// Including dependancies
#include <iostream>
#include <string>
#include <cmath>
using namespace std;
// Array to hold 16 keys
string round_keys[16];
// String to hold the plain text
string pt;
// Function to convert a number in decimal to binary
string convertDecimalToBinary(int decimal)
{
string binary;
while(decimal != 0) {
binary = (decimal % 2 == 0 ? "0" : "1") + binary;
decimal = decimal/2;
}
while(binary.length() < 4){
binary = "0" + binary;
}
return binary;
}
// Function to convert a number in binary to decimal
int convertBinaryToDecimal(string binary)
{
int decimal = 0;
int counter = 0;
int size = binary.length();
for(int i = size-1; i >= 0; i--)
{
if(binary[i] == '1'){
decimal += pow(2, counter);
}
counter++;
}
return decimal;
}
// Function to do a circular left shift by 1
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;
}
// Function to do a circular left shift by 2
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;
}
// Function to compute xor between two strings
string Xor(string a, string b){
string result = "";
int size = b.size();
for(int i = 0; i < size; i++){
if(a[i] != b[i]){
result += "1";
}
else{
result += "0";
}
}
return result;
}
// Function to generate the 16 keys.
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
};
// 1. Compressing the key using the PC1 table
string perm_key ="";
for(int i = 0; i < 56; i++){
perm_key+= key[pc1[i]-1];
}
// 2. Dividing the key into two equal halves
string left= perm_key.substr(0, 28);
string right= perm_key.substr(28, 28);
for(int i=0; i<16; i++){
// 3.1. For rounds 1, 2, 9, 16 the key_chunks
// are shifted by one.
if(i == 0 || i == 1 || i==8 || i==15 ){
left= shift_left_once(left);
right= shift_left_once(right);
}
// 3.2. For other rounds, the key_chunks
// are shifted by two
else{
left= shift_left_twice(left);
right= shift_left_twice(right);
}
// Combining the two chunks
string combined_key = left + right;
string round_key = "";
// Finally, using the PC2 table to transpose the key bits
for(int i = 0; i < 48; i++){
round_key += combined_key[pc2[i]-1];
}
round_keys[i] = round_key;
}
}
// Implementing the algorithm
string DES(){
// The initial permutation table
int initial_permutation[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
};
// The expansion table
int expansion_table[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
};
// The substitution boxes. The should contain values
// from 0 to 15 in any order.
int substition_boxes[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
}};
// The permutation table
int permutation_tab[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
};
// The inverse permutation table
int inverse_permutation[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
};
//1. Applying the initial permutation
string perm = "";
for(int i = 0; i < 64; i++){
perm += pt[initial_permutation[i]-1];
}
// 2. Dividing the result into two equal halves
string left = perm.substr(0, 32);
string right = perm.substr(32, 32);
// The plain text is encrypted 16 times
for(int i=0; i<16; i++) {
string right_expanded = "";
// 3.1. The right half of the plain text is expanded
for(int i = 0; i < 48; i++) {
right_expanded += right[expansion_table[i]-1];
}; // 3.3. The result is xored with a key
string xored = Xor(round_keys[i], right_expanded);
string res = "";
// 3.4. The result is divided into 8 equal parts and passed
// through 8 substitution boxes. After passing through a
// substituion box, each box is reduces from 6 to 4 bits.
for(int i=0;i<8; i++){
// Finding row and column indices to lookup the
// substituition box
string row1= xored.substr(i*6,1) + xored.substr(i*6 + 5,1);
int row = convertBinaryToDecimal(row1);
string col1 = xored.substr(i*6 + 1,1) + xored.substr(i*6 + 2,1) + xored.substr(i*6 + 3,1) + xored.substr(i*6 + 4,1);;
int col = convertBinaryToDecimal(col1);
int val = substition_boxes[i][row][col];
res += convertDecimalToBinary(val);
}
// 3.5. Another permutation is applied
string perm2 ="";
for(int i = 0; i < 32; i++){
perm2 += res[permutation_tab[i]-1];
}
// 3.6. The result is xored with the left half
xored = Xor(perm2, left);
// 3.7. The left and the right parts of the plain text are swapped
left = xored;
if(i < 15){
string temp = right;
right = xored;
left = temp;
}
}
// 4. The halves of the plain text are applied
string combined_text = left + right;
string ciphertext ="";
// The inverse of the initial permuttaion is applied
for(int i = 0; i < 64; i++){
ciphertext+= combined_text[inverse_permutation[i]-1];
}
//And we finally get the cipher text
return ciphertext;
}
int main(){
// A 64 bit key
string key= "1010101010";
// A block of plain text of 64 bits
pt= "helloworld";
// Calling the function to generate 16 keys
generate_keys(key);
cout<<
"Plain text: "<<pt<<endl;
// Applying the algo
string ct= DES();
cout<<"Ciphertext: "<<ct<<endl;
}
// 1001111000100110100111110101101011111010010011011011101101110000
// 0100111000111101101000111101100001100101010010011101101011110110
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