Vortex Level 18

#include <stdlib.h>
/*
 * vortex18 challenge
 *
 * written by Tim Newsham
 * contributions by Joshua J. Drake
 */
#include <stdio.h>

#define RANDLEN 16
#define BUFLEN 20
#define TERMINATE1 'n'
#define TERMINATE2 's'
#define TERMINATE3 '$'
#define TERMINATE4 'S'

void seedrand(char *seed) {
        char buf[RANDLEN];
        int fd, i;

        /* read in a seed */
        fd = open("/dev/urandom", 0);
        if(fd == -1) exit(1);
        if(read(fd, buf, sizeof buf) != sizeof buf) exit(2);
        close(fd);

        /* make sure it doesnt use the terminator */
        for(i = 0; i < RANDLEN - 1; i++) {
                if(buf[i] == TERMINATE1 || buf[i] == TERMINATE2 || buf[i] == TERMINATE3 || buf[i] == TERMINATE4 || buf[i] == '\0')
                        buf[i] = ' ';
        }
        buf[i] = 0;

        /* return it */
        strcpy(seed, buf);
}

int guess(char *seed) {
        char buf[BUFLEN];
        int i;

        for(i = 0; i < BUFLEN - 1; i++) {
                if(read(0, buf + i, 1) != 1) exit(1);
                if(buf[i] == TERMINATE1 || buf[i] == TERMINATE2 || buf[i] == TERMINATE3 || buf[i] == TERMINATE4)
                        break;
        }
        buf[i] = 0;

        if(strcmp(buf, seed) == 0) return 1;

        printf(buf);
        printf("\n");
        fflush(stdout);

        return 0;
}

int main(int argc, char **argv) {
        char seed[RANDLEN];
        int i;

        seedrand(seed);
        for(i = 0; i < 10; i++) {
                if(guess(seed)) {
                        i = geteuid();
                        setresuid(i, i, i);
                        write(1, "YAY!\n", 5);
                        execlp("/bin/sh", "sh", 0);
                        exit(0);
                }
        }
        printf("sorry.\n");
        return 0;
}