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EVP_RAND-HASH-DRBG(7)               OpenSSL              EVP_RAND-HASH-DRBG(7)


NAME
       EVP_RAND-HASH-DRBG - The HASH DRBG EVP_RAND implementation

DESCRIPTION
       Support for the hash deterministic random bit generator through the
       EVP_RAND API.

   Identity
       "HASH-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>
       "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 the FIPS provider is installed using the
       -no_drbg_truncated_digests option to fipsinstall, 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 HASH-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 HASH DRBG can be obtained by calling:

        EVP_RAND *rand = EVP_RAND_fetch(NULL, "HASH-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[2], *p = params;
        unsigned int strength = 128;

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

        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_DIGEST, SN_sha512, 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>.

3.5.1                             2025-07-01             EVP_RAND-HASH-DRBG(7)