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