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/* hmac_prng.c - TinyCrypt implementation of HMAC-PRNG */
/*
* Copyright (C) 2015 by Intel Corporation, All Rights Reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* - Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Intel Corporation nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <tinycrypt/hmac_prng.h>
#include <tinycrypt/hmac.h>
#include <tinycrypt/constants.h>
#include <tinycrypt/utils.h>
/*
* min bytes in the seed string.
* MIN_SLEN*8 must be at least the expected security level.
*/
static const uint32_t MIN_SLEN = 32;
/*
* max bytes in the seed string;
* SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
*/
static const uint32_t MAX_SLEN = UINT32_MAX;
/*
* max bytes in the personalization string;
* SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
*/
static const uint32_t MAX_PLEN = UINT32_MAX;
/*
* max bytes in the additional_info string;
* SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
*/
static const uint32_t MAX_ALEN = UINT32_MAX;
/*
* max number of generates between re-seeds;
* TinyCrypt accepts up to (2^32 - 1) which is the maximal value of
* a uint32_t variable, while SP800-90A specifies a maximum of 2^48.
*/
static const uint32_t MAX_GENS = UINT32_MAX;
/*
* maximum bytes per generate call;
* SP800-90A specifies a maximum up to 2^19.
*/
static const uint32_t MAX_OUT = (1 << 19);
/*
* Assumes: prng != NULL, e != NULL, len >= 0.
*/
static void update(TCHmacPrng_t prng, const uint8_t *e, uint32_t len)
{
const uint8_t separator0 = 0x00;
const uint8_t separator1 = 0x01;
/* use current state, e and separator 0 to compute a new prng key: */
(void)tc_hmac_init(&prng->h);
(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
(void)tc_hmac_update(&prng->h, &separator0, sizeof(separator0));
(void)tc_hmac_update(&prng->h, e, len);
(void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
/* configure the new prng key into the prng's instance of hmac */
(void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
/* use the new key to compute a new state variable v */
(void)tc_hmac_init(&prng->h);
(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
(void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
/* use current state, e and separator 1 to compute a new prng key: */
(void)tc_hmac_init(&prng->h);
(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
(void)tc_hmac_update(&prng->h, &separator1, sizeof(separator1));
(void)tc_hmac_update(&prng->h, e, len);
(void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
/* configure the new prng key into the prng's instance of hmac */
(void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
/* use the new key to compute a new state variable v */
(void)tc_hmac_init(&prng->h);
(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
(void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
}
int32_t tc_hmac_prng_init(TCHmacPrng_t prng,
const uint8_t *personalization,
uint32_t plen)
{
/* input sanity check: */
if (prng == (TCHmacPrng_t) 0 ||
personalization == (uint8_t *) 0 ||
plen > MAX_PLEN) {
return TC_CRYPTO_FAIL;
}
/* put the generator into a known state: */
_set(prng->key, 0x00, sizeof(prng->key));
_set(prng->v, 0x01, sizeof(prng->v));
tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
/* update assumes SOME key has been configured into HMAC */
update(prng, personalization, plen);
/* force a reseed before allowing tc_hmac_prng_generate to succeed: */
prng->countdown = 0;
return TC_CRYPTO_SUCCESS;
}
int32_t tc_hmac_prng_reseed(TCHmacPrng_t prng,
const uint8_t *seed,
uint32_t seedlen,
const uint8_t *additional_input,
uint32_t additionallen)
{
/* input sanity check: */
if (prng == (TCHmacPrng_t) 0 ||
seed == (const uint8_t *) 0 ||
seedlen < MIN_SLEN ||
seedlen > MAX_SLEN) {
return TC_CRYPTO_FAIL;
}
if (additional_input != (const uint8_t *) 0) {
/*
* Abort if additional_input is provided but has inappropriate
* length
*/
if (additionallen == 0 ||
additionallen > MAX_ALEN) {
return TC_CRYPTO_FAIL;
} else {
/* call update for the seed and additional_input */
update(prng, seed, seedlen);
update(prng, additional_input, additionallen);
}
} else {
/* call update only for the seed */
update(prng, seed, seedlen);
}
/* ... and enable hmac_prng_generate */
prng->countdown = MAX_GENS;
return TC_CRYPTO_SUCCESS;
}
int32_t tc_hmac_prng_generate(uint8_t *out, uint32_t outlen, TCHmacPrng_t prng)
{
uint32_t bufferlen;
/* input sanity check: */
if (out == (uint8_t *) 0 ||
prng == (TCHmacPrng_t) 0 ||
outlen == 0 ||
outlen > MAX_OUT) {
return TC_CRYPTO_FAIL;
} else if (prng->countdown == 0) {
return TC_HMAC_PRNG_RESEED_REQ;
}
prng->countdown--;
while (outlen != 0) {
/* operate HMAC in OFB mode to create "random" outputs */
(void)tc_hmac_init(&prng->h);
(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
(void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
bufferlen = (TC_SHA256_DIGEST_SIZE > outlen) ?
outlen : TC_SHA256_DIGEST_SIZE;
(void)_copy(out, bufferlen, prng->v, bufferlen);
out += bufferlen;
outlen = (outlen > TC_SHA256_DIGEST_SIZE) ?
(outlen - TC_SHA256_DIGEST_SIZE) : 0;
}
/* block future PRNG compromises from revealing past state */
update(prng, prng->v, TC_SHA256_DIGEST_SIZE);
return TC_CRYPTO_SUCCESS;
}
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