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#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include "ae-common.h"
#include "cipher.h"
#include "lilliput-ae.h"
static void _init_msg_tweak(const uint8_t tag[TAG_BYTES], uint8_t tweak[TWEAK_BYTES])
{
/* The t-bit tweak is filled as follows:
*
* - bits [ 1, t-1]: tag + block index
* [ 1, 64]: tag[ 1.. 64] XOR block index
* [ 65, t-1]: tag[65..t-1]
* - bit t: 1
*/
memcpy(tweak+sizeof(uint64_t), tag+sizeof(uint64_t), TAG_BYTES-sizeof(uint64_t));
tweak[TWEAK_BYTES-1] |= 0x80;
}
static void _fill_msg_tweak(const uint8_t tag[TAG_BYTES], uint64_t block_index, uint8_t tweak[TWEAK_BYTES])
{
/* Assume bits 65 to t-1 are set. */
for (size_t i=0; i<sizeof(block_index); i++)
{
uint8_t index_i = block_index >> i*8 & 0xff;
tweak[i] = tag[i] ^ index_i;
}
}
static void _fill_tag_tweak(const uint8_t N[NONCE_BYTES], uint8_t tweak[TWEAK_BYTES])
{
/* The t-bit tweak is filled as follows:
*
* - bits [ 1, t-7]: N
* - bits [t-7, t]: 0001||0^4
*/
memcpy(tweak, N, TWEAK_BYTES-1);
tweak[TWEAK_BYTES-1] = 0x10;
}
static void _generate_tag(
const uint8_t key[KEY_BYTES],
size_t M_len,
const uint8_t M[M_len],
const uint8_t N[NONCE_BYTES],
const uint8_t Auth[BLOCK_BYTES],
uint8_t tag[TAG_BYTES]
)
{
uint8_t Ek_Mj[BLOCK_BYTES];
uint8_t tag_tmp[TAG_BYTES];
uint8_t tweak[TWEAK_BYTES];
memset(tweak, 0, TWEAK_BYTES);
memcpy(tag_tmp, Auth, TAG_BYTES);
size_t l = M_len / BLOCK_BYTES;
size_t rest = M_len % BLOCK_BYTES;
for (size_t j=0; j<l; j++)
{
fill_index_tweak(0x0, j, tweak);
encrypt(key, tweak, &M[j*BLOCK_BYTES], Ek_Mj);
xor_into(tag_tmp, Ek_Mj);
}
if (rest != 0)
{
uint8_t M_rest[BLOCK_BYTES];
pad10(rest, &M[l*BLOCK_BYTES], M_rest);
fill_index_tweak(0x4, l, tweak);
encrypt(key, tweak, M_rest, Ek_Mj);
xor_into(tag_tmp, Ek_Mj);
}
_fill_tag_tweak(N, tweak);
encrypt(key, tweak, tag_tmp, tag);
}
static void _encrypt_message(
const uint8_t key[KEY_BYTES],
size_t M_len,
const uint8_t M[M_len],
const uint8_t N[NONCE_BYTES],
const uint8_t tag[TAG_BYTES],
uint8_t C[M_len]
)
{
uint8_t Ek_N[BLOCK_BYTES];
uint8_t tweak[TWEAK_BYTES];
_init_msg_tweak(tag, tweak);
uint8_t padded_N[BLOCK_BYTES];
memcpy(padded_N, N, NONCE_BYTES);
padded_N[BLOCK_BYTES-1] = 0;
size_t l = M_len / BLOCK_BYTES;
size_t rest = M_len % BLOCK_BYTES;
for (size_t j=0; j<l; j++)
{
_fill_msg_tweak(tag, j, tweak);
encrypt(key, tweak, padded_N, Ek_N);
xor_arrays(BLOCK_BYTES, &C[j*BLOCK_BYTES], &M[j*BLOCK_BYTES], Ek_N);
}
if (rest != 0)
{
_fill_msg_tweak(tag, l, tweak);
encrypt(key, tweak, padded_N, Ek_N);
xor_arrays(rest, &C[l*BLOCK_BYTES], &M[l*BLOCK_BYTES], Ek_N);
}
}
void lilliput_ae_encrypt(
size_t message_len,
const uint8_t message[message_len],
size_t auth_data_len,
const uint8_t auth_data[auth_data_len],
const uint8_t key[KEY_BYTES],
const uint8_t nonce[NONCE_BYTES],
uint8_t ciphertext[message_len],
uint8_t tag[TAG_BYTES]
)
{
uint8_t auth[BLOCK_BYTES];
process_associated_data(key, auth_data_len, auth_data, auth);
_generate_tag(key, message_len, message, nonce, auth, tag);
_encrypt_message(key, message_len, message, nonce, tag, ciphertext);
}
bool lilliput_ae_decrypt(
size_t ciphertext_len,
const uint8_t ciphertext[ciphertext_len],
size_t auth_data_len,
const uint8_t auth_data[auth_data_len],
const uint8_t key[KEY_BYTES],
const uint8_t nonce[NONCE_BYTES],
const uint8_t tag[TAG_BYTES],
uint8_t message[ciphertext_len]
)
{
_encrypt_message(key, ciphertext_len, ciphertext, nonce, tag, message);
uint8_t auth[BLOCK_BYTES];
process_associated_data(key, auth_data_len, auth_data, auth);
uint8_t effective_tag[TAG_BYTES];
_generate_tag(key, ciphertext_len, message, nonce, auth, effective_tag);
return memcmp(tag, effective_tag, TAG_BYTES) == 0;
}
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