| /* hmac_prng.c - TinyCrypt implementation of HMAC-PRNG */ |
| |
| /* |
| * Copyright (C) 2017 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 unsigned int 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 unsigned int 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 unsigned int 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 unsigned int 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 32-bit unsigned int variable, while SP800-90A specifies a maximum of 2^48. |
| */ |
| static const unsigned int MAX_GENS = UINT32_MAX; |
| |
| /* |
| * maximum bytes per generate call; |
| * SP800-90A specifies a maximum up to 2^19. |
| */ |
| static const unsigned int MAX_OUT = (1 << 19); |
| |
| /* |
| * Assumes: prng != NULL, e != NULL, len >= 0. |
| */ |
| static void update(TCHmacPrng_t prng, const uint8_t *e, unsigned int 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); |
| } |
| |
| int tc_hmac_prng_init(TCHmacPrng_t prng, |
| const uint8_t *personalization, |
| unsigned int 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; |
| } |
| |
| int tc_hmac_prng_reseed(TCHmacPrng_t prng, |
| const uint8_t *seed, |
| unsigned int seedlen, |
| const uint8_t *additional_input, |
| unsigned int 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; |
| } |
| |
| int tc_hmac_prng_generate(uint8_t *out, unsigned int outlen, TCHmacPrng_t prng) |
| { |
| unsigned int 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; |
| } |