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213 lines
6.7 KiB
C
213 lines
6.7 KiB
C
/* hmac_prng.c - TinyCrypt implementation of HMAC-PRNG */
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/*
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* Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* - Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* - Neither the name of Intel Corporation nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <tinycrypt/hmac_prng.h>
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#include <tinycrypt/hmac.h>
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#include <tinycrypt/constants.h>
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#include <tinycrypt/utils.h>
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/*
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* min bytes in the seed string.
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* MIN_SLEN*8 must be at least the expected security level.
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*/
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static const unsigned int MIN_SLEN = 32;
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/*
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* max bytes in the seed string;
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* SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
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*/
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static const unsigned int MAX_SLEN = UINT32_MAX;
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/*
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* max bytes in the personalization string;
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* SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
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*/
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static const unsigned int MAX_PLEN = UINT32_MAX;
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/*
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* max bytes in the additional_info string;
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* SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
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*/
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static const unsigned int MAX_ALEN = UINT32_MAX;
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/*
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* max number of generates between re-seeds;
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* TinyCrypt accepts up to (2^32 - 1) which is the maximal value of
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* a 32-bit unsigned int variable, while SP800-90A specifies a maximum of 2^48.
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*/
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static const unsigned int MAX_GENS = UINT32_MAX;
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/*
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* maximum bytes per generate call;
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* SP800-90A specifies a maximum up to 2^19.
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*/
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static const unsigned int MAX_OUT = (1 << 19);
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/*
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* Assumes: prng != NULL, e != NULL, len >= 0.
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*/
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static void update(TCHmacPrng_t prng, const uint8_t *e, unsigned int len)
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{
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const uint8_t separator0 = 0x00;
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const uint8_t separator1 = 0x01;
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/* use current state, e and separator 0 to compute a new prng key: */
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(void)tc_hmac_init(&prng->h);
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(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
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(void)tc_hmac_update(&prng->h, &separator0, sizeof(separator0));
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(void)tc_hmac_update(&prng->h, e, len);
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(void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
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/* configure the new prng key into the prng's instance of hmac */
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(void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
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/* use the new key to compute a new state variable v */
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(void)tc_hmac_init(&prng->h);
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(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
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(void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
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/* use current state, e and separator 1 to compute a new prng key: */
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(void)tc_hmac_init(&prng->h);
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(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
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(void)tc_hmac_update(&prng->h, &separator1, sizeof(separator1));
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(void)tc_hmac_update(&prng->h, e, len);
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(void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);
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/* configure the new prng key into the prng's instance of hmac */
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(void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
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/* use the new key to compute a new state variable v */
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(void)tc_hmac_init(&prng->h);
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(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
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(void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
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}
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int tc_hmac_prng_init(TCHmacPrng_t prng,
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const uint8_t *personalization,
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unsigned int plen)
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{
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/* input sanity check: */
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if (prng == (TCHmacPrng_t) 0 ||
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personalization == (uint8_t *) 0 ||
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plen > MAX_PLEN) {
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return TC_CRYPTO_FAIL;
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}
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/* put the generator into a known state: */
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_set(prng->key, 0x00, sizeof(prng->key));
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_set(prng->v, 0x01, sizeof(prng->v));
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tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));
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/* update assumes SOME key has been configured into HMAC */
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update(prng, personalization, plen);
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/* force a reseed before allowing tc_hmac_prng_generate to succeed: */
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prng->countdown = 0;
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return TC_CRYPTO_SUCCESS;
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}
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int tc_hmac_prng_reseed(TCHmacPrng_t prng,
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const uint8_t *seed,
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unsigned int seedlen,
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const uint8_t *additional_input,
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unsigned int additionallen)
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{
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/* input sanity check: */
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if (prng == (TCHmacPrng_t) 0 ||
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seed == (const uint8_t *) 0 ||
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seedlen < MIN_SLEN ||
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seedlen > MAX_SLEN) {
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return TC_CRYPTO_FAIL;
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}
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if (additional_input != (const uint8_t *) 0) {
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/*
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* Abort if additional_input is provided but has inappropriate
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* length
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*/
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if (additionallen == 0 ||
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additionallen > MAX_ALEN) {
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return TC_CRYPTO_FAIL;
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} else {
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/* call update for the seed and additional_input */
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update(prng, seed, seedlen);
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update(prng, additional_input, additionallen);
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}
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} else {
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/* call update only for the seed */
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update(prng, seed, seedlen);
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}
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/* ... and enable hmac_prng_generate */
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prng->countdown = MAX_GENS;
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return TC_CRYPTO_SUCCESS;
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}
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int tc_hmac_prng_generate(uint8_t *out, unsigned int outlen, TCHmacPrng_t prng)
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{
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unsigned int bufferlen;
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/* input sanity check: */
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if (out == (uint8_t *) 0 ||
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prng == (TCHmacPrng_t) 0 ||
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outlen == 0 ||
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outlen > MAX_OUT) {
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return TC_CRYPTO_FAIL;
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} else if (prng->countdown == 0) {
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return TC_HMAC_PRNG_RESEED_REQ;
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}
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prng->countdown--;
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while (outlen != 0) {
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/* operate HMAC in OFB mode to create "random" outputs */
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(void)tc_hmac_init(&prng->h);
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(void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
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(void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
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bufferlen = (TC_SHA256_DIGEST_SIZE > outlen) ?
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outlen : TC_SHA256_DIGEST_SIZE;
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(void)_copy(out, bufferlen, prng->v, bufferlen);
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out += bufferlen;
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outlen = (outlen > TC_SHA256_DIGEST_SIZE) ?
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(outlen - TC_SHA256_DIGEST_SIZE) : 0;
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}
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/* block future PRNG compromises from revealing past state */
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update(prng, prng->v, TC_SHA256_DIGEST_SIZE);
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return TC_CRYPTO_SUCCESS;
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}
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