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.\" ========================================================================
.\"
.IX Title "EVP_RAND-HASH-DRBG 7ossl"
.TH EVP_RAND-HASH-DRBG 7ossl "2026-01-16" "3.5.1" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
EVP_RAND\-HASH\-DRBG \- The HASH DRBG EVP_RAND implementation
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Support for the hash deterministic random bit generator through the
\&\fB\s-1EVP_RAND\s0\fR \s-1API.\s0
.SS "Identity"
.IX Subsection "Identity"
\&\*(L"HASH-DRBG\*(R" is the name for this implementation; it can be used with the
\&\fBEVP_RAND_fetch()\fR function.
.SS "Supported parameters"
.IX Subsection "Supported parameters"
The supported parameters are:
.ie n .IP """state"" (\fB\s-1OSSL_RAND_PARAM_STATE\s0\fR) <integer>" 4
.el .IP "``state'' (\fB\s-1OSSL_RAND_PARAM_STATE\s0\fR) <integer>" 4
.IX Item "state (OSSL_RAND_PARAM_STATE) <integer>"
.PD 0
.ie n .IP """strength"" (\fB\s-1OSSL_RAND_PARAM_STRENGTH\s0\fR) <unsigned integer>" 4
.el .IP "``strength'' (\fB\s-1OSSL_RAND_PARAM_STRENGTH\s0\fR) <unsigned integer>" 4
.IX Item "strength (OSSL_RAND_PARAM_STRENGTH) <unsigned integer>"
.ie n .IP """max_request"" (\fB\s-1OSSL_RAND_PARAM_MAX_REQUEST\s0\fR) <unsigned integer>" 4
.el .IP "``max_request'' (\fB\s-1OSSL_RAND_PARAM_MAX_REQUEST\s0\fR) <unsigned integer>" 4
.IX Item "max_request (OSSL_RAND_PARAM_MAX_REQUEST) <unsigned integer>"
.ie n .IP """reseed_requests"" (\fB\s-1OSSL_DRBG_PARAM_RESEED_REQUESTS\s0\fR) <unsigned integer>" 4
.el .IP "``reseed_requests'' (\fB\s-1OSSL_DRBG_PARAM_RESEED_REQUESTS\s0\fR) <unsigned integer>" 4
.IX Item "reseed_requests (OSSL_DRBG_PARAM_RESEED_REQUESTS) <unsigned integer>"
.ie n .IP """reseed_time_interval"" (\fB\s-1OSSL_DRBG_PARAM_RESEED_TIME_INTERVAL\s0\fR) <integer>" 4
.el .IP "``reseed_time_interval'' (\fB\s-1OSSL_DRBG_PARAM_RESEED_TIME_INTERVAL\s0\fR) <integer>" 4
.IX Item "reseed_time_interval (OSSL_DRBG_PARAM_RESEED_TIME_INTERVAL) <integer>"
.ie n .IP """min_entropylen"" (\fB\s-1OSSL_DRBG_PARAM_MIN_ENTROPYLEN\s0\fR) <unsigned integer>" 4
.el .IP "``min_entropylen'' (\fB\s-1OSSL_DRBG_PARAM_MIN_ENTROPYLEN\s0\fR) <unsigned integer>" 4
.IX Item "min_entropylen (OSSL_DRBG_PARAM_MIN_ENTROPYLEN) <unsigned integer>"
.ie n .IP """max_entropylen"" (\fB\s-1OSSL_DRBG_PARAM_MAX_ENTROPYLEN\s0\fR) <unsigned integer>" 4
.el .IP "``max_entropylen'' (\fB\s-1OSSL_DRBG_PARAM_MAX_ENTROPYLEN\s0\fR) <unsigned integer>" 4
.IX Item "max_entropylen (OSSL_DRBG_PARAM_MAX_ENTROPYLEN) <unsigned integer>"
.ie n .IP """min_noncelen"" (\fB\s-1OSSL_DRBG_PARAM_MIN_NONCELEN\s0\fR) <unsigned integer>" 4
.el .IP "``min_noncelen'' (\fB\s-1OSSL_DRBG_PARAM_MIN_NONCELEN\s0\fR) <unsigned integer>" 4
.IX Item "min_noncelen (OSSL_DRBG_PARAM_MIN_NONCELEN) <unsigned integer>"
.ie n .IP """max_noncelen"" (\fB\s-1OSSL_DRBG_PARAM_MAX_NONCELEN\s0\fR) <unsigned integer>" 4
.el .IP "``max_noncelen'' (\fB\s-1OSSL_DRBG_PARAM_MAX_NONCELEN\s0\fR) <unsigned integer>" 4
.IX Item "max_noncelen (OSSL_DRBG_PARAM_MAX_NONCELEN) <unsigned integer>"
.ie n .IP """max_perslen"" (\fB\s-1OSSL_DRBG_PARAM_MAX_PERSLEN\s0\fR) <unsigned integer>" 4
.el .IP "``max_perslen'' (\fB\s-1OSSL_DRBG_PARAM_MAX_PERSLEN\s0\fR) <unsigned integer>" 4
.IX Item "max_perslen (OSSL_DRBG_PARAM_MAX_PERSLEN) <unsigned integer>"
.ie n .IP """max_adinlen"" (\fB\s-1OSSL_DRBG_PARAM_MAX_ADINLEN\s0\fR) <unsigned integer>" 4
