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/* hmac.c - TinyCrypt implementation of the HMAC algorithm */
/*
* Copyright (C) 2015 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/hmac.h>
#include <tinycrypt/constants.h>
#include <tinycrypt/utils.h>
static void rekey(uint8_t *key, const uint8_t *new_key, uint32_t key_size)
{
const uint8_t inner_pad = (uint8_t) 0x36;
const uint8_t outer_pad = (uint8_t) 0x5c;
uint32_t i;
for (i = 0; i < key_size; ++i) {
key[i] = inner_pad ^ new_key[i];
key[i + TC_SHA256_BLOCK_SIZE] = outer_pad ^ new_key[i];
}
for (; i < TC_SHA256_BLOCK_SIZE; ++i) {
key[i] = inner_pad; key[i + TC_SHA256_BLOCK_SIZE] = outer_pad;
}
}
int32_t tc_hmac_set_key(TCHmacState_t ctx,
const uint8_t *key,
uint32_t key_size)
{
/* input sanity check: */
if (ctx == (TCHmacState_t) 0 ||
key == (const uint8_t *) 0 ||
key_size == 0) {
return TC_CRYPTO_FAIL;
}
const uint8_t dummy_key[key_size];
struct tc_hmac_state_struct dummy_state;
if (key_size <= TC_SHA256_BLOCK_SIZE) {
/*
* The next three lines consist of dummy calls just to avoid
* certain timing attacks. Without these dummy calls,
* adversaries would be able to learn whether the key_size is
* greater than TC_SHA256_BLOCK_SIZE by measuring the time
* consumed in this process.
*/
(void)tc_sha256_init(&dummy_state.hash_state);
(void)tc_sha256_update(&dummy_state.hash_state,
dummy_key,
key_size);
(void)tc_sha256_final(&dummy_state.key[TC_SHA256_DIGEST_SIZE],
&dummy_state.hash_state);
/* Actual code for when key_size <= TC_SHA256_BLOCK_SIZE: */
rekey(ctx->key, key, key_size);
} else {
(void)tc_sha256_init(&ctx->hash_state);
(void)tc_sha256_update(&ctx->hash_state, key, key_size);
(void)tc_sha256_final(&ctx->key[TC_SHA256_DIGEST_SIZE],
&ctx->hash_state);
rekey(ctx->key,
&ctx->key[TC_SHA256_DIGEST_SIZE],
TC_SHA256_DIGEST_SIZE);
}
return TC_CRYPTO_SUCCESS;
}
int32_t tc_hmac_init(TCHmacState_t ctx)
{
/* input sanity check: */
if (ctx == (TCHmacState_t) 0 ||
ctx->key == (uint8_t *) 0) {
return TC_CRYPTO_FAIL;
}
(void)tc_sha256_init(&ctx->hash_state);
(void)tc_sha256_update(&ctx->hash_state,
ctx->key,
TC_SHA256_BLOCK_SIZE);
return TC_CRYPTO_SUCCESS;
}
int32_t tc_hmac_update(TCHmacState_t ctx,
const void *data,
uint32_t data_length)
{
/* input sanity check: */
if (ctx == (TCHmacState_t) 0 || ctx->key == (uint8_t *) 0) {
return TC_CRYPTO_FAIL;
}
(void)tc_sha256_update(&ctx->hash_state, data, data_length);
return TC_CRYPTO_SUCCESS;
}
int32_t tc_hmac_final(uint8_t *tag, uint32_t taglen, TCHmacState_t ctx)
{
/* input sanity check: */
if (tag == (uint8_t *) 0 ||
taglen != TC_SHA256_DIGEST_SIZE ||
ctx == (TCHmacState_t) 0 ||
ctx->key == (uint8_t *) 0) {
return TC_CRYPTO_FAIL;
}
(void) tc_sha256_final(tag, &ctx->hash_state);
(void)tc_sha256_init(&ctx->hash_state);
(void)tc_sha256_update(&ctx->hash_state,
&ctx->key[TC_SHA256_BLOCK_SIZE],
TC_SHA256_BLOCK_SIZE);
(void)tc_sha256_update(&ctx->hash_state, tag, TC_SHA256_DIGEST_SIZE);
(void)tc_sha256_final(tag, &ctx->hash_state);
/* destroy the current state */
_set(ctx, 0, sizeof(*ctx));
return TC_CRYPTO_SUCCESS;
}
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