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Reverse Engineering a Book Cover: bruteforcing crc32 values
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| //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; | |
| } |
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