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 uint8_t buffer[TC_AES_BLOCK_SIZE];
41 uint8_t nonce[TC_AES_BLOCK_SIZE];
42 unsigned int block_num;
43 unsigned int i;
44
45 /* input sanity check: */
46 if (out == (uint8_t *) 0 ||
47 in == (uint8_t *) 0 ||
48 ctr == (uint8_t *) 0 ||
49 sched == (TCAesKeySched_t) 0 ||
50 inlen == 0 ||
51 outlen == 0 ||
52 outlen != inlen) {
53 return TC_CRYPTO_FAIL;
54 }
55
56 /* copy the ctr to the nonce */
57 (void)_copy(nonce, sizeof(nonce), ctr, sizeof(nonce));
58 /* select the last 4 bytes of the nonce to be incremented */
59 // 12:array element, 24:byte alignment, 13:array element, 16:byte alignment
60 block_num = (nonce[12] << 24) | (nonce[13] << 16) |
61 (nonce[14] << 8) | (nonce[15]); // 14:array element, 8:byte alignment, 15:array element
62
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); // 24:byte alignment, 12:array element
69 nonce[13] = (uint8_t)(block_num >> 16); // 16:byte alignment, 13:array element
70 nonce[14] = (uint8_t)(block_num >> 8); // 8:byte alignment, 14:array element
71 nonce[15] = (uint8_t)(block_num); // 15:array element
72 } else {
73 return TC_CRYPTO_FAIL;
74 }
75 }
76
77 /* update the output */
78 *out++ = buffer[i % (TC_AES_BLOCK_SIZE)] ^ *in++;
79 }
80
81 /* update the counter */
82 ctr[12] = nonce[12]; // 12:array element
83 ctr[13] = nonce[13]; // 13:array element
84 ctr[14] = nonce[14]; // 14:array element
85 ctr[15] = nonce[15]; // 15:array element
86 return TC_CRYPTO_SUCCESS;
87 }