diff options
| -rw-r--r-- | main.c | 44 |
1 files changed, 29 insertions, 15 deletions
@@ -9,7 +9,9 @@ #include <tomcrypt.h> -const char *hexchars = "0123456789ABCDEF"; +/* because DES discards all LSBs of every byte, + * the hex alphabet can be reduced by masking out LSB from all characters */ +const char *hexchars = "02468@BDF"; int pkcs7_check_pad(const char *buf, size_t n); @@ -52,8 +54,8 @@ bool yield_possible_key( // const char[] hexchars = {0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, // 0x38, 0x39, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46}; #define FILL_KEY(buf, key, i) \ - ((buf)[7-(i)] = hexchars[((key) >> (4*(i))) & 0xFu]) \ - // buf: char[8], key: uint64_t, i:uint = 0, 1, 2, ..., 7 + do { ((buf)[7-(i)] = hexchars[(key)%9u]); (key) /= 9u; } while(0) + // buf: char[8], key: uint64_t (high bits unused), i:uint = 0, 1, 2, ..., 7 uint32_t k = ctx->next_possible_key; uint64_t plaintext; char key[8]; @@ -64,15 +66,18 @@ bool yield_possible_key( ctx->finished = true; return false; } - // convert key uint32 to char[] - FILL_KEY(key, k, 0); - FILL_KEY(key, k, 1); - FILL_KEY(key, k, 2); - FILL_KEY(key, k, 3); - FILL_KEY(key, k, 4); - FILL_KEY(key, k, 5); - FILL_KEY(key, k, 6); - FILL_KEY(key, k, 7); + /* convert key uint32 to char[], + * here FILL_KEY will modify key, + * so we use a temp variable */ + uint32_t k_tmp = k; + FILL_KEY(key, k_tmp, 0); + FILL_KEY(key, k_tmp, 1); + FILL_KEY(key, k_tmp, 2); + FILL_KEY(key, k_tmp, 3); + FILL_KEY(key, k_tmp, 4); + FILL_KEY(key, k_tmp, 5); + FILL_KEY(key, k_tmp, 6); + FILL_KEY(key, k_tmp, 7); // decrypt file header with this key int err; if ((err = des_setup((const unsigned char *) key, 8, 0, &skey)) != @@ -211,7 +216,10 @@ int thread_worker(thread_param *param) { snprintf(md5_hex, 8 + 1, "%02X%02X%02X%02X", md5_out[0] & 0xFFu, md5_out[1] & 0xFFu, md5_out[2] & 0xFFu, md5_out[3] & 0xFFu); - if (!memcmp(md5_hex, (const char *) (&ctx.yield), 8)) { + /* since we have discarded the LSBs of every byte of the key, + * we always yield keys whose bytes all have their LSB equals to 0. + * So we mask out the LSBs from md5_hex before comparing */ + if (ctx.yield == ((*(uint64_t *) md5_hex) & 0xFEFEFEFEFEFEFEFEull)) { atomic_store(&key_found, true); printf("[+] FOUND KEY: %s\n", md5_hex); crack_result.plaintext = plaintext; @@ -340,14 +348,18 @@ int main(int argc, char *argv[]) { } /* assign search ranges to workers */ - uint32_t range_size = 0xFFFFFFFFu / threads; + /* powl(9,8) == 43046721, + * the key is about 25.3594 bits, + * a very small space for brute-force searching */ +#define KEYSPACE_SIZE 43046721u + uint32_t range_size = KEYSPACE_SIZE / threads; for (int i = 0; i < threads; ++i) { thread_params[i].a = range_size * i; thread_params[i].b = range_size * i + range_size; thread_params[i].worker_id = i; } /* the last search range should warp */ - thread_params[threads - 1].b = 0; + thread_params[threads - 1].b = KEYSPACE_SIZE; /* start workers */ for (int i = 0; i < threads; ++i) { @@ -380,6 +392,8 @@ int main(int argc, char *argv[]) { fclose(fout); printf("Flash photo has been saved in: %s\n", plaintext_save_path); + } else { + printf("[-] KEY WAS NOT FOUND.\n"); } return 0; |