Reverse Engineering a Book Cover: bruteforcing crc32 values

crc32_brute.c

//gcc -msse4.2 brute.c
#include <stdio.h>
int crc32(int crc, char c) {
	return __builtin_ia32_crc32qi(crc, c);
}

int main() {
	int value = 0;
	int tableIndex = 22;
	int table[] = {0x564d94ce,0x56487985,0xcd6966e6,0x791b5538,0xbdc0bfb7,0x8ecbf593,0xc652c4a2,0x94a3ebf7,0x2673b49e,0x89f7731e,0x32c1eb44,0x7886f083,0x52e2bb44,0xc7fdffaa,0x69f9005a,0xe04743ac,0x44229524,0xe8032961,0x8cc30f1e,0x084cdea3,0xeb48d1ad,0x90809740,0xe4292d5a };
	char password[24] = {};
	char *pwdpos = &password[22];

	while (tableIndex >= 0) {
		//printf("bruting pos %d...", pwdpos - password);
		for (unsigned char c = 0; c < 256; c++) {
			int crc = crc32(0, c);
			for (char *d = pwdpos+1; d - password <= 22; d++) {
				crc = crc32(crc, *d);
			}
			if (crc == table[tableIndex]) {
				//printf("%c\n", c);
				*pwdpos-- = c;
				--tableIndex;
				break;
			} else if (c == 255) {
				//printf("couldn't determine char for pos %d\n", pwdpos - password);
				return -1;
			}
		}
	}
	printf("password is '%s'\n", password);
	return 0;
}