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// https://cryptopals.com/sets/3/challenges/19
// https://cryptopals.com/sets/3/challenges/20
#include "util/aes.h"
#include "util/base64.h"
#include "util/random.h"
#include "util/score.h"
/* [challenge 20]
* data/c20_s3.txt contains base64'd plaintext. solve by using repeating-key
* XOR'd algorithm. CTR encryption appears different from repeated-key XOR, but
* with a fixed nonce, they are effectively the same thing. to make use of this
* "exploit", take collection of ciphertexts and trucate them to a common
* length. solve resulting concatenation of ciphertexts as if for repeating-key
* XOR, with a key size of the legnth of ciphertext.
*/
unsigned char key[16];
char *strings[] = {"SSBoYXZlIG1ldCB0aGVtIGF0IGNsb3NlIG9mIGRheQ==",
"Q29taW5nIHdpdGggdml2aWQgZmFjZXM=",
"RnJvbSBjb3VudGVyIG9yIGRlc2sgYW1vbmcgZ3JleQ==",
"RWlnaHRlZW50aC1jZW50dXJ5IGhvdXNlcy4=",
"SSBoYXZlIHBhc3NlZCB3aXRoIGEgbm9kIG9mIHRoZSBoZWFk",
"T3IgcG9saXRlIG1lYW5pbmdsZXNzIHdvcmRzLA==",
"T3IgaGF2ZSBsaW5nZXJlZCBhd2hpbGUgYW5kIHNhaWQ=",
"UG9saXRlIG1lYW5pbmdsZXNzIHdvcmRzLA==",
"QW5kIHRob3VnaHQgYmVmb3JlIEkgaGFkIGRvbmU=",
"T2YgYSBtb2NraW5nIHRhbGUgb3IgYSBnaWJl",
"VG8gcGxlYXNlIGEgY29tcGFuaW9u",
"QXJvdW5kIHRoZSBmaXJlIGF0IHRoZSBjbHViLA==",
"QmVpbmcgY2VydGFpbiB0aGF0IHRoZXkgYW5kIEk=",
"QnV0IGxpdmVkIHdoZXJlIG1vdGxleSBpcyB3b3JuOg==",
"QWxsIGNoYW5nZWQsIGNoYW5nZWQgdXR0ZXJseTo=",
"QSB0ZXJyaWJsZSBiZWF1dHkgaXMgYm9ybi4=",
"VGhhdCB3b21hbidzIGRheXMgd2VyZSBzcGVudA==",
"SW4gaWdub3JhbnQgZ29vZCB3aWxsLA==",
"SGVyIG5pZ2h0cyBpbiBhcmd1bWVudA==",
"VW50aWwgaGVyIHZvaWNlIGdyZXcgc2hyaWxsLg==",
"V2hhdCB2b2ljZSBtb3JlIHN3ZWV0IHRoYW4gaGVycw==",
"V2hlbiB5b3VuZyBhbmQgYmVhdXRpZnVsLA==",
"U2hlIHJvZGUgdG8gaGFycmllcnM/",
"VGhpcyBtYW4gaGFkIGtlcHQgYSBzY2hvb2w=",
"QW5kIHJvZGUgb3VyIHdpbmdlZCBob3JzZS4=",
"VGhpcyBvdGhlciBoaXMgaGVscGVyIGFuZCBmcmllbmQ=",
"V2FzIGNvbWluZyBpbnRvIGhpcyBmb3JjZTs=",
"SGUgbWlnaHQgaGF2ZSB3b24gZmFtZSBpbiB0aGUgZW5kLA==",
"U28gc2Vuc2l0aXZlIGhpcyBuYXR1cmUgc2VlbWVkLA==",
"U28gZGFyaW5nIGFuZCBzd2VldCBoaXMgdGhvdWdodC4=",
"VGhpcyBvdGhlciBtYW4gSSBoYWQgZHJlYW1lZA==",
"QSBkcnVua2VuLCB2YWluLWdsb3Jpb3VzIGxvdXQu",
"SGUgaGFkIGRvbmUgbW9zdCBiaXR0ZXIgd3Jvbmc=",
"VG8gc29tZSB3aG8gYXJlIG5lYXIgbXkgaGVhcnQs",
"WWV0IEkgbnVtYmVyIGhpbSBpbiB0aGUgc29uZzs=",
"SGUsIHRvbywgaGFzIHJlc2lnbmVkIGhpcyBwYXJ0",
"SW4gdGhlIGNhc3VhbCBjb21lZHk7",
"SGUsIHRvbywgaGFzIGJlZW4gY2hhbmdlZCBpbiBoaXMgdHVybiw=",
"VHJhbnNmb3JtZWQgdXR0ZXJseTo=",
"QSB0ZXJyaWJsZSBiZWF1dHkgaXMgYm9ybi4="};
int main() {
init_with_random_bytes(key, 16);
size_t arr_len = sizeof(strings) / sizeof(strings[0]);
unsigned char *outs[arr_len];
size_t lens[arr_len], max_len = 0;
// encrypt with random key
for (uint i = 0; i < arr_len; i++) {
size_t in_len;
uint8_t *in = base64_decode(strings[i], &in_len);
outs[i] = malloc(in_len);
lens[i] = in_len;
if (in_len > max_len)
max_len = in_len;
if (!ctr_encrypt(in, (int)in_len, key, 0, outs[i])) {
fprintf(stderr, "ctr_encrypt failed\n");
exit(1);
}
}
uint8_t buf[arr_len], key_stream[max_len];
for (uint j = 0; j < max_len; j++) {
size_t cnt = 0;
for (uint i = 0; i < arr_len; i++)
if (j < lens[i])
buf[cnt++] = outs[i][j];
key_stream[j] = best_key_step(buf, cnt, 0, 1);
}
// print decrypted result (last characters
// of lines are too difficult to break)
for (uint i = 0; i < arr_len; i++)
for (uint j = 0; j < max_len; j++) {
if (j < lens[i])
printf("%c\n", outs[i][j] ^ key_stream[j]);
else
break;
}
return 0;
}
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