crack.c

#define _XOPEN_SOURCE
#include <ctype.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

int yell_args(int argc, char** argv);
short is_password(const char* plain, const char* salt, const char* cipher);
short dict_attack(const char* salt, const char* cipher);

int main(int argc, char *argv[])
{
    if (yell_args(argc, argv))
    {
        return 1;
    }

    char salt[2];
    strncpy(salt, argv[1], 2);

    // do dictionary based attack
    if (!dict_attack(salt, argv[1]))
    {
        puts("Dictionary attack failed:(");
        return 1;
    }

    return 0;
}

int yell_args(int argc, char** argv)
{
    if (argc < 2)
    {
        printf("You passed no arguments!\n");
        return 1;
    }
    else if (argc > 2)
    {
        printf("You passed to much arguments.\n");
        return 1;
    }

    return 0;
}

short is_password(const char* plain, const char* salt, const char* cipher)
{
    return strcmp(crypt(plain, salt), cipher) == 0;
}

short dict_attack(const char* salt, const char* cipher)
{
    FILE* fp = fopen("/usr/share/dict/words", "r");

    char word[256];

    int success = 0;
    char* hacked;

    while(fgets(word, sizeof(word), fp) != NULL)
    {
        int len = strlen(word);

        if (word[len - 1] == '\n')
            word[len - 1] = 0;

        if(is_password(word, salt, cipher))
        {
            hacked = word;
            success = 1;
            break;
        }
    }

    fclose(fp);

    if (success)

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

    return success;
}