diffie_server.c

// Server side C/C++ program to demonstrate Socket programming
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#define PORT 8080

int ModPow(int x, int y, int p)
{
    int res = 1;
    x = x % p;
    while (y > 0)
    {
    if ((y & 1) == 1){
        res = (res*x) % p;
        // std::cout << res <<" = " <<(res*x) <<  " mod(" << p << ")\n";
    }
    y = y>>1;
    x = (x*x) % p;
    }
    return res;
}

int main(int argc, char const *argv[])
{
    int server_fd, new_socket, valread;
    long long int P = 353, pr = 3, Xa, Xb, Ya, Yb, K1, K2;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[1024] = {0};
    char *hello = "Hello from server";
    printf("Enter value for Xa: ");
    scanf("%lld", &Xa);
    
    Ya = ModPow(pr, Xa, P);
    // Creating socket file descriptor
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0)
    {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }
      
    // Forcefully attaching socket to the port 8080
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,
                                                  &opt, sizeof(opt)))
    {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons( PORT );
      
    // Forcefully attaching socket to the port 8080
    if (bind(server_fd, (struct sockaddr *)&address, 
                                 sizeof(address))<0)
    {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
    if (listen(server_fd, 3) < 0)
    {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address, 
                       (socklen_t*)&addrlen))<0)
    {
        perror("accept");
        exit(EXIT_FAILURE);
    }
    valread = read( new_socket , buffer, 1024);
    printf("%lld\n",buffer );
    send(new_socket , hello , strlen(hello) , 0 );
    printf("Hello message sent\n");
    return 0;
}