Code:
#include iostream
#include math.h
#include string.h
#include stdlib.h
using namespace std;
long int p, q, n, t, flag, e[100], d[100], temp[100], j, m[100], en[100], i;
char msg[100];
int prime(long int);
void ce();
long int cd(long int);
void encrypt();
void decrypt();
int prime(long int pr)
{
int i;
j = sqrt(pr);
for (i = 2; i <= j; i++)
{
if (pr % i == 0)
return 0;
}
return 1;
}
int main()
{
cout << "\nENTER FIRST PRIME NUMBER\n";
cin >> p;
flag = prime(p);
if (flag == 0)
{
cout << "\nWRONG INPUT\n";
exit(1);
}
cout << "\nENTER ANOTHER PRIME NUMBER\n";
cin >> q;
flag = prime(q);
if (flag == 0 || p == q)
{
cout << "\nWRONG INPUT\n";
exit(1);
}
cout << "\nENTER MESSAGE\n";
fflush(stdin);
cin >> msg;
for (i = 0; msg[i] != NULL; i++)
m[i] = msg[i];
n = p * q;
t = (p - 1) * (q - 1);
ce();
cout << "\nPOSSIBLE VALUES OF e AND d ARE\n";
for (i = 0; i < j - 1; i++)
cout << e[i] << "\t" << d[i] << "\n";
encrypt();
decrypt();
return 0;
}
void ce()
{
int k;
k = 0;
for (i = 2; i < t; i++)
{
if (t % i == 0)
continue;
flag = prime(i);
if (flag == 1 && i != p && i != q)
{
e[k] = i;
flag = cd(e[k]);
if (flag > 0)
{
d[k] = flag;
k++;
}
if (k == 99)
break;
}
}
}
long int cd(long int x)
{
long int k = 1;
while (1)
{
k = k + t;
if (k % x == 0)
return (k / x);
}
}
void encrypt()
{
long int pt, ct, key = e[0], k, len;
i = 0;
len = strlen(msg);
while (i != len)
{
pt = m[i];
pt = pt - 96;
k = 1;
for (j = 0; j < key; j++)
{
k = k * pt;
k = k % n;
}
temp[i] = k;
ct = k + 96;
en[i] = ct;
i++;
}
en[i] = -1;
cout << "\nTHE ENCRYPTED MESSAGE IS\n";
for (i = 0; en[i] != -1; i++)
printf("%c", en[i]);
}
void decrypt()
{
long int pt, ct, key = d[0], k;
i = 0;
while (en[i] != -1)
{
ct = temp[i];
k = 1;
for (j = 0; j < key; j++)
{
k = k * ct;
k = k % n;
}
pt = k + 96;
m[i] = pt;
i++;
}
m[i] = -1;
cout << "\nTHE DECRYPTED MESSAGE IS\n";
for (i = 0; m[i] != -1; i++)
printf("%c", m[i]);
}
Output:
ENTER FIRST PRIME NUMBER
47
ENTER ANOTHER PRIME NUMBER
53
ENTER MESSAGE
Dharmendra
POSSIBLE VALUES OF e AND d ARE
3 1595
5 957
7 1367
11 435
17 985
19 1259
29 165
31 463
37 1293
41 2217
43 1947
59 1419
61 549
67 2035
71 1415
73 1409
79 1847
83 2075
89 2177
97 1233
101 1421
103 2183
THE ENCRYPTED MESSAGE IS
x`a???]??a
THE DECRYPTED MESSAGE IS
Dharmendra
------------------
(program exited with code: 0)
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