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 }; 158