EVP_RAND-HMAC-DRBG(7SSL)

📦
version 4.0.3 · 13 versions
, in ubuntu stonking

✨ NAME ✨

EVP_RAND-HMAC-DRBG — the HMAC DRBG EVP_RAND implementation 💅

(yes bestie, this is the EVP_RAND-HMAC-DRBG(7SSL) page, she got her own whole manual, main character energy fr)

💖 DESCRIPTION 💖

So okay, this is support for the HMAC deterministic random bit generator, all cozy inside the EVP_RAND API. That's the whole vibe. 🌸

🪪 Identity

"HMAC-DRBG" is literally the name for this implementation, no cap — and you can pass it straight into the EVP_RAND_fetch() function. That's it, that's the identity. ✨

🎀 Supported parameters

Here's everything she'll accept, bestie:

  • "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 ones work exactly 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>

And these two cuties work as described in "PARAMETERS" in provider-rand(7). 💜

🔥 NOTES 🔥

Okay important part, listen up. 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>):

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 🌈

Here's the whole thing in action, bestie, copy-paste ready:

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

*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 — she follows the specs, obviously. 💅

🦋 SEE ALSO 🦋

⭐ 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 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>.

okay that's the whole page bestie, you ate that 🫶 — this was 4.0.3, dated 2026-09-29, and that's the EVP_RAND-HMAC-DRBG(7SSL) tea. mwah 💖✨

📦 where this page comes from