Notes

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

#define MAX_MSG 100
int main()
{ int sid,n;
double c;
char line[MAX_MSG];
struct sockaddr_in server_address;
int server_addlen;
server_address.sin_family=AF_INET;
server_address.sin_addr.s_addr=inet_addr("127.0.0.1");
server_address.sin_port=5080;
server_addlen=sizeof(server_address);
sid=socket(AF_INET,SOCK_STREAM,0);
connect(sid,(struct sockaddr *)&server_address,server_addlen);

do{
printf("Enter your message : ");
scanf("%s", line);

send(sid, line, strlen(line) + 1, 0);
printf("Message sent to server: (%s)n", line);
//printf("Enter 2nd number : ");
//scanf("%s", line);
//send(sid, line, strlen(line) + 1, 0);
//printf("data sent (%s)n", line);
n=0;
n=recv(sid, line, MAX_MSG, 0);
printf("Encrypted message received from server %sn", line);

double p = 3;
double q = 7;

// First part of public key:
double x = p*q;

// Finding other part of public key.
// e stands for encrypt
double e = 2;
double phi = (p-1)*(q-1);
while (e < phi)
{
// e must be co-prime to phi and
// smaller than phi.
if (gcd(e, phi)==1)
break;
else
e++;
}

// Private key (d stands for decrypt)
// choosing d such that it satisfies
// d*e = 1 + k * totient
int k = 2; // A constant value
double d = (1 + (k*phi))/e;
c=atoi(line);

// Decryption m = (c ^ d) % n//client side
double m = pow(c, d);
m = fmod(m, x);
printf("nOriginal Message Decrypted = %lf", m);
}while(strcmp(line, "quit"));


printf("closing connection with the servern");
close(sid);
return(0);
}