ciphertext.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <poll.h>
int main(int argc,char **argv)
{
    struct sockaddr_in server;
    int s;
    char packet[40];
    char response[40];
    struct pollfd p;
    int j;
    if (!argv[1]) return 100;
    if (!inet_aton(argv[1],&server.sin_addr)) return 100;
    server.sin_family = AF_INET;
    server.sin_port = htons(10000);
    while ((s = socket(AF_INET,SOCK_DGRAM,0)) == -1) sleep(1);
    while (connect(s,(struct sockaddr *) &server,sizeof server
    ) == -1) sleep(1);

    for (;;) {
        for (j = 0;j < sizeof packet;++j) packet[j] = random();
        send(s,packet,sizeof packet,0);
        p.fd = s;
        p.events = POLLIN;
        if (poll(&p,1,100) <= 0) continue;
        while (p.revents & POLLIN) {
            if (recv(s,response,sizeof response,0) == sizeof response) {
                if (!memcmp(packet,response,16)) {
                    for (j = 0;j < 16;++j)
                    printf("%02x ",255 & (unsigned int) response[j + 16]);
                    printf("\n");
                    return 0;
                }
            }
            if (poll(&p,1,0) <= 0) break;
        }
    }
}