brute.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <crypt.h>
#include <sys/time.h>

int guesses = 0;

char *
brute(char *dict, int dictlen, char hash[13], int len) {
    unsigned char indeces[len];
    char guess[len + 1];
    int cur;
    char *res;

    memset(indeces, 0, len);
    cur = 0;
    guess[len] = 0;
    while (cur >= 0) {
        if (cur == len) {
            res = crypt(guess, hash);
            guesses++;
            if (!memcmp(res, hash, 13)) {
                res = malloc(len + 1);
                memcpy(res, guess, len + 1);
                return res;
            }
            cur--;
        } else if (indeces[cur] == dictlen + 1) {
            cur--;
        } else {
            guess[cur] = dict[indeces[cur]];
            indeces[cur]++;
            cur++;
            indeces[cur] = 0;
        }
    }
    return NULL;
}

char dict[] = "abcdefghijklmnopqrstuvwxyz";

int
main() {
    char *res;
    char *pass;
    char hash[13];
    char *salt;
    struct timeval start, finish;

    printf("Password: ");
    scanf("%ms", &pass);
    printf("Salt: ");
    scanf("%ms", &salt);

    res = crypt(pass, salt);
    memcpy(hash, res, 13);
    printf("Hash is %s\n", res);

    res = brute(dict, sizeof(dict) - 1, hash, strlen(pass));
    if (res) {
        printf("Found: %s\n", res);
    } else {
        printf("Not found\n");
    }
    free(pass);
    free(salt);
    free(res);
    return 0;
}