/* ctr_mode.c - TinyCrypt CTR mode implementation */
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/*
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* Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* - Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* - Neither the name of Intel Corporation nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <tinycrypt/constants.h>
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#include <tinycrypt/ctr_mode.h>
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#include <tinycrypt/utils.h>
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int tc_ctr_mode(uint8_t *out, unsigned int outlen, const uint8_t *in,
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unsigned int inlen, uint8_t *ctr, const TCAesKeySched_t sched)
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{
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uint8_t buffer[TC_AES_BLOCK_SIZE];
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uint8_t nonce[TC_AES_BLOCK_SIZE];
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unsigned int block_num;
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unsigned int i;
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/* input sanity check: */
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if (out == (uint8_t *) 0 ||
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in == (uint8_t *) 0 ||
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ctr == (uint8_t *) 0 ||
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sched == (TCAesKeySched_t) 0 ||
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inlen == 0 ||
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outlen == 0 ||
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outlen != inlen) {
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return TC_CRYPTO_FAIL;
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}
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/* copy the ctr to the nonce */
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(void)_copy(nonce, sizeof(nonce), ctr, sizeof(nonce));
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/* select the last 4 bytes of the nonce to be incremented */
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block_num = (nonce[12] << 24) | (nonce[13] << 16) |
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(nonce[14] << 8) | (nonce[15]);
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for (i = 0; i < inlen; ++i) {
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if ((i % (TC_AES_BLOCK_SIZE)) == 0) {
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/* encrypt data using the current nonce */
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if (tc_aes_encrypt(buffer, nonce, sched)) {
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block_num++;
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nonce[12] = (uint8_t)(block_num >> 24);
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nonce[13] = (uint8_t)(block_num >> 16);
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nonce[14] = (uint8_t)(block_num >> 8);
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nonce[15] = (uint8_t)(block_num);
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} else {
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return TC_CRYPTO_FAIL;
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}
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}
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/* update the output */
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*out++ = buffer[i%(TC_AES_BLOCK_SIZE)] ^ *in++;
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}
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/* update the counter */
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ctr[12] = nonce[12]; ctr[13] = nonce[13];
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ctr[14] = nonce[14]; ctr[15] = nonce[15];
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return TC_CRYPTO_SUCCESS;
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}
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