/* 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) {
        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 < outlen; ++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;
}
