1 /* hmac_prng.c - TinyCrypt implementation of HMAC-PRNG */
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_prng.h>
34 #include <tinycrypt/hmac.h>
35 #include <tinycrypt/constants.h>
36 #include <tinycrypt/utils.h>
37
38 /*
39 * min bytes in the seed string.
40 * MIN_SLEN*8 must be at least the expected security level.
41 */
42 static const unsigned int MIN_SLEN = 32;
43
44 /*
45 * max bytes in the seed string;
46 * SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
47 */
48 static const unsigned int MAX_SLEN = UINT32_MAX;
49
50 /*
51 * max bytes in the personalization string;
52 * SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
53 */
54 static const unsigned int MAX_PLEN = UINT32_MAX;
55
56 /*
57 * max bytes in the additional_info string;
58 * SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
59 */
60 static const unsigned int MAX_ALEN = UINT32_MAX;
61
62 /*
63 * max number of generates between re-seeds;
64 * TinyCrypt accepts up to (2^32 - 1) which is the maximal value of
65 * a 32-bit unsigned int variable, while SP800-90A specifies a maximum of 2^48.
66 */
67 static const unsigned int MAX_GENS = UINT32_MAX;
68
69 /*
70 * maximum bytes per generate call;
71 * SP800-90A specifies a maximum up to 2^19.
72 */
73 static const unsigned int MAX_OUT = (1 << 19);
74
75 /*
76 * Assumes: prng != NULL, e != NULL, len >= 0.
77 */
update(TCHmacPrng_t prng,const uint8_t * e,unsigned int len)78 static void update(TCHmacPrng_t prng, const uint8_t *e, unsigned int len)
79 {
80 const uint8_t separator0 = 0x00;
81 const uint8_t separator1 = 0x01;
82 /* use current state, e and separator 0 to compute a new prng key: */
83 (void)tc_hmac_init(&prng->h);
84 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
85 (void)tc_hmac_update(&prng->h, &separator0, sizeof(separator0));
86 (void)tc_hmac_update(&prng->h, e, len);
87 (void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
88 /* configure the new prng key into the prng's instance of hmac */
89 (void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
90 /* use the new key to compute a new state variable v */
91 (void)tc_hmac_init(&prng->h);
92 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
93 (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
94 /* use current state, e and separator 1 to compute a new prng key: */
95 (void)tc_hmac_init(&prng->h);
96 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
97 (void)tc_hmac_update(&prng->h, &separator1, sizeof(separator1));
98 (void)tc_hmac_update(&prng->h, e, len);
99 (void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
100 /* configure the new prng key into the prng's instance of hmac */
101 (void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
102 /* use the new key to compute a new state variable v */
103 (void)tc_hmac_init(&prng->h);
104 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
105 (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
106 }
107
tc_hmac_prng_init(TCHmacPrng_t prng,const uint8_t * personalization,unsigned int plen)108 int tc_hmac_prng_init(TCHmacPrng_t prng,
109 const uint8_t *personalization,
110 unsigned int plen)
111 {
112 /* input sanity check: */
113 if (prng == (TCHmacPrng_t) 0 ||
114 personalization == (uint8_t *) 0 ||
115 plen > MAX_PLEN) {
116 return TC_CRYPTO_FAIL;
117 }
118
119 /* put the generator into a known state: */
120 _set(prng->key, 0x00, sizeof(prng->key));
121 _set(prng->v, 0x01, sizeof(prng->v));
122 tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
123 /* update assumes SOME key has been configured into HMAC */
124 update(prng, personalization, plen);
125 /* force a reseed before allowing tc_hmac_prng_generate to succeed: */
126 prng->countdown = 0;
127 return TC_CRYPTO_SUCCESS;
128 }
129
tc_hmac_prng_reseed(TCHmacPrng_t prng,const uint8_t * seed,unsigned int seedlen,const uint8_t * additional_input,unsigned int additionallen)130 int tc_hmac_prng_reseed(TCHmacPrng_t prng,
131 const uint8_t *seed,
132 unsigned int seedlen,
133 const uint8_t *additional_input,
134 unsigned int additionallen)
135 {
136 /* input sanity check: */
137 if (prng == (TCHmacPrng_t) 0 ||
138 seed == (const uint8_t *) 0 ||
139 seedlen < MIN_SLEN ||
140 seedlen > MAX_SLEN) {
141 return TC_CRYPTO_FAIL;
142 }
143
144 if (additional_input != (const uint8_t *) 0) {
145 /*
146 * Abort if additional_input is provided but has inappropriate
147 * length
148 */
149 if (additionallen == 0 ||
150 additionallen > MAX_ALEN) {
151 return TC_CRYPTO_FAIL;
152 } else {
153 /* call update for the seed and additional_input */
154 update(prng, seed, seedlen);
155 update(prng, additional_input, additionallen);
156 }
157 } else {
158 /* call update only for the seed */
159 update(prng, seed, seedlen);
160 }
161
162 /* ... and enable hmac_prng_generate */
163 prng->countdown = MAX_GENS;
164 return TC_CRYPTO_SUCCESS;
165 }
166
tc_hmac_prng_generate(uint8_t * out,unsigned int outlen,TCHmacPrng_t prng)167 int tc_hmac_prng_generate(uint8_t *out, unsigned int outlen, TCHmacPrng_t prng)
168 {
169 /* input sanity check: */
170 if (out == (uint8_t *) 0 ||
171 prng == (TCHmacPrng_t) 0 ||
172 outlen == 0 ||
173 outlen > MAX_OUT) {
174 return TC_CRYPTO_FAIL;
175 } else if (prng->countdown == 0) {
176 return TC_HMAC_PRNG_RESEED_REQ;
177 }
178
179 prng->countdown--;
180
181 while (outlen != 0) {
182 /* operate HMAC in OFB mode to create "random" outputs */
183 (void)tc_hmac_init(&prng->h);
184 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
185 (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
186 unsigned int bufferlen = (TC_SHA256_DIGEST_SIZE > outlen) ?
187 outlen : TC_SHA256_DIGEST_SIZE;
188 (void)_copy(out, bufferlen, prng->v, bufferlen);
189 out += bufferlen;
190 outlen = (outlen > TC_SHA256_DIGEST_SIZE) ?
191 (outlen - TC_SHA256_DIGEST_SIZE) : 0;
192 }
193
194 /* block future PRNG compromises from revealing past state */
195 update(prng, prng->v, TC_SHA256_DIGEST_SIZE);
196 return TC_CRYPTO_SUCCESS;
197 }