1 /*
2 * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 * SOFTWARE.
23 */
24
25 #include "inner.h"
26
27 /* see bearssl.h */
28 void
br_hmac_drbg_init(br_hmac_drbg_context * ctx,const br_hash_class * digest_class,const void * seed,size_t len)29 br_hmac_drbg_init(br_hmac_drbg_context *ctx,
30 const br_hash_class *digest_class, const void *seed, size_t len)
31 {
32 size_t hlen;
33
34 ctx->vtable = &br_hmac_drbg_vtable;
35 hlen = br_digest_size(digest_class);
36 memset(ctx->K, 0x00, hlen);
37 memset(ctx->V, 0x01, hlen);
38 ctx->digest_class = digest_class;
39 br_hmac_drbg_update(ctx, seed, len);
40 }
41
42 /* see bearssl.h */
43 void
br_hmac_drbg_generate(br_hmac_drbg_context * ctx,void * out,size_t len)44 br_hmac_drbg_generate(br_hmac_drbg_context *ctx, void *out, size_t len)
45 {
46 const br_hash_class *dig;
47 br_hmac_key_context kc;
48 br_hmac_context hc;
49 size_t hlen;
50 unsigned char *buf;
51 unsigned char x;
52
53 dig = ctx->digest_class;
54 hlen = br_digest_size(dig);
55 br_hmac_key_init(&kc, dig, ctx->K, hlen);
56 buf = out;
57 while (len > 0) {
58 size_t clen;
59
60 br_hmac_init(&hc, &kc, 0);
61 br_hmac_update(&hc, ctx->V, hlen);
62 br_hmac_out(&hc, ctx->V);
63 clen = hlen;
64 if (clen > len) {
65 clen = len;
66 }
67 memcpy(buf, ctx->V, clen);
68 buf += clen;
69 len -= clen;
70 }
71
72 /*
73 * To prepare the state for the next request, we should call
74 * br_hmac_drbg_update() with an empty additional seed. However,
75 * we already have an initialized HMAC context with the right
76 * initial key, and we don't want to push another one on the
77 * stack, so we inline that update() call here.
78 */
79 br_hmac_init(&hc, &kc, 0);
80 br_hmac_update(&hc, ctx->V, hlen);
81 x = 0x00;
82 br_hmac_update(&hc, &x, 1);
83 br_hmac_out(&hc, ctx->K);
84 br_hmac_key_init(&kc, dig, ctx->K, hlen);
85 br_hmac_init(&hc, &kc, 0);
86 br_hmac_update(&hc, ctx->V, hlen);
87 br_hmac_out(&hc, ctx->V);
88 }
89
90 /* see bearssl.h */
91 void
br_hmac_drbg_update(br_hmac_drbg_context * ctx,const void * seed,size_t len)92 br_hmac_drbg_update(br_hmac_drbg_context *ctx, const void *seed, size_t len)
93 {
94 const br_hash_class *dig;
95 br_hmac_key_context kc;
96 br_hmac_context hc;
97 size_t hlen;
98 unsigned char x;
99
100 dig = ctx->digest_class;
101 hlen = br_digest_size(dig);
102
103 /*
104 * 1. K = HMAC(K, V || 0x00 || seed)
105 */
106 br_hmac_key_init(&kc, dig, ctx->K, hlen);
107 br_hmac_init(&hc, &kc, 0);
108 br_hmac_update(&hc, ctx->V, hlen);
109 x = 0x00;
110 br_hmac_update(&hc, &x, 1);
111 br_hmac_update(&hc, seed, len);
112 br_hmac_out(&hc, ctx->K);
113 br_hmac_key_init(&kc, dig, ctx->K, hlen);
114
115 /*
116 * 2. V = HMAC(K, V)
117 */
118 br_hmac_init(&hc, &kc, 0);
119 br_hmac_update(&hc, ctx->V, hlen);
120 br_hmac_out(&hc, ctx->V);
121
122 /*
123 * 3. If the additional seed is empty, then stop here.
124 */
125 if (len == 0) {
126 return;
127 }
128
129 /*
130 * 4. K = HMAC(K, V || 0x01 || seed)
131 */
132 br_hmac_init(&hc, &kc, 0);
133 br_hmac_update(&hc, ctx->V, hlen);
134 x = 0x01;
135 br_hmac_update(&hc, &x, 1);
136 br_hmac_update(&hc, seed, len);
137 br_hmac_out(&hc, ctx->K);
138 br_hmac_key_init(&kc, dig, ctx->K, hlen);
139
140 /*
141 * 5. V = HMAC(K, V)
142 */
143 br_hmac_init(&hc, &kc, 0);
144 br_hmac_update(&hc, ctx->V, hlen);
145 br_hmac_out(&hc, ctx->V);
146 }
147
148 /* see bearssl.h */
149 const br_prng_class br_hmac_drbg_vtable = {
150 sizeof(br_hmac_drbg_context),
151 (void (*)(const br_prng_class **, const void *, const void *, size_t))
152 &br_hmac_drbg_init,
153 (void (*)(const br_prng_class **, void *, size_t))
154 &br_hmac_drbg_generate,
155 (void (*)(const br_prng_class **, const void *, size_t))
156 &br_hmac_drbg_update
157 };
158