/* ctr_mode.c - TinyCrypt CTR mode implementation */

/*
 *  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
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 *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *  POSSIBILITY OF SUCH DAMAGE.
 */

#include <tinycrypt/constants.h>
#include <tinycrypt/ctr_mode.h>
#include <tinycrypt/utils.h>

int tc_ctr_mode(uint8_t *out, unsigned int outlen, const uint8_t *in,
                unsigned int inlen, uint8_t *ctr, const TCAesKeySched_t sched)
{

    uint8_t buffer[TC_AES_BLOCK_SIZE];
    uint8_t nonce[TC_AES_BLOCK_SIZE];
    unsigned int block_num;
    unsigned int i;

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

    /* copy the ctr to the nonce */
    (void)_copy(nonce, sizeof(nonce), ctr, sizeof(nonce));

    /* select the last 4 bytes of the nonce to be incremented */
    block_num = (nonce[12] << 24) | (nonce[13] << 16) |
                (nonce[14] << 8) | (nonce[15]);
    for (i = 0; i < inlen; ++i) {
        if ((i % (TC_AES_BLOCK_SIZE)) == 0) {
            /* encrypt data using the current nonce */
            if (tc_aes_encrypt(buffer, nonce, sched)) {
                block_num++;
                nonce[12] = (uint8_t)(block_num >> 24);
                nonce[13] = (uint8_t)(block_num >> 16);
                nonce[14] = (uint8_t)(block_num >> 8);
                nonce[15] = (uint8_t)(block_num);
            } else {
                return TC_CRYPTO_FAIL;
            }
        }
        /* update the output */
        *out++ = buffer[i % (TC_AES_BLOCK_SIZE)] ^ *in++;
    }

    /* update the counter */
    ctr[12] = nonce[12]; ctr[13] = nonce[13];
    ctr[14] = nonce[14]; ctr[15] = nonce[15];

    return TC_CRYPTO_SUCCESS;
}
