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/* cmac_mode.c - TinyCrypt CMAC mode implementation */
/*
* Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* - Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Intel Corporation nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <tinycrypt/aes.h>
#include <tinycrypt/cmac_mode.h>
#include <tinycrypt/constants.h>
#include <tinycrypt/utils.h>
/* max number of calls until change the key (2^48).*/
const static uint64_t MAX_CALLS = ((uint64_t)1 << 48);
/*
* gf_wrap -- In our implementation, GF(2^128) is represented as a 16 byte
* array with byte 0 the most significant and byte 15 the least significant.
* High bit carry reduction is based on the primitive polynomial
*
* X^128 + X^7 + X^2 + X + 1,
*
* which leads to the reduction formula X^128 = X^7 + X^2 + X + 1. Indeed,
* since 0 = (X^128 + X^7 + X^2 + 1) mod (X^128 + X^7 + X^2 + X + 1) and since
* addition of polynomials with coefficients in Z/Z(2) is just XOR, we can
* add X^128 to both sides to get
*
* X^128 = (X^7 + X^2 + X + 1) mod (X^128 + X^7 + X^2 + X + 1)
*
* and the coefficients of the polynomial on the right hand side form the
* string 1000 0111 = 0x87, which is the value of gf_wrap.
*
* This gets used in the following way. Doubling in GF(2^128) is just a left
* shift by 1 bit, except when the most significant bit is 1. In the latter
* case, the relation X^128 = X^7 + X^2 + X + 1 says that the high order bit
* that overflows beyond 128 bits can be replaced by addition of
* X^7 + X^2 + X + 1 <--> 0x87 to the low order 128 bits. Since addition
* in GF(2^128) is represented by XOR, we therefore only have to XOR 0x87
* into the low order byte after a left shift when the starting high order
* bit is 1.
*/
const unsigned char gf_wrap = 0x87;
/*
* assumes: out != NULL and points to a GF(2^n) value to receive the
* doubled value;
* in != NULL and points to a 16 byte GF(2^n) value
* to double;
* the in and out buffers do not overlap.
* effects: doubles the GF(2^n) value pointed to by "in" and places
* the result in the GF(2^n) value pointed to by "out."
*/
void gf_double(uint8_t *out, uint8_t *in)
{
/* start with low order byte */
uint8_t *x = in + (TC_AES_BLOCK_SIZE - 1);
/* if msb == 1, we need to add the gf_wrap value, otherwise add 0 */
uint8_t carry = (in[0] >> 7) ? gf_wrap : 0;
out += (TC_AES_BLOCK_SIZE - 1);
for (;;) {
*out-- = (*x << 1) ^ carry;
if (x == in) {
break;
}
carry = *x-- >> 7;
}
}
int tc_cmac_setup(TCCmacState_t s, const uint8_t *key, TCAesKeySched_t sched)
{
/* input sanity check: */
if (s == (TCCmacState_t) 0 ||
key == (const uint8_t *) 0) {
return TC_CRYPTO_FAIL;
}
/* put s into a known state */
_set(s, 0, sizeof(*s));
s->sched = sched;
/* configure the encryption key used by the underlying block cipher */
tc_aes128_set_encrypt_key(s->sched, key);
/* compute s->K1 and s->K2 from s->iv using s->keyid */
_set(s->iv, 0, TC_AES_BLOCK_SIZE);
tc_aes_encrypt(s->iv, s->iv, s->sched);
gf_double (s->K1, s->iv);
gf_double (s->K2, s->K1);
/* reset s->iv to 0 in case someone wants to compute now */
tc_cmac_init(s);
return TC_CRYPTO_SUCCESS;
}
int tc_cmac_erase(TCCmacState_t s)
{
if (s == (TCCmacState_t) 0) {
return TC_CRYPTO_FAIL;
}
/* destroy the current state */
_set(s, 0, sizeof(*s));
return TC_CRYPTO_SUCCESS;
}
int tc_cmac_init(TCCmacState_t s)
{
/* input sanity check: */
if (s == (TCCmacState_t) 0) {
return TC_CRYPTO_FAIL;
}
/* CMAC starts with an all zero initialization vector */
_set(s->iv, 0, TC_AES_BLOCK_SIZE);
/* and the leftover buffer is empty */
_set(s->leftover, 0, TC_AES_BLOCK_SIZE);
s->leftover_offset = 0;
/* Set countdown to max number of calls allowed before re-keying: */
s->countdown = MAX_CALLS;
return TC_CRYPTO_SUCCESS;
}
int tc_cmac_update(TCCmacState_t s, const uint8_t *data, size_t data_length)
{
unsigned int i;
/* input sanity check: */
if (s == (TCCmacState_t) 0) {
return TC_CRYPTO_FAIL;
}
if (data_length == 0) {
return TC_CRYPTO_SUCCESS;
}
if (data == (const uint8_t *) 0) {
return TC_CRYPTO_FAIL;
}
if (s->countdown == 0) {
return TC_CRYPTO_FAIL;
}
s->countdown--;
if (s->leftover_offset > 0) {
/* last data added to s didn't end on a TC_AES_BLOCK_SIZE byte boundary */
size_t remaining_space = TC_AES_BLOCK_SIZE - s->leftover_offset;
if (data_length < remaining_space) {
/* still not enough data to encrypt this time either */
_copy(&s->leftover[s->leftover_offset], data_length, data, data_length);
s->leftover_offset += data_length;
return TC_CRYPTO_SUCCESS;
}
/* leftover block is now full; encrypt it first */
_copy(&s->leftover[s->leftover_offset],
remaining_space,
data,
remaining_space);
data_length -= remaining_space;
data += remaining_space;
s->leftover_offset = 0;
for (i = 0; i < TC_AES_BLOCK_SIZE; ++i) {
s->iv[i] ^= s->leftover[i];
}
tc_aes_encrypt(s->iv, s->iv, s->sched);
}
/* CBC encrypt each (except the last) of the data blocks */
while (data_length > TC_AES_BLOCK_SIZE) {
for (i = 0; i < TC_AES_BLOCK_SIZE; ++i) {
s->iv[i] ^= data[i];
}
tc_aes_encrypt(s->iv, s->iv, s->sched);
data += TC_AES_BLOCK_SIZE;
data_length -= TC_AES_BLOCK_SIZE;
}
if (data_length > 0) {
/* save leftover data for next time */
_copy(s->leftover, data_length, data, data_length);
s->leftover_offset = data_length;
}
return TC_CRYPTO_SUCCESS;
}
int tc_cmac_final(uint8_t *tag, TCCmacState_t s)
{
uint8_t *k;
unsigned int i;
/* input sanity check: */
if (tag == (uint8_t *) 0 ||
s == (TCCmacState_t) 0) {
return TC_CRYPTO_FAIL;
}
if (s->leftover_offset == TC_AES_BLOCK_SIZE) {
/* the last message block is a full-sized block */
k = (uint8_t *) s->K1;
} else {
/* the final message block is not a full-sized block */
size_t remaining = TC_AES_BLOCK_SIZE - s->leftover_offset;
_set(&s->leftover[s->leftover_offset], 0, remaining);
s->leftover[s->leftover_offset] = TC_CMAC_PADDING;
k = (uint8_t *) s->K2;
}
for (i = 0; i < TC_AES_BLOCK_SIZE; ++i) {
s->iv[i] ^= s->leftover[i] ^ k[i];
}
tc_aes_encrypt(tag, s->iv, s->sched);
/* erasing state: */
tc_cmac_erase(s);
return TC_CRYPTO_SUCCESS;
}
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