path: root/lib/lib3.c

#include "lib3.h"
#include "lib2.h"
#include "lib.h"


#define NR_STIRNGS_CHALLENGE17 10

char *challenge17_encrypt(int *length)
{
	int i, t;
	char **string;
	char **decoded;
	string = malloc(sizeof(char *)*NR_STIRNGS_CHALLENGE17);
	decoded = malloc(sizeof(char *)*NR_STIRNGS_CHALLENGE17);
	char filename[] = "task17_0";	

	for(i=0;i<10;i++) {
		filename[strlen(filename)-1] = (char) (i+'0');
		t = read_base64_file(filename, &string[i]);
		decoded[i] = malloc(t);
		length[i] = decode_base64(string[i], decoded[i]);
		printf("read: %s\n", string[i]);
	}
	// choose one randomly
	int random = rand() % NR_STIRNGS_CHALLENGE17;
	int padding;
	printf("plaintext: %s\n", string[random]);
	*length = strlen(string[random]);
	char *padded_string = __pkcs7_padding(string[random], *length, 16, &padding);
	char *encrypted = malloc(strlen(padded_string));
	*length += padding;
	aes_cbc(padded_string, strlen(padded_string), encrypted, key, iv, 1);
	return encrypted;	
}

int cbc_padding_oracle(char *encrypted, int length)
{
	char *decrypted = malloc(length);
	char *unpadded= malloc(length);
	
	aes_cbc(encrypted, length, decrypted, key, iv, 0);

	int valid = valid_pkcs7_padding(decrypted, length, unpadded, 16);
	free(decrypted);
	free(unpadded);
	return valid;

}

/**
  * format is: 64 nonce concat with 64 bit counter
  * calle has to make sure that nonce is at least 8 bytes
  * its all little endian
  */
int aes_ctr(char *in, int length_in, char *out, char *string_key, char *nonce)
{
	long counter;
	unsigned char tmp[16];
	char keystream[16];
	long nr_blocks = length_in / BLOCKSIZE;
	int length_last_block = length_in % BLOCKSIZE;
	memcpy(tmp, nonce, 16);

	for(counter=0;counter<nr_blocks-1;counter++) {
		// right now it only works for 256 block :P 
		tmp[8] = counter % 256;
		// encrypt nonce and counter and produce keystream
		aes_ecb(tmp, 16, keystream, string_key, 16, 1);
		// xor against keystream to encrpy/decrypt
		xor_string(&in[counter*BLOCKSIZE], keystream, &out[counter*BLOCKSIZE], 16, 16); 
	}

	// do last block
	tmp[8] = counter % 256;
	aes_ecb(tmp, 16, keystream, string_key, 16, 1);
	xor_string(&in[counter*BLOCKSIZE], keystream, &out[counter*BLOCKSIZE],
			16, length_last_block);

}

void mt_19937_seed(unsigned int seed, struct mt_19937_state *mt_19937)
{
	int i;

	mt_19937->index = MT_19937_N;
	mt_19937->mt[0] = seed;
	memset(&mt_19937->mt[1], 0, 623);
	for(i=1;i<=MT_19937_N;i++) {
		mt_19937->mt[i] = (1812433253 * (mt_19937->mt[i-1]
			^ (mt_19937->mt[i-1] >> 30))) + i;
		// only the last 32 bit
		mt_19937->mt[i] &= 0xFFFFFFFF;
	}
}

void mt_19937_generate(struct mt_19937_state *mt_19937)
{
	unsigned int i, x;

	for(i=0;i<=MT_19937_N;i++) {
		// x is the first bit of mt[i] plus the last 31 bits of the
		// next number
		x = (((mt_19937->mt[i] & MT_19937_UPPER_MASK) + 
			(mt_19937->mt[(i+1) % 624] & MT_19937_LOWER_MASK)
		   	)& 0xFFFFFFFF);
		
		mt_19937->mt[i] = mt_19937->mt[(i+397) % MT_19937_N] ^ x >> 1;	

		if (x % 2)
			mt_19937->mt[i] ^= 0x9908b0df;
	}
	mt_19937->index = 0;
}


unsigned int mt_19937(struct mt_19937_state *mt_19937_st)
{
	unsigned int y = 0x0;

	if(mt_19937_st->index >= MT_19937_N)
		mt_19937_generate(mt_19937_st);

	y = mt_19937_st->mt[mt_19937_st->index];

	y = y ^ (y >> 11);
	y = y ^ ((y << 7) & 0x9D2C5680);
	y = y ^ ((y << 15) & 0xEFC60000);
	y = y ^ (y >> 18);

