/* cbc_mode.c - TinyCrypt implementation of CBC mode encryption & decryption */
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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/cbc_mode.h>
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#include <tinycrypt/constants.h>
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#include <tinycrypt/utils.h>
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int tc_cbc_mode_encrypt(uint8_t *out, unsigned int outlen, const uint8_t *in,
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unsigned int inlen, const uint8_t *iv,
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const TCAesKeySched_t sched)
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{
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uint8_t buffer[TC_AES_BLOCK_SIZE];
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unsigned int n, m;
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/* input sanity check: */
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if (out == (uint8_t *) 0 ||
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in == (const 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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(inlen % TC_AES_BLOCK_SIZE) != 0 ||
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(outlen % TC_AES_BLOCK_SIZE) != 0 ||
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outlen != inlen + TC_AES_BLOCK_SIZE) {
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return TC_CRYPTO_FAIL;
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}
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/* copy iv to the buffer */
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(void)_copy(buffer, TC_AES_BLOCK_SIZE, iv, TC_AES_BLOCK_SIZE);
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/* copy iv to the output buffer */
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(void)_copy(out, TC_AES_BLOCK_SIZE, iv, TC_AES_BLOCK_SIZE);
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out += TC_AES_BLOCK_SIZE;
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for (n = m = 0; n < inlen; ++n) {
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buffer[m++] ^= *in++;
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if (m == TC_AES_BLOCK_SIZE) {
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(void)tc_aes_encrypt(buffer, buffer, sched);
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(void)_copy(out, TC_AES_BLOCK_SIZE,
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buffer, TC_AES_BLOCK_SIZE);
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out += TC_AES_BLOCK_SIZE;
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m = 0;
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}
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}
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return TC_CRYPTO_SUCCESS;
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}
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int tc_cbc_mode_decrypt(uint8_t *out, unsigned int outlen, const uint8_t *in,
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unsigned int inlen, const uint8_t *iv,
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const TCAesKeySched_t sched)
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{
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uint8_t buffer[TC_AES_BLOCK_SIZE];
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const uint8_t *p;
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unsigned int n, m;
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/* sanity check the inputs */
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if (out == (uint8_t *) 0 ||
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in == (const 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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(inlen % TC_AES_BLOCK_SIZE) != 0 ||
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(outlen % TC_AES_BLOCK_SIZE) != 0 ||
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outlen != inlen - TC_AES_BLOCK_SIZE) {
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return TC_CRYPTO_FAIL;
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}
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/*
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* Note that in == iv + ciphertext, i.e. the iv and the ciphertext are
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* contiguous. This allows for a very efficient decryption algorithm
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* that would not otherwise be possible.
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*/
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p = iv;
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for (n = m = 0; n < inlen; ++n) {
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if ((n % TC_AES_BLOCK_SIZE) == 0) {
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(void)tc_aes_decrypt(buffer, in, sched);
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in += TC_AES_BLOCK_SIZE;
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m = 0;
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}
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*out++ = buffer[m++] ^ *p++;
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}
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return TC_CRYPTO_SUCCESS;
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}
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