010000110�!100011100011000111000

Key 15: 001001001�00010010!1110101001010110

Key 16: 001!00000011001011100111100010010111