-
Notifications
You must be signed in to change notification settings - Fork 1
/
DES.cpp
363 lines (342 loc) · 10.1 KB
/
DES.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
// Libraries
#include <bits/stdc++.h>
using namespace std;
// Array to hold 16 keys Generated by some different key scheduling algo
string round_keys[16];
// String to hold the plain text
string pt;
string str2bin(string s)
{
int n = s.length();
string ans = "";
for (int i = 0; i < n; i++)
{
// convert each char to
// ASCII value
int val = int(s[i]);
// Convert ASCII value to binary
string bin = "";
while (val > 0)
{
(val % 2)? bin.push_back('1') :
bin.push_back('0');
val /= 2;
}
reverse(bin.begin(), bin.end());
while(bin.size()<8){
bin+='0';
}
// cout << bin.size() << s[i] << endl;
ans+=bin;
}
return ans;
}
// Function to convert a number in decimal to binary
string convertDecimalToBinary(int decimal)
{
// binary holding string
string binary;
// main conversion algo
while(decimal != 0) {
binary = (decimal % 2 == 0 ? "0" : "1") + binary;
decimal = decimal/2;
}
// length less than 4 not acceptable
while(binary.length() < 4){
binary = "0" + binary;
}
// returning the string
return binary;
}
// Function to convert a number in binary to decimal
int convertBinaryToDecimal(string binary)
{
// counters
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
// shifting the already divided part of key
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
// shifting the already divided part of key
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;
}
// XOR box
//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 Permutation choice 1 table for converting 64 to 56 bit on key side
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 Permutation choice 2 table for converting 56 to 48 bit on transition from key side to plaintext side
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 Permutation choice 1 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 of 28 bits from above converted string
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 Permutation choice 2 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;
}
}
// Main DES program implementation
string DES(){
// The initial permutation table on plaintext side
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 BOX or E-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
};
// Substitution box with values from 0 to 15 inclusive
// Using Already created S-box
// convert from 48 bit to 32 bits
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 for permuting 32 bits on plaintext side
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
// substr(startindex,len)
string left = perm.substr(0, 32);
string right = perm.substr(32, 32);
// The plain text is encrypted 16 times
// ciphertext holder
string ciphertext ="";
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;
}
// combining both the sides in order to create complete ciphertext
string combined_text = left + right;
ciphertext ="";
// The inverse of the initial permuttaion is applied
for(int i = 0; i < 64; i++){
ciphertext+= combined_text[inverse_permutation[i]-1];
}
// printing out ciphertext after each round
if(i>=10)
cout << " Round " << i << " --> " << ciphertext << endl;
else cout << " Round " << i << " --> " << ciphertext << endl;
}
//And we finally get the cipher text
return ciphertext;
}
int main(){
// A 64 bit key
string key =str2bin("HIHACKER");
cout << "Key Used HIHACKER" << endl;
cout << "Key in 64 bit " << key << endl << endl;
// A block of plain text of 64 bits
pt = str2bin("SAFEZONE");
cout << "Plain Text Used SAFEZOND" << endl << endl;
// Calling the function to generate 16 keys
generate_keys(key);
cout<<" Plain text: "<<pt<<endl;
// Algo
string ct= DES();
cout<<"Final Ciphertext: "<<ct<<endl;
int i = 15;
int j = 0;
while(i > j)
{
string temp = round_keys[i];
round_keys[i] = round_keys[j];
round_keys[j] = temp;
i--;
j++;
}
pt = ct;
string decrypted = DES();
cout << decrypted;
}