1 /* ctr_mode.c - TinyCrypt CTR mode implementation */
2
3 /*
4 * Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions are met:
8 *
9 * - Redistributions of source code must retain the above copyright notice,
10 * this list of conditions and the following disclaimer.
11 *
12 * - Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * - Neither the name of Intel Corporation nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
18 * without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
21 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
24 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
25 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
26 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
27 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
28 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
29 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
30 * POSSIBILITY OF SUCH DAMAGE.
31 */
32
33 #include <tinycrypt/constants.h>
34 #include <tinycrypt/ctr_mode.h>
35 #include <tinycrypt/utils.h>
36
tc_ctr_mode(uint8_t * out,unsigned int outlen,const uint8_t * in,unsigned int inlen,uint8_t * ctr,const TCAesKeySched_t sched)37 int tc_ctr_mode(uint8_t *out, unsigned int outlen, const uint8_t *in,
38 unsigned int inlen, uint8_t *ctr, const TCAesKeySched_t sched)
39 {
40
41 uint8_t buffer[TC_AES_BLOCK_SIZE];
42 uint8_t nonce[TC_AES_BLOCK_SIZE];
43 unsigned int block_num;
44 unsigned int i;
45
46 /* input sanity check: */
47 if (out == (uint8_t *) 0 ||
48 in == (uint8_t *) 0 ||
49 ctr == (uint8_t *) 0 ||
50 sched == (TCAesKeySched_t) 0 ||
51 inlen == 0 ||
52 outlen == 0 ||
53 outlen != inlen) {
54 return TC_CRYPTO_FAIL;
55 }
56
57 /* copy the ctr to the nonce */
58 (void)_copy(nonce, sizeof(nonce), ctr, sizeof(nonce));
59
60 /* select the last 4 bytes of the nonce to be incremented */
61 block_num = (nonce[12] << 24) | (nonce[13] << 16) |
62 (nonce[14] << 8) | (nonce[15]);
63 for (i = 0; i < inlen; ++i) {
64 if ((i % (TC_AES_BLOCK_SIZE)) == 0) {
65 /* encrypt data using the current nonce */
66 if (tc_aes_encrypt(buffer, nonce, sched)) {
67 block_num++;
68 nonce[12] = (uint8_t)(block_num >> 24);
69 nonce[13] = (uint8_t)(block_num >> 16);
70 nonce[14] = (uint8_t)(block_num >> 8);
71 nonce[15] = (uint8_t)(block_num);
72 } else {
73 return TC_CRYPTO_FAIL;
74 }
75 }
76 /* update the output */
77 *out++ = buffer[i % (TC_AES_BLOCK_SIZE)] ^ *in++;
78 }
79
80 /* update the counter */
81 ctr[12] = nonce[12]; ctr[13] = nonce[13];
82 ctr[14] = nonce[14]; ctr[15] = nonce[15];
83
84 return TC_CRYPTO_SUCCESS;
85 }
86
