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
77 */
update(TCHmacPrng_t prng,const uint8_t * data,unsigned int datalen,const uint8_t * additional_data,unsigned int additional_datalen)78 static void update(TCHmacPrng_t prng, const uint8_t *data, unsigned int datalen, const uint8_t *additional_data, unsigned int additional_datalen)
79 {
80 const uint8_t separator0 = 0x00;
81 const uint8_t separator1 = 0x01;
82
83 /* configure the new prng key into the prng's instance of hmac */
84 tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
85
86 /* use current state, e and separator 0 to compute a new prng key: */
87 (void)tc_hmac_init(&prng->h);
88 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
89 (void)tc_hmac_update(&prng->h, &separator0, sizeof(separator0));
90
91 if (data && datalen) {
92 (void)tc_hmac_update(&prng->h, data, datalen);
93 }
94 if (additional_data && additional_datalen) {
95 (void)tc_hmac_update(&prng->h, additional_data, additional_datalen);
96 }
97
98 (void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
99
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
103 /* use the new key to compute a new state variable v */
104 (void)tc_hmac_init(&prng->h);
105 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
106 (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
107
108 if (data == 0 || datalen == 0) {
109 return;
110 }
111
112 /* configure the new prng key into the prng's instance of hmac */
113 tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
114
115 /* use current state, e and separator 1 to compute a new prng key: */
116 (void)tc_hmac_init(&prng->h);
117 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
118 (void)tc_hmac_update(&prng->h, &separator1, sizeof(separator1));
119 (void)tc_hmac_update(&prng->h, data, datalen);
120 if (additional_data && additional_datalen) {
121 (void)tc_hmac_update(&prng->h, additional_data, additional_datalen);
122 }
123 (void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
124
125 /* configure the new prng key into the prng's instance of hmac */
126 (void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
127
128 /* use the new key to compute a new state variable v */
129 (void)tc_hmac_init(&prng->h);
130 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
131 (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
132 }
133
tc_hmac_prng_init(TCHmacPrng_t prng,const uint8_t * personalization,unsigned int plen)134 int tc_hmac_prng_init(TCHmacPrng_t prng,
135 const uint8_t *personalization,
136 unsigned int plen)
137 {
138
139 /* input sanity check: */
140 if (prng == (TCHmacPrng_t) 0 ||
141 personalization == (uint8_t *) 0 ||
142 plen > MAX_PLEN) {
143 return TC_CRYPTO_FAIL;
144 }
145
146 /* put the generator into a known state: */
147 _set(prng->key, 0x00, sizeof(prng->key));
148 _set(prng->v, 0x01, sizeof(prng->v));
149
150 update(prng, personalization, plen, 0, 0);
151
152 /* force a reseed before allowing tc_hmac_prng_generate to succeed: */
153 prng->countdown = 0;
154
155 return TC_CRYPTO_SUCCESS;
156 }
157
tc_hmac_prng_reseed(TCHmacPrng_t prng,const uint8_t * seed,unsigned int seedlen,const uint8_t * additional_input,unsigned int additionallen)158 int tc_hmac_prng_reseed(TCHmacPrng_t prng,
159 const uint8_t *seed,
160 unsigned int seedlen,
161 const uint8_t *additional_input,
162 unsigned int additionallen)
163 {
164
165 /* input sanity check: */
166 if (prng == (TCHmacPrng_t) 0 ||
167 seed == (const uint8_t *) 0 ||
168 seedlen < MIN_SLEN ||
169 seedlen > MAX_SLEN) {
170 return TC_CRYPTO_FAIL;
171 }
172
173 if (additional_input != (const uint8_t *) 0) {
174 /*
175 * Abort if additional_input is provided but has inappropriate
176 * length
177 */
178 if (additionallen == 0 ||
179 additionallen > MAX_ALEN) {
180 return TC_CRYPTO_FAIL;
181 } else {
182 /* call update for the seed and additional_input */
183 update(prng, seed, seedlen, additional_input, additionallen);
184 }
185 } else {
186 /* call update only for the seed */
187 update(prng, seed, seedlen, 0, 0);
188 }
189
190 /* ... and enable hmac_prng_generate */
191 prng->countdown = MAX_GENS;
192
193 return TC_CRYPTO_SUCCESS;
194 }
195
tc_hmac_prng_generate(uint8_t * out,unsigned int outlen,TCHmacPrng_t prng)196 int tc_hmac_prng_generate(uint8_t *out, unsigned int outlen, TCHmacPrng_t prng)
197 {
198 unsigned int bufferlen;
199
200 /* input sanity check: */
201 if (out == (uint8_t *) 0 ||
202 prng == (TCHmacPrng_t) 0 ||
203 outlen == 0 ||
204 outlen > MAX_OUT) {
205 return TC_CRYPTO_FAIL;
206 } else if (prng->countdown == 0) {
207 return TC_HMAC_PRNG_RESEED_REQ;
208 }
209
210 prng->countdown--;
211
212 while (outlen != 0) {
213 /* configure the new prng key into the prng's instance of hmac */
214 tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
215
216 /* operate HMAC in OFB mode to create "random" outputs */
217 (void)tc_hmac_init(&prng->h);
218 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
219 (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
220
221 bufferlen = (TC_SHA256_DIGEST_SIZE > outlen) ?
222 outlen : TC_SHA256_DIGEST_SIZE;
223 (void)_copy(out, bufferlen, prng->v, bufferlen);
224
225 out += bufferlen;
226 outlen = (outlen > TC_SHA256_DIGEST_SIZE) ?
227 (outlen - TC_SHA256_DIGEST_SIZE) : 0;
228 }
229
230 /* block future PRNG compromises from revealing past state */
231 update(prng, 0, 0, 0, 0);
232
233 return TC_CRYPTO_SUCCESS;
234 }
235