.el .IP "``max_adinlen'' (\fB\s-1OSSL_DRBG_PARAM_MAX_ADINLEN\s0\fR) <unsigned integer>" 4
.IX Item "max_adinlen (OSSL_DRBG_PARAM_MAX_ADINLEN) <unsigned integer>"
.ie n .IP """reseed_counter"" (\fB\s-1OSSL_DRBG_PARAM_RESEED_COUNTER\s0\fR) <unsigned integer>" 4
.el .IP "``reseed_counter'' (\fB\s-1OSSL_DRBG_PARAM_RESEED_COUNTER\s0\fR) <unsigned integer>" 4
.IX Item "reseed_counter (OSSL_DRBG_PARAM_RESEED_COUNTER) <unsigned integer>"
.ie n .IP """properties"" (\fB\s-1OSSL_DRBG_PARAM_PROPERTIES\s0\fR) <\s-1UTF8\s0 string>" 4
.el .IP "``properties'' (\fB\s-1OSSL_DRBG_PARAM_PROPERTIES\s0\fR) <\s-1UTF8\s0 string>" 4
.IX Item "properties (OSSL_DRBG_PARAM_PROPERTIES) <UTF8 string>"
.ie n .IP """digest"" (\fB\s-1OSSL_DRBG_PARAM_DIGEST\s0\fR) <\s-1UTF8\s0 string>" 4
.el .IP "``digest'' (\fB\s-1OSSL_DRBG_PARAM_DIGEST\s0\fR) <\s-1UTF8\s0 string>" 4
.IX Item "digest (OSSL_DRBG_PARAM_DIGEST) <UTF8 string>"
.PD
These parameters work as described in \*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fBEVP_RAND\s0\fR\|(3).
.ie n .IP """fips-indicator"" (\fB\s-1OSSL_DRBG_PARAM_FIPS_APPROVED_INDICATOR\s0\fR) <integer>" 4
.el .IP "``fips-indicator'' (\fB\s-1OSSL_DRBG_PARAM_FIPS_APPROVED_INDICATOR\s0\fR) <integer>" 4
.IX Item "fips-indicator (OSSL_DRBG_PARAM_FIPS_APPROVED_INDICATOR) <integer>"
.PD 0
.ie n .IP """digest-check"" (\fB\s-1OSSL_DRBG_PARAM_FIPS_DIGEST_CHECK\s0\fR) <integer>" 4
.el .IP "``digest-check'' (\fB\s-1OSSL_DRBG_PARAM_FIPS_DIGEST_CHECK\s0\fR) <integer>" 4
.IX Item "digest-check (OSSL_DRBG_PARAM_FIPS_DIGEST_CHECK) <integer>"
.PD
These parameters work as described in \*(L"\s-1PARAMETERS\*(R"\s0 in \fBprovider\-rand\fR\|(7).
.SH "NOTES"
.IX Header "NOTES"
When the \s-1FIPS\s0 provider is installed using the \fB\-no_drbg_truncated_digests\fR
option to fipsinstall, only these digests are permitted (as per
\&\s-1FIPS 140\-3 IG D.R\s0 <https://csrc.nist.gov/CSRC/media/Projects/cryptographic-module-validation-program/documents/fips%20140-3/FIPS%20140-3%20IG.pdf>):
.PP
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.
.IP "\s-1SHA\-1\s0" 4
.IX Item "SHA-1"
.PD 0
.IP "\s-1SHA2\-256\s0" 4
.IX Item "SHA2-256"
.IP "\s-1SHA2\-512\s0" 4
.IX Item "SHA2-512"
.IP "\s-1SHA3\-256\s0" 4
.IX Item "SHA3-256"
.IP "\s-1SHA3\-512\s0" 4
.IX Item "SHA3-512"
.PD
.PP
A context for \s-1HASH DRBG\s0 can be obtained by calling:
.PP
.Vb 2
\& EVP_RAND *rand = EVP_RAND_fetch(NULL, "HASH\-DRBG", NULL);
\& EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand, NULL);
.Ve
.SH "EXAMPLES"
.IX Header "EXAMPLES"
.Vb 5
\& 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);
.Ve
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
\&\s-1NIST SP 800\-90A\s0 and \s-1SP 800\-90B\s0
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\s-1\fBEVP_RAND\s0\fR\|(3),
\&\*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fBEVP_RAND\s0\fR\|(3),
\&\fBopenssl\-fipsinstall\fR\|(1)
.SH "HISTORY"
.IX Header "HISTORY"
OpenSSL 3.1.1 introduced the \fB\-no_drbg_truncated_digests\fR option to
fipsinstall which restricts the permitted digests when using the \s-1FIPS\s0
provider in a complaint manner.  For details refer to
\&\s-1FIPS 140\-3 IG D.R\s0 <https://csrc.nist.gov/CSRC/media/Projects/cryptographic-module-validation-program/documents/fips%20140-3/FIPS%20140-3%20IG.pdf>.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2020\-2025 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.
