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 if (additional_data && additional_datalen)
94 (void)tc_hmac_update(&prng->h, additional_data, additional_datalen);
95
96 (void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
97
98 /* configure the new prng key into the prng's instance of hmac */
99 (void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
100
101 /* use the new key to compute a new state variable v */
102 (void)tc_hmac_init(&prng->h);
103 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
104 (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
105
106 if (data == 0 || datalen == 0)
107 return;
108
109 /* configure the new prng key into the prng's instance of hmac */
110 tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
111
112 /* use current state, e and separator 1 to compute a new prng key: */
113 (void)tc_hmac_init(&prng->h);
114 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
115 (void)tc_hmac_update(&prng->h, &separator1, sizeof(separator1));
116 (void)tc_hmac_update(&prng->h, data, datalen);
117 if (additional_data && additional_datalen)
118 (void)tc_hmac_update(&prng->h, additional_data, additional_datalen);
119 (void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
120
121 /* configure the new prng key into the prng's instance of hmac */
122 (void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
123
124 /* use the new key to compute a new state variable v */
125 (void)tc_hmac_init(&prng->h);
126 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
127 (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
128 }
129
tc_hmac_prng_init(TCHmacPrng_t prng,const uint8_t * personalization,unsigned int plen)130 int tc_hmac_prng_init(TCHmacPrng_t prng,
131 const uint8_t *personalization,
132 unsigned int plen)
133 {
134
135 /* input sanity check: */
136 if (prng == (TCHmacPrng_t) 0 ||
137 personalization == (uint8_t *) 0 ||
138 plen > MAX_PLEN) {
139 return TC_CRYPTO_FAIL;
140 }
141
142 /* put the generator into a known state: */
143 _set(prng->key, 0x00, sizeof(prng->key));
144 _set(prng->v, 0x01, sizeof(prng->v));
145
146 update(prng, personalization, plen, 0, 0);
147
148 /* force a reseed before allowing tc_hmac_prng_generate to succeed: */
149 prng->countdown = 0;
150
151 return TC_CRYPTO_SUCCESS;
152 }
153
tc_hmac_prng_reseed(TCHmacPrng_t prng,const uint8_t * seed,unsigned int seedlen,const uint8_t * additional_input,unsigned int additionallen)154 int tc_hmac_prng_reseed(TCHmacPrng_t prng,
155 const uint8_t *seed,
156 unsigned int seedlen,
157 const uint8_t *additional_input,
158 unsigned int additionallen)
159 {
160
161 /* input sanity check: */
162 if (prng == (TCHmacPrng_t) 0 ||
163 seed == (const uint8_t *) 0 ||
164 seedlen < MIN_SLEN ||
165 seedlen > MAX_SLEN) {
166 return TC_CRYPTO_FAIL;
167 }
168
169 if (additional_input != (const uint8_t *) 0) {
170 /*
171 * Abort if additional_input is provided but has inappropriate
172 * length
173 */
174 if (additionallen == 0 ||
175 additionallen > MAX_ALEN) {
176 return TC_CRYPTO_FAIL;
177 } else {
178 /* call update for the seed and additional_input */
179 update(prng, seed, seedlen, additional_input, additionallen);
180 }
181 } else {
182 /* call update only for the seed */
183 update(prng, seed, seedlen, 0, 0);
184 }
185
186 /* ... and enable hmac_prng_generate */
187 prng->countdown = MAX_GENS;
188
189 return TC_CRYPTO_SUCCESS;
190 }
191
tc_hmac_prng_generate(uint8_t * out,unsigned int outlen,TCHmacPrng_t prng)192 int tc_hmac_prng_generate(uint8_t *out, unsigned int outlen, TCHmacPrng_t prng)
193 {
194 unsigned int bufferlen;
195
196 /* input sanity check: */
197 if (out == (uint8_t *) 0 ||
198 prng == (TCHmacPrng_t) 0 ||
199 outlen == 0 ||
200 outlen > MAX_OUT) {
201 return TC_CRYPTO_FAIL;
202 } else if (prng->countdown == 0) {
203 return TC_HMAC_PRNG_RESEED_REQ;
204 }
205
206 prng->countdown--;
207
208 while (outlen != 0) {
209 /* configure the new prng key into the prng's instance of hmac */
210 tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
211
212 /* operate HMAC in OFB mode to create "random" outputs */
213 (void)tc_hmac_init(&prng->h);
214 (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
215 (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
216
217 bufferlen = (TC_SHA256_DIGEST_SIZE > outlen) ?
218 outlen : TC_SHA256_DIGEST_SIZE;
219 (void)_copy(out, bufferlen, prng->v, bufferlen);
220
221 out += bufferlen;
222 outlen = (outlen > TC_SHA256_DIGEST_SIZE) ?
223 (outlen - TC_SHA256_DIGEST_SIZE) : 0;
224 }
225
226 /* block future PRNG compromises from revealing past state */
227 update(prng, 0, 0, 0, 0);
228
229 return TC_CRYPTO_SUCCESS;
230 }
231
