/*
* Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "inner.h"
/* see bearssl.h */
void
br_hmac_drbg_init(br_hmac_drbg_context *ctx,
const br_hash_class *digest_class, const void *seed, size_t len)
{
size_t hlen;
ctx->vtable = &br_hmac_drbg_vtable;
hlen = br_digest_size(digest_class);
memset(ctx->K, 0x00, hlen);
memset(ctx->V, 0x01, hlen);
ctx->digest_class = digest_class;
br_hmac_drbg_update(ctx, seed, len);
}
/* see bearssl.h */
void
br_hmac_drbg_generate(br_hmac_drbg_context *ctx, void *out, size_t len)
{
const br_hash_class *dig;
br_hmac_key_context kc;
br_hmac_context hc;
size_t hlen;
unsigned char *buf;
unsigned char x;
dig = ctx->digest_class;
hlen = br_digest_size(dig);
br_hmac_key_init(&kc, dig, ctx->K, hlen);
buf = out;
while (len > 0) {
size_t clen;
br_hmac_init(&hc, &kc, 0);
br_hmac_update(&hc, ctx->V, hlen);
br_hmac_out(&hc, ctx->V);
clen = hlen;
if (clen > len) {
clen = len;
}
memcpy(buf, ctx->V, clen);
buf += clen;
len -= clen;
}
/*
* To prepare the state for the next request, we should call
* br_hmac_drbg_update() with an empty additional seed. However,
* we already have an initialized HMAC context with the right
* initial key, and we don't want to push another one on the
* stack, so we inline that update() call here.
*/
br_hmac_init(&hc, &kc, 0);
br_hmac_update(&hc, ctx->V, hlen);
x = 0x00;
br_hmac_update(&hc, &x, 1);
br_hmac_out(&hc, ctx->K);
br_hmac_key_init(&kc, dig, ctx->K, hlen);
br_hmac_init(&hc, &kc, 0);
br_hmac_update(&hc, ctx->V, hlen);
br_hmac_out(&hc, ctx->V);
}
/* see bearssl.h */
void
br_hmac_drbg_update(br_hmac_drbg_context *ctx, const void *seed, size_t len)
{
const br_hash_class *dig;
br_hmac_key_context kc;
br_hmac_context hc;
size_t hlen;
unsigned char x;
dig = ctx->digest_class;
hlen = br_digest_size(dig);
/*
* 1. K = HMAC(K, V || 0x00 || seed)
*/
br_hmac_key_init(&kc, dig, ctx->K, hlen);
br_hmac_init(&hc, &kc, 0);
br_hmac_update(&hc, ctx->V, hlen);
x = 0x00;
br_hmac_update(&hc, &x, 1);
br_hmac_update(&hc, seed, len);
br_hmac_out(&hc, ctx->K);
br_hmac_key_init(&kc, dig, ctx->K, hlen);
/*
* 2. V = HMAC(K, V)
*/
br_hmac_init(&hc, &kc, 0);
br_hmac_update(&hc, ctx->V, hlen);
br_hmac_out(&hc, ctx->V);
/*
* 3. If the additional seed is empty, then stop here.
*/
if (len == 0) {
return;
}
/*
* 4. K = HMAC(K, V || 0x01 || seed)
*/
br_hmac_init(&hc, &kc, 0);
br_hmac_update(&hc, ctx->V, hlen);
x = 0x01;
br_hmac_update(&hc, &x, 1);
br_hmac_update(&hc, seed, len);
br_hmac_out(&hc, ctx->K);
br_hmac_key_init(&kc, dig, ctx->K, hlen);
/*
* 5. V = HMAC(K, V)
*/
br_hmac_init(&hc, &kc, 0);
br_hmac_update(&hc, ctx->V, hlen);
br_hmac_out(&hc, ctx->V);
}
/* see bearssl.h */
const br_prng_class br_hmac_drbg_vtable = {
sizeof(br_hmac_drbg_context),
(void (*)(const br_prng_class **, const void *, const void *, size_t))
&br_hmac_drbg_init,
(void (*)(const br_prng_class **, void *, size_t))
&br_hmac_drbg_generate,
(void (*)(const br_prng_class **, const void *, size_t))
&br_hmac_drbg_update
};