_ Git - BearSSL/blob - src/rand/hmac_drbg.c

   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
  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
  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
  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 };