	mt_19937_st->index++;

	return (y & 0xFFFFFFFF);
}

unsigned int mt_19937_timestamp_orcale(struct mt_19937_state *mt_19937_st)
{
	sleep(random_number_between(40,1000));

	unsigned int seed = time(NULL);
	printf("timestamp orcale seed: %u\n", seed);
	mt_19937_seed(seed, mt_19937_st);

	sleep(random_number_between(40,1000));

	return  mt_19937(mt_19937_st);
}
/***
  * is there a more clever way to do this than brute force?
  *
  **/
void mt_19937_brute_force_timestamp()
{
	struct mt_19937_state mt_state;
	unsigned int start = time(NULL);
	int rnd = mt_19937_timestamp_orcale(&mt_state);
	unsigned int stop = time(NULL);
	unsigned int i;
	// try every seed between start and stop
	for(i=start;start<=stop;i++) {
		mt_19937_seed(i, &mt_state);
		if (rnd == mt_19937(&mt_state)) {
			printf("found seed: %u\n", i);
			break;
		}
	}
}

int unshift_right_xor(int number, int shifts)
{
	/**
	  * restore shift bits in every round
	 **/
	int rounds = 0;
	int restore = 0;

	while(rounds*shifts < 32) {
		// take #shift bit be on, begin on the left and go to the right
		unsigned int tmp = (0xFFFFFFFF << (32-shifts)) >> (rounds*shifts);
		unsigned int tmp2 = number & tmp;
		number ^= tmp2 >> shifts;
		restore |= tmp2;
		rounds++;
	}
	return restore;
}

/***
  * why the fuck is the reverse AND working?
  **/
int unshift_left_xor(int number, int shifts, unsigned int mask)
{
	int rounds = 0;
	int restore = 0;

	while(rounds*shifts < 32) {
		// take #shift bit be on, begin on the right and shift it to left every round
		unsigned int tmp = (0xFFFFFFFF >> (32-shifts)) << (rounds*shifts);
		unsigned int tmp2 = number & tmp;
		number ^= tmp2 << shifts & mask;
		restore |= tmp2;
		rounds++;
	}
	return restore;
}


int mt_19937_stream_cipher(char *in, int length_in, char *out, int seed)
{
	struct mt_19937_state mt_state;
	char keystream;
	int i, tmp;

	mt_19937_seed(seed, &mt_state);

	for(i=0;i<length_in;i++) {
		tmp = mt_19937(&mt_state);
		keystream = tmp & 0xFF;
		out[i] = in[i] ^ keystream;
	}
}

int mt_19937_stream_cipher_oracle(char *in, int length_in, char *out)
{
	int prefix_length = random_number_between(0,50);
	// only 16 bit seed, 0 would not be a good seed, since the keystream
	// would allways be 0
	int seed = random_number_between(1,65536);
	char *plaintext_full = malloc(length_in + prefix_length);

	printf("use seed: %i\n", seed);
	// generate random number of random bytes
	generate_random_bytes(plaintext_full, prefix_length);
	memcpy(&plaintext_full[prefix_length], in, length_in);

	mt_19937_stream_cipher(plaintext_full, (length_in+prefix_length),
			out, seed);

	return (length_in + prefix_length);
}


int crack_mt_19937_stream_cipher_16_bit_seed(char *ciphertext, int length_ciphertext,
		char *plaintext, char *match)
{
	int i;
	int seed;
	int match_len = strlen(match);
	for(seed=1;seed<65536;seed++) {
		mt_19937_stream_cipher(ciphertext, length_ciphertext, plaintext, seed);
		for(i=1;i<match_len;i++) {
			if(plaintext[length_ciphertext-i] != match[match_len-i]) {
				break;
			}
			else if (i == (match_len-1))
				goto out;
		}
	}
out:
	printf("found seed: %i\n", seed);
}

unsigned int mt_19937_password_token()
{
	int seed = time(NULL);
	struct mt_19937_state mt_state;
	printf("password token seed: %i\n", seed);	
	mt_19937_seed(seed, &mt_state);

	return mt_19937(&mt_state);
}

int mt_19937_password_token_time_based(unsigned int password_token, int time_window)
{
	int start_time = time(NULL);
	struct mt_19937_state mt_state;
	int seed;
	for(seed=start_time-(time_window*60);seed<start_time+(time_window*60);seed++) {
		mt_19937_seed(seed, &mt_state);
		if(password_token == mt_19937(&mt_state))
			return 1;
	}
	return 0;
}