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.\" -*- mode: troff; coding: utf-8 -*-
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.\" ========================================================================
.\"
.IX Title "EVP_RAND-JITTER 7ossl"
.TH EVP_RAND-JITTER 7ossl 2025-07-01 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\-JITTER \- The randomness seed source EVP_RAND implementation
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Support for deterministic random number generator seeding through the
\&\fBEVP_RAND\fR API.
.PP
This software seed source produces randomness based on tiny CPU
"jitter" fluctuations.
.PP
It is available when OpenSSL is compiled with \fBenable-jitter\fR
option. When available it is listed in \fBopenssl list
\&\-random\-generators\fR and \fBopenssl info \-seeds\fR.
.SS Identity
.IX Subsection "Identity"
"JITTER" 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:
.IP """state"" (\fBOSSL_RAND_PARAM_STATE\fR) <integer>" 4
.IX Item """state"" (OSSL_RAND_PARAM_STATE) <integer>"
.PD 0
.IP """strength"" (\fBOSSL_RAND_PARAM_STRENGTH\fR) <unsigned integer>" 4
.IX Item """strength"" (OSSL_RAND_PARAM_STRENGTH) <unsigned integer>"
.IP """max_request"" (\fBOSSL_RAND_PARAM_MAX_REQUEST\fR) <unsigned integer>" 4
.IX Item """max_request"" (OSSL_RAND_PARAM_MAX_REQUEST) <unsigned integer>"
.PD
These parameters work as described in "PARAMETERS" in \fBEVP_RAND\fR\|(3).
.SH NOTES
.IX Header "NOTES"
A context for the seed source can be obtained by calling:
.PP
.Vb 2
\& EVP_RAND *rand = EVP_RAND_fetch(NULL, "JITTER", NULL);
\& EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand, NULL);
.Ve
.PP
The \fBenable-jitter\fR option was added in OpenSSL 3.4.
.PP
By specifying the \fBenable-fips-jitter\fR configuration option, the FIPS
provider will use an internal jitter source for its entropy. Enabling
this option will cause the FIPS provider to operate in a non-compliant
mode unless an entropy assessment
ESV <https://csrc.nist.gov/Projects/cryptographic-module-validation-program/entropy-validations>
and validation through the
CMVP <https://csrc.nist.gov/projects/cryptographic-module-validation-program>
are additionally conducted. This option was added in OpenSSL 3.5.
.SH EXAMPLES
.IX Header "EXAMPLES"
.Vb 5
\& EVP_RAND *rand;
\& EVP_RAND_CTX *seed, *rctx;
\& unsigned char bytes[100];
\& OSSL_PARAM params[2], *p = params;
\& unsigned int strength = 128;
\&
\& /* Create and instantiate a seed source */
\& rand = EVP_RAND_fetch(NULL, "JITTER", NULL);
\& seed = EVP_RAND_CTX_new(rand, NULL);
\& EVP_RAND_instantiate(seed, strength, 0, NