EVP_RAND-HMAC-DRBG(7ossl)

📦
version 15.1 · 3 versions
, in freebsd 15.1

💖 EVP_RAND-HMAC-DRBG 💖

okay so bestie, welcome to the 7ossl manual page for the HMAC DRBG EVP_RAND implementation — yes that's a mouthful, but we're gonna slay it together 🫶

✨ NAME ✨

EVP_RAND-HMAC-DRBG — literally the HMAC DRBG EVP_RAND implementation, no cap 🌸

🦋 DESCRIPTION 🦋

So this is the support for the HMAC deterministic random bit generator, accessed through the EVP_RAND API. Iconic behaviour, honestly 👑

🎀 Identity 🎀

"HMAC-DRBG" is the name for this implementation — that's its whole name, that's its whole vibe. You can use it with the EVP_RAND_fetch() function. periodt 💅

🌈 Supported parameters 🌈

Here's the full lineup of supported parameters, and yes I'm giving you all of them because we don't do partial info in this house:

  • "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>

Those ones all work exactly as described in "PARAMETERS" in EVP_RAND(3). iykyk 📖

and then these two cuties:

  • "fips-indicator" (OSSL_DRBG_PARAM_FIPS_APPROVED_INDICATOR) <integer>
  • "digest-check" (OSSL_DRBG_PARAM_FIPS_DIGEST_CHECK) <integer>

which work as described in "PARAMETERS" in provider-rand(7) ✨

💀 NOTES 💀

okay so heads up, this part is important — when you're 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](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

That's the whole approved list, bestie. no substitutions, no vibes-based crypto 🙈

and 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);

like, that's the whole bootstrap. go off 💜

⭐ EXAMPLES ⭐

here's the full little demo, copied exactly because accuracy is the moment:

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);

fetch, wrap, free the rand, set the params, instantiate, generate, free the ctx — clean, tidy, done 🎀

👑 CONFORMING TO 👑

NIST SP 800-90A and SP 800-90B — standards-approved behaviour, we love a certified icon 💅

🔥 SEE ALSO 🔥

go read these next, bestie:

🌸 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. (yes, "complaint" — that's what it says, we're keeping it fr fr 😭) 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](https://csrc.nist.gov/CSRC/media/Projects/cryptographic-module-validation-program/documents/fips%20140-3/FIPS%20140-3%20IG.pdf).

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](https://www.openssl.org/source/license.html).

aaaand that's the page! this was OpenSSL 3.5.6, dated 2026-04-07, brought to you by the EVP_RAND-HMAC-DRBG(7ossl) girlies 💖 stay random, stay deterministic, stay slay ✨🦋

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