1 /* hmac.c - TinyCrypt implementation of the HMAC algorithm */
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/hmac.h>
34 #include <tinycrypt/constants.h>
35 #include <tinycrypt/utils.h>
36
rekey(uint8_t * key,const uint8_t * new_key,unsigned int key_size)37 static void rekey(uint8_t *key, const uint8_t *new_key, unsigned int key_size)
38 {
39 const uint8_t inner_pad = (uint8_t) 0x36;
40 const uint8_t outer_pad = (uint8_t) 0x5c;
41 unsigned int i;
42
43 for (i = 0; i < key_size; ++i) {
44 key[i] = inner_pad ^ new_key[i];
45 key[i + TC_SHA256_BLOCK_SIZE] = outer_pad ^ new_key[i];
46 }
47 for (; i < TC_SHA256_BLOCK_SIZE; ++i) {
48 key[i] = inner_pad; key[i + TC_SHA256_BLOCK_SIZE] = outer_pad;
49 }
50 }
51
tc_hmac_set_key(TCHmacState_t ctx,const uint8_t * key,unsigned int key_size)52 int tc_hmac_set_key(TCHmacState_t ctx, const uint8_t *key,
53 unsigned int key_size)
54 {
55 /* Input sanity check */
56 if (ctx == (TCHmacState_t) 0 ||
57 key == (const uint8_t *) 0 ||
58 key_size == 0) {
59 return TC_CRYPTO_FAIL;
60 }
61
62 const uint8_t dummy_key[TC_SHA256_BLOCK_SIZE];
63 struct tc_hmac_state_struct dummy_state;
64
65 if (key_size <= TC_SHA256_BLOCK_SIZE) {
66 /*
67 * The next three calls are dummy calls just to avoid
68 * certain timing attacks. Without these dummy calls,
69 * adversaries would be able to learn whether the key_size is
70 * greater than TC_SHA256_BLOCK_SIZE by measuring the time
71 * consumed in this process.
72 */
73 (void)tc_sha256_init(&dummy_state.hash_state);
74 (void)tc_sha256_update(&dummy_state.hash_state,
75 dummy_key,
76 key_size);
77 (void)tc_sha256_final(&dummy_state.key[TC_SHA256_DIGEST_SIZE],
78 &dummy_state.hash_state);
79
80 /* Actual code for when key_size <= TC_SHA256_BLOCK_SIZE: */
81 rekey(ctx->key, key, key_size);
82 } else {
83 (void)tc_sha256_init(&ctx->hash_state);
84 (void)tc_sha256_update(&ctx->hash_state, key, key_size);
85 (void)tc_sha256_final(&ctx->key[TC_SHA256_DIGEST_SIZE],
86 &ctx->hash_state);
87 rekey(ctx->key,
88 &ctx->key[TC_SHA256_DIGEST_SIZE],
89 TC_SHA256_DIGEST_SIZE);
90 }
91
92 return TC_CRYPTO_SUCCESS;
93 }
94
tc_hmac_init(TCHmacState_t ctx)95 int tc_hmac_init(TCHmacState_t ctx)
96 {
97
98 /* input sanity check: */
99 if (ctx == (TCHmacState_t) 0) {
100 return TC_CRYPTO_FAIL;
101 }
102
103 (void) tc_sha256_init(&ctx->hash_state);
104 (void) tc_sha256_update(&ctx->hash_state, ctx->key, TC_SHA256_BLOCK_SIZE);
105
106 return TC_CRYPTO_SUCCESS;
107 }
108
tc_hmac_update(TCHmacState_t ctx,const void * data,unsigned int data_length)109 int tc_hmac_update(TCHmacState_t ctx,
110 const void *data,
111 unsigned int data_length)
112 {
113
114 /* input sanity check: */
115 if (ctx == (TCHmacState_t) 0) {
116 return TC_CRYPTO_FAIL;
117 }
118
119 (void)tc_sha256_update(&ctx->hash_state, data, data_length);
120
121 return TC_CRYPTO_SUCCESS;
122 }
123
tc_hmac_final(uint8_t * tag,unsigned int taglen,TCHmacState_t ctx)124 int tc_hmac_final(uint8_t *tag, unsigned int taglen, TCHmacState_t ctx)
125 {
126
127 /* input sanity check: */
128 if (tag == (uint8_t *) 0 ||
129 taglen != TC_SHA256_DIGEST_SIZE ||
130 ctx == (TCHmacState_t) 0) {
131 return TC_CRYPTO_FAIL;
132 }
133
134 (void) tc_sha256_final(tag, &ctx->hash_state);
135
136 (void)tc_sha256_init(&ctx->hash_state);
137 (void)tc_sha256_update(&ctx->hash_state,
138 &ctx->key[TC_SHA256_BLOCK_SIZE],
139 TC_SHA256_BLOCK_SIZE);
140 (void)tc_sha256_update(&ctx->hash_state, tag, TC_SHA256_DIGEST_SIZE);
141 (void)tc_sha256_final(tag, &ctx->hash_state);
142
143 /* destroy the current state */
144 _set(ctx, 0, sizeof(*ctx));
145
146 return TC_CRYPTO_SUCCESS;
147 }
148