/* hmac.c - TinyCrypt implementation of the HMAC algorithm */

/*
    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/hmac.h>
#include <tinycrypt/constants.h>
#include <tinycrypt/utils.h>

static void rekey(uint8_t* key, const uint8_t* new_key, unsigned int key_size)
{
    const uint8_t inner_pad = (uint8_t) 0x36;
    const uint8_t outer_pad = (uint8_t) 0x5c;
    unsigned int 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;
    }
}

int tc_hmac_set_key(TCHmacState_t ctx, const uint8_t* key,
                    unsigned int 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;
}

int tc_hmac_init(TCHmacState_t ctx)
{
    /* input sanity check: */
    if (ctx == (TCHmacState_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;
}

int tc_hmac_update(TCHmacState_t ctx,
                   const void* data,
                   unsigned int data_length)
{
    /* input sanity check: */
    if (ctx == (TCHmacState_t) 0)
    {
        return TC_CRYPTO_FAIL;
    }

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

int tc_hmac_final(uint8_t* tag, unsigned int taglen, TCHmacState_t ctx)
{
    /* input sanity check: */
    if (tag == (uint8_t*) 0 ||
            taglen != TC_SHA256_DIGEST_SIZE ||
            ctx == (TCHmacState_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;
}
