149 lines
4.6 KiB
C
149 lines
4.6 KiB
C
/* hmac.c - TinyCrypt implementation of the HMAC algorithm */
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/*
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* Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* - Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* - Neither the name of Intel Corporation nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <tinycrypt/hmac.h>
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#include <tinycrypt/constants.h>
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#include <tinycrypt/utils.h>
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static void rekey(uint8_t *key, const uint8_t *new_key, unsigned int key_size)
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{
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const uint8_t inner_pad = (uint8_t) 0x36;
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const uint8_t outer_pad = (uint8_t) 0x5c;
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unsigned int i;
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for (i = 0; i < key_size; ++i) {
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key[i] = inner_pad ^ new_key[i];
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key[i + TC_SHA256_BLOCK_SIZE] = outer_pad ^ new_key[i];
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}
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for (; i < TC_SHA256_BLOCK_SIZE; ++i) {
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key[i] = inner_pad; key[i + TC_SHA256_BLOCK_SIZE] = outer_pad;
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}
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}
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int tc_hmac_set_key(TCHmacState_t ctx, const uint8_t *key,
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unsigned int key_size)
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{
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/* input sanity check: */
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if (ctx == (TCHmacState_t) 0 ||
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key == (const uint8_t *) 0 ||
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key_size == 0) {
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return TC_CRYPTO_FAIL;
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}
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const uint8_t dummy_key[key_size];
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struct tc_hmac_state_struct dummy_state;
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if (key_size <= TC_SHA256_BLOCK_SIZE) {
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/*
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* The next three lines consist of dummy calls just to avoid
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* certain timing attacks. Without these dummy calls,
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* adversaries would be able to learn whether the key_size is
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* greater than TC_SHA256_BLOCK_SIZE by measuring the time
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* consumed in this process.
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*/
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(void)tc_sha256_init(&dummy_state.hash_state);
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(void)tc_sha256_update(&dummy_state.hash_state,
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dummy_key,
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key_size);
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(void)tc_sha256_final(&dummy_state.key[TC_SHA256_DIGEST_SIZE],
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&dummy_state.hash_state);
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/* Actual code for when key_size <= TC_SHA256_BLOCK_SIZE: */
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rekey(ctx->key, key, key_size);
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} else {
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(void)tc_sha256_init(&ctx->hash_state);
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(void)tc_sha256_update(&ctx->hash_state, key, key_size);
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(void)tc_sha256_final(&ctx->key[TC_SHA256_DIGEST_SIZE],
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&ctx->hash_state);
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rekey(ctx->key,
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&ctx->key[TC_SHA256_DIGEST_SIZE],
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TC_SHA256_DIGEST_SIZE);
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}
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return TC_CRYPTO_SUCCESS;
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}
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int tc_hmac_init(TCHmacState_t ctx)
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{
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/* input sanity check: */
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if (ctx == (TCHmacState_t) 0) {
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return TC_CRYPTO_FAIL;
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}
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(void) tc_sha256_init(&ctx->hash_state);
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(void) tc_sha256_update(&ctx->hash_state, ctx->key, TC_SHA256_BLOCK_SIZE);
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return TC_CRYPTO_SUCCESS;
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}
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int tc_hmac_update(TCHmacState_t ctx,
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const void *data,
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unsigned int data_length)
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{
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/* input sanity check: */
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if (ctx == (TCHmacState_t) 0) {
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return TC_CRYPTO_FAIL;
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}
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(void)tc_sha256_update(&ctx->hash_state, data, data_length);
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return TC_CRYPTO_SUCCESS;
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}
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int tc_hmac_final(uint8_t *tag, unsigned int taglen, TCHmacState_t ctx)
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{
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/* input sanity check: */
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if (tag == (uint8_t *) 0 ||
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taglen != TC_SHA256_DIGEST_SIZE ||
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ctx == (TCHmacState_t) 0) {
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return TC_CRYPTO_FAIL;
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}
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(void) tc_sha256_final(tag, &ctx->hash_state);
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(void)tc_sha256_init(&ctx->hash_state);
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(void)tc_sha256_update(&ctx->hash_state,
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&ctx->key[TC_SHA256_BLOCK_SIZE],
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TC_SHA256_BLOCK_SIZE);
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(void)tc_sha256_update(&ctx->hash_state, tag, TC_SHA256_DIGEST_SIZE);
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(void)tc_sha256_final(tag, &ctx->hash_state);
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/* destroy the current state */
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_set(ctx, 0, sizeof(*ctx));
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return TC_CRYPTO_SUCCESS;
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}
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