diff options
| -rw-r--r-- | src/26_ctr_bitflipping.c | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/src/26_ctr_bitflipping.c b/src/26_ctr_bitflipping.c new file mode 100644 index 0000000..fa6c5c9 --- /dev/null +++ b/src/26_ctr_bitflipping.c @@ -0,0 +1,58 @@ +// CTR bitflipping +#include "aes.h" +#include "misc.h" +#include "random.h" +#include <assert.h> + +/* + * there aree people in the world that believe ctr resists bit flipping attacks + * of the kind to which cbc mode is susceptible. re-implement the cbc + * bitflipping exercise from earlier to use ctr mode instead of cbc mode. inject + * an "admin=true" token. + */ + +unsigned char *key; + +char *strip_special_chars(char *input, size_t input_len) { + char *res = (char *)malloc(input_len * sizeof(char)); + for (size_t i = 0; i < input_len; i++) + if (input[i] == ';' || input[i] == '=') + res[i] = ' '; + else + res[i] = input[i]; + return res; +} + +struct bytes strip_encrypt_ctr(char *data, size_t data_len) { + const char *prefix = "comment1=cooking%20MCs;userdata="; + const char *suffix = ";comment2=%20like%20a%20pound%20of%20bacon"; + size_t prefix_len = strlen(prefix); + size_t suffix_len = strlen(suffix); + size_t input_len = data_len + prefix_len + suffix_len; + char *input = (char *)malloc(input_len * sizeof(char)); + memcpy(input, prefix, prefix_len); + memcpy(input + prefix_len, data, data_len); + memcpy(input + prefix_len + data_len, suffix, suffix_len); + char *stripped = strip_special_chars(input, input_len); + struct bytes res = aes_ctr((unsigned char *)stripped, input_len, key, 16, 0); + free(input); + free(stripped); + return res; +} + +int main(void) { + srand(time(NULL)); + key = random_bytes(16); + const char *data = ":admin<true:"; + struct bytes encrypted = strip_encrypt_ctr((char *)data, strlen(data)); + encrypted.data[32] ^= 0x01; + encrypted.data[32 + 6] ^= 0x01; + encrypted.data[32 + 11] ^= 0x01; + struct bytes decrypted = aes_ctr(encrypted.data, encrypted.len, key, 16, 0); + const char *target = ";admin=true;"; + assert(contains(decrypted.data, decrypted.len, target)); + printf("Success: %s in decrypted data\n", target); + free(encrypted.data); + free(decrypted.data); + return 0; +} |
