/* 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 <hmac.h>
#include <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_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_SUCCESS;
}

int32_t tc_hmac_init(TCHmacState_t ctx)
{
        /* input sanity check: */
        if (ctx == (TCHmacState_t) 0 ||
            ctx->key == (uint8_t *) 0) {
                return TC_FAIL;
        }

        (void)tc_sha256_init(&ctx->hash_state);
        (void)tc_sha256_update(&ctx->hash_state, ctx->key, TC_SHA256_BLOCK_SIZE);

        return TC_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_FAIL;
        }

        (void)tc_sha256_update(&ctx->hash_state, data, data_length);

        return TC_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_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);

        return TC_SUCCESS;
}