#include <stdio.h>
#include <stdlib.h>
#include <math.h>
// Function to calculate greatest common divisor (GCD)
int gcd(int a, int b) {
if (b == 0)
return a;
return gcd(b, a % b);
}
// Function to generate RSA keys
void generateRSAKeys(int *n, int *e, int *d) {
// Choose two prime numbers (p and q)
int p;
int q;
printf("enter two prime numbers:");
scanf("%d %d",&p,&q);
// Calculate n = p * q
*n = p * q;
// Calculate Euler's totient function (φ(n))
int phi = (p - 1) * (q - 1);
// Choose a public exponent (e) such that 1 < e < φ(n) and gcd(e, φ(n)) = 1
*e = 5; // You can choose a different value for e, typically a prime number
// Calculate the private exponent (d) such that (d * e) % φ(n) = 1
*d = 0;
while ((*d * *e) % phi != 1) {
(*d)++;
}
}
// Function to perform modular exponentiation (base^exponent % modulus)
int modExp(int base, int exponent, int modulus) {
int result = 1;
while (exponent > 0) {
if (exponent % 2 == 1) {
result = (result * base) % modulus;
}
base = (base * base) % modulus;
exponent /= 2;
}
return result;
}
// Function to encrypt a message using the public key
int encrypt(int message, int publicKey, int modulus) {
return modExp(message, publicKey, modulus);
}
// Function to decrypt a message using the private key
int decrypt(int ciphertext, int privateKey, int modulus) {
return modExp(ciphertext, privateKey, modulus);
}
int main() {
int n, e, d;
int plaintext;
printf("enter plaintext:");
scanf("%d",&plaintext);
generateRSAKeys(&n, &e, &d);
printf("Original message: %d\n", plaintext);
int ciphertext = encrypt(plaintext, e, n);
printf("Encrypted message: %d\n", ciphertext);
int decryptedMessage = decrypt(ciphertext, d, n);
printf("Decrypted message: %d\n", decryptedMessage);
return 0;
}

#include <math.h>
#include <stdio.h>
// Power function to return value of a ^ b mod P
long long int power(long long int a, long long int b,
long long int P)
{
if (b == 1)
return a;
else
return (((long long int)pow(a, b)) % P);
}
int main()
{
long long int P, G, x, a, y, b, ka, kb;
// Both the persons will be agreed upon the
// public keys G and P
printf("Enter the value of P:");
scanf("%lld",&P); // A prime number P is taken
printf("The value of P : %lld\n", P);
printf("Enter the value of G:");
scanf("%lld",&G); // A primitive root for P, G is taken
printf("The value of G : %lld\n\n", G);
// Alice will choose the private key a
a = 4; // a is the chosen private key
printf("The private key a for Alice : %lld\n", a);
x = power(G, a, P); // gets the generated key
// Bob will choose the private key b
b = 3; // b is the chosen private key
printf("The private key b for Bob : %lld\n\n", b);
y = power(G, b, P); // gets the generated key
// Generating the secret key after the exchange
// of keys
ka = power(y, a, P); // Secret key for Alice
kb = power(x, b, P); // Secret key for Bob
printf("Secret key for the Alice is : %lld\n", ka);
printf("Secret Key for the Bob is : %lld\n", kb);
return 0;
}

from cryptography.fernet import Fernet
print("Enter the string: ")
message = input()
key = Fernet.generate_key()
fernet = Fernet(key)
encMessage = fernet.encrypt(message.encode())
print("original string: ", message)
print("encrypted string: ", encMessage)

decMessage = fernet.decrypt(encMessage).decode()
 
print("decrypted string: ", decMessage)