NAME

       EVP_RAND-HMAC-DRBG - The HMAC DRBG EVP_RAND implementation

DESCRIPTION

       Support for the HMAC deterministic random bit generator through the EVP_RAND API.

   Identity
       "HMAC-DRBG" is the name for this implementation; it can be used with the EVP_RAND_fetch() function.

   Supported parameters
       The supported parameters are:

       "state" (OSSL_RAND_PARAM_STATE) <integer>
       "strength" (OSSL_RAND_PARAM_STRENGTH) <unsigned integer>
       "max_request" (OSSL_RAND_PARAM_MAX_REQUEST) <unsigned integer>
       "reseed_requests" (OSSL_DRBG_PARAM_RESEED_REQUESTS) <unsigned integer>
       "reseed_time_interval" (OSSL_DRBG_PARAM_RESEED_TIME_INTERVAL) <integer>
       "min_entropylen" (OSSL_DRBG_PARAM_MIN_ENTROPYLEN) <unsigned integer>
       "max_entropylen" (OSSL_DRBG_PARAM_MAX_ENTROPYLEN) <unsigned integer>
       "min_noncelen" (OSSL_DRBG_PARAM_MIN_NONCELEN) <unsigned integer>
       "max_noncelen" (OSSL_DRBG_PARAM_MAX_NONCELEN) <unsigned integer>
       "max_perslen" (OSSL_DRBG_PARAM_MAX_PERSLEN) <unsigned integer>
       "max_adinlen" (OSSL_DRBG_PARAM_MAX_ADINLEN) <unsigned integer>
       "reseed_counter" (OSSL_DRBG_PARAM_RESEED_COUNTER) <unsigned integer>
       "properties" (OSSL_DRBG_PARAM_PROPERTIES) <UTF8 string>
       "mac" (OSSL_DRBG_PARAM_MAC) <UTF8 string>
       "digest" (OSSL_DRBG_PARAM_DIGEST) <UTF8 string>
           These parameters work as described in "PARAMETERS" in EVP_RAND(3).

       "fips-indicator" (OSSL_DRBG_PARAM_FIPS_APPROVED_INDICATOR) <integer>
       "digest-check" (OSSL_DRBG_PARAM_FIPS_DIGEST_CHECK) <integer>
           These parameters work as described in "PARAMETERS" in provider-rand(7).

NOTES

       When   using   the  FIPS  provider,  only  these  digests  are  permitted  (as  per  FIPS  140-3  IG  D.R
       <https://csrc.nist.gov/CSRC/media/Projects/cryptographic-module-validation-
       program/documents/fips%20140-3/FIPS%20140-3%20IG.pdf>):

       The default HMAC-DRBG implementation attempts to fetch the required internal algorithms from the provider
       they are built into (eg the default provider) regardless of the properties provided. Should the  provider
       not implement the required algorithms then properties will be used to find a different implementation.

       SHA-1
       SHA2-256
       SHA2-512
       SHA3-256
       SHA3-512

       A context for HMAC DRBG can be obtained by calling:

        EVP_RAND *rand = EVP_RAND_fetch(NULL, "HMAC-DRBG", NULL);
        EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand, NULL);

EXAMPLES

        EVP_RAND *rand;
        EVP_RAND_CTX *rctx;
        unsigned char bytes[100];
        OSSL_PARAM params[3], *p = params;
        unsigned int strength = 128;

        rand = EVP_RAND_fetch(NULL, "HMAC-DRBG", NULL);
        rctx = EVP_RAND_CTX_new(rand, NULL);
        EVP_RAND_free(rand);

        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_MAC, SN_hmac, 0);
        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_DIGEST, SN_sha256, 0);
        *p = OSSL_PARAM_construct_end();
        EVP_RAND_instantiate(rctx, strength, 0, NULL, 0, params);

        EVP_RAND_generate(rctx, bytes, sizeof(bytes), strength, 0, NULL, 0);

        EVP_RAND_CTX_free(rctx);

CONFORMING TO

       NIST SP 800-90A and SP 800-90B

SEE ALSO

       EVP_RAND(3), "PARAMETERS" in EVP_RAND(3), openssl-fipsinstall(1)

HISTORY

       OpenSSL  3.1.1  introduced  the  -no_drbg_truncated_digests  option  to  fipsinstall  which restricts the
       permitted digests when using the FIPS provider in a complaint manner.  For details refer to FIPS 140-3 IG
       D.R                           <https://csrc.nist.gov/CSRC/media/Projects/cryptographic-module-validation-
       program/documents/fips%20140-3/FIPS%20140-3%20IG.pdf>).

COPYRIGHT

       Copyright 2020-2025 The OpenSSL Project Authors. All Rights Reserved.

       Licensed  under  the  Apache License 2.0 (the "License").  You may not use this file except in compliance
       with the License.  You can obtain  a  copy  in  the  file  LICENSE  in  the  source  distribution  or  at
       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04                           EVP_RAND-HMAC-DRBG(7SSL)