/* cbc_mode.c - TinyCrypt implementation of CBC mode encryption & decryption */

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

int tc_cbc_mode_encrypt(uint8_t* out, unsigned int outlen, const uint8_t* in,
                        unsigned int inlen, const uint8_t* iv,
                        const TCAesKeySched_t sched)
{
    uint8_t buffer[TC_AES_BLOCK_SIZE];
    unsigned int n, m;

    /* input sanity check: */
    if (out == (uint8_t*) 0 ||
            in == (const uint8_t*) 0 ||
            sched == (TCAesKeySched_t) 0 ||
            inlen == 0 ||
            outlen == 0 ||
            (inlen % TC_AES_BLOCK_SIZE) != 0 ||
            (outlen % TC_AES_BLOCK_SIZE) != 0 ||
            outlen != inlen + TC_AES_BLOCK_SIZE)
    {
        return TC_CRYPTO_FAIL;
    }

    /* copy iv to the buffer */
    (void)_copy(buffer, TC_AES_BLOCK_SIZE, iv, TC_AES_BLOCK_SIZE);
    /* copy iv to the output buffer */
    (void)_copy(out, TC_AES_BLOCK_SIZE, iv, TC_AES_BLOCK_SIZE);
    out += TC_AES_BLOCK_SIZE;

    for (n = m = 0; n < inlen; ++n)
    {
        buffer[m++] ^= *in++;

        if (m == TC_AES_BLOCK_SIZE)
        {
            (void)tc_aes_encrypt(buffer, buffer, sched);
            (void)_copy(out, TC_AES_BLOCK_SIZE,
                        buffer, TC_AES_BLOCK_SIZE);
            out += TC_AES_BLOCK_SIZE;
            m = 0;
        }
    }

    return TC_CRYPTO_SUCCESS;
}

int tc_cbc_mode_decrypt(uint8_t* out, unsigned int outlen, const uint8_t* in,
                        unsigned int inlen, const uint8_t* iv,
                        const TCAesKeySched_t sched)
{
    uint8_t buffer[TC_AES_BLOCK_SIZE];
    const uint8_t* p;
    unsigned int n, m;

    /* sanity check the inputs */
    if (out == (uint8_t*) 0 ||
            in == (const uint8_t*) 0 ||
            sched == (TCAesKeySched_t) 0 ||
            inlen == 0 ||
            outlen == 0 ||
            (inlen % TC_AES_BLOCK_SIZE) != 0 ||
            (outlen % TC_AES_BLOCK_SIZE) != 0 ||
            outlen != inlen - TC_AES_BLOCK_SIZE)
    {
        return TC_CRYPTO_FAIL;
    }

    /*
        Note that in == iv + ciphertext, i.e. the iv and the ciphertext are
        contiguous. This allows for a very efficient decryption algorithm
        that would not otherwise be possible.
    */
    p = iv;

    for (n = m = 0; n < inlen; ++n)
    {
        if ((n % TC_AES_BLOCK_SIZE) == 0)
        {
            (void)tc_aes_decrypt(buffer, in, sched);
            in += TC_AES_BLOCK_SIZE;
            m = 0;
        }

        *out++ = buffer[m++] ^ *p++;
    }

    return TC_CRYPTO_SUCCESS;
}
