#include <sys/types.h>

#include <sys/socket.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <sys/wait.h>

#include <signal.h>

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

long int p =13,q =17,n,t,flag,e[1000],d[1000],temp[1000],j,en[1000],m[1000],i;

char buff[1000];

int prime(long int);

void ce();

long int cd(long int);

void encrypt();

void decrypt();

void sig_chld(int signo)

{

pid_t pid;

int stat;

while((pid = waitpid(-1, &stat, WNOHANG))>0)

printf("child %d terminated\n", pid);

return;

}

int main()

{

int listen_sock, conn_sock;

int server_len, client_len;

struct sockaddr_in server_address;

struct sockaddr_in client_address;

listen_sock = socket(AF_INET, SOCK_STREAM, 0);

if (listen_sock == -1)

{

printf("khong tao duoc socket\n");

return 0;

}

printf("Tao socket thanh cong\n");

server_address.sin_family = AF_INET;

inet_aton("127.0.0.1",&server_address.sin_addr);

server_address.sin_port = htons(5500);

server_len = sizeof(server_address);

if(bind(listen_sock, (struct sockaddr *)&server_address,server_len)<0)

{

printf("bind failed.\n");

return 0;

}

printf("bind done\n");

int check = listen(listen_sock,10);

if (check == -1)

{

printf("error connect");

return 0;

}

printf("waiting connect ...\n");

while(1) {

client_len = sizeof(client_address);

conn_sock = accept(listen_sock,(struct sockaddr *)&client_address, &client_len);

if(conn_sock==-1){

printf("error connect\n");

return 1;

}else{

printf("Accept new connection\n");

}

if(fork() == 0){

close(listen_sock);

int sentBytes,revedBytes,i;

//char buff[1024];

int chose;

while(1){

revedBytes = recv(conn_sock,buff,1024,0);

if(revedBytes < 0) break;

if(strcmp(buff,"S")==0) chose = 1;

else if(strcmp(buff,"M")==0) chose =2;

else if(strcmp(buff,"exit")==0) chose = 3;

switch(chose){

case 1:

printf("Menu1 \n");

while(1){

revedBytes = recv(conn_sock,buff,1024,0);

buff[revedBytes]='\0';

if(strcmp(buff,"Q")==0) break;

printf("string send by client : %s\n",buff);

for(i=0;buff[i]!=NULL;i++)

m[i]=buff[i];

n=p*q;

t=(p-1)*(q-1);

ce();

encrypt();

//decrypt();

for (i = 0; i < strlen(buff); i++)

{

buff[i]=en[i];

}

sentBytes=send(conn_sock,buff,1024,0);

}

printf("exit menu1 \n");

break;

case 2:

printf("\n Menu2");

while(1){

revedBytes = recv(conn_sock,buff,1024,0);

buff[revedBytes]='\0';

if(strcmp(buff,"Q")==0) break;

printf("string send by client : %s\n",buff);

n=p*q;

t=(p-1)*(q-1);

for(i=0;buff[i]!=NULL;i++)

en[i]=buff[i] ;

ce();decrypt();

for (i = 0; m[i]!=-1; i++)

{

buff[i]=(char)m[i];

}

buff[i]='\0';

printf("%s\n",buff);

sentBytes=send(conn_sock,buff,1024,0);

}

printf("exit menu2 \n");

break;

case 3:

close(conn_sock);

break;

default:

break;

}

}

close(conn_sock);

exit(1);

}

signal(SIGCHLD,sig_chld);

}

return 1;

}

int prime(long int pr)

{

int i;

j=sqrt(pr);

for(i=2;i<=j;i++)

{

if(pr%i==0)

return 0;

}

return 1;

}

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(buff);

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;

printf("\nTHE ENCRYPTED MESSAGE IS\n");

printf("%s\n",en );

for(i=0;en[i]!=NULL;i++)

printf("%c",en[i]);

}

void decrypt()

{

long int pt,ct,key=d[0],k;

i=0;

while(en[i]!=0)

{

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;

printf("\nTHE DECRYPTED MESSAGE IS\n");

for(i=0;m[i]!=NULL;i++)

printf("%c",m[i]);

}