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#include <iostream>
#include <math.h>
#include <stdlib.h>
#include <string.h>
using namespace std;
long int gcd(long int a, long int b) {
if (a == 0)
return b;
if (b == 0)
return a;
return gcd(b, a % b);
}
long int isprime(long int a) {
int i;
for (i = 2; i < a; i++) {
if ((a % i) == 0)
return 0;
}
return 1;
}
long int encrypt(char ch, long int n, long int e) {
int i;
long int temp = ch;
for (i = 1; i < e; i++)
temp = (temp * ch) % n;
return temp;
}
char decrypt(long int ch, long int n, long int d) {
int i;
long int temp = ch;
for (i = 1; i < d; i++)
ch = (temp * ch) % n;
return ch;
}
int main() {
long int i, len;
long int p, q, n, phi, e, d, cipher[50];
char text[50];
cout << "Enter the text to be encrypted: ";
cin.getline(text, sizeof(text));
len = strlen(text);
do {
p = rand() % 800;
} while (!isprime(p));
do {
q = rand() % 800;
} while (!isprime(q));
n = p * q;
phi = (p - 1) * (q - 1);
do {
e = rand() % phi;
} while (gcd(phi, e) != 1);
do {
d = rand() % phi;
} while (((d * e) % phi) != 1);
cout << "Two prime numbers (p and q) are: " << p << " and " << q << endl;
cout << "n(p * q) = " << p << " * " << q << " = " << p * q << endl;
cout << "(p - 1) * (q - 1) = " << phi << endl;
cout << "Public key (n, e): (" << n << ", " << e << ")\n";
cout << "Private key (n, d): (" << n << ", " << d << ")\n";
for (i = 0; i < len; i++)
cipher[i] = encrypt(text[i], n, e);
cout << "Encrypted message: ";
for (i = 0; i < len; i++)
cout << cipher[i];
for (i = 0; i < len; i++)
text[i] = decrypt(cipher[i], n, d);
cout << endl;
cout << "Decrypted message: ";
for (i = 0; i < len; i++)
cout << text[i];
cout << endl;
return 0;
}
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