Brute Force Password Cracker

password_cracker.c

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <string.h>

#define PASSWORD_TO_CRACK "vK6b"

// Increment the lowest digit by 1, check if it passed the last character in the char set
int incrementPass(char* password, int maxChar, int currLength) {
	++password[0];
	// Check if any of digits are full
	int i = 0;

	while(i < currLength && password[i] >= maxChar) {
		password[i] = 0;

		if(i < currLength - 1) ++password[++i];
		else return 0;
	}

	return 1;
}

// Convert count string to readable characters in the character set
void convertPassword(char* password, const char* table, char* iteration, int length) {
	int i;

	for(i = 0; i < length; ++i) iteration[i] = table[ password[i] ];

	iteration[length + 1] = '\0';
}

// Check if current iteration matches the real password
int tryThePassword(char* iteration, char* realPW, unsigned int* counter, unsigned int* billion) {
	if(strcmp(iteration, realPW) == 0) {
		printf("\nFOUND %s at try #%d%d\n", iteration, *billion, *counter);
		return 1;
	} else if(++(*counter) % 100000000 == 0) { // 100 Million
		printf(".");

		if((*counter) % 1000000000 == 0) { // 1 Billion
			++(*billion);
			*counter = 0;
			printf("\nTried %d billion combinations, still not found..\n", *billion);
		}
	}

	return 0;
}

// Main
int main() {
	const char* table = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
	const int minLength = 1, maxLength = 12, maxChar = strlen(table);
	char* password = (char*)calloc(maxLength + 1, sizeof(char)),
		  *iteration = (char*)calloc(maxLength + 1, sizeof(char));
	unsigned int counter = 1, billion = 0;
	int i;

	for(i = minLength; i <= maxLength; ++i) {
		do { // Iterate every single combination with i length
			convertPassword(password, table, iteration, i);

			if(tryThePassword(iteration, PASSWORD_TO_CRACK, &counter, &billion)) return 0;
		} while(incrementPass(password, maxChar, i));

		// Clear password to start searching i + 1 length passwords
		memset(password, 0, i);
	}

	return 0;
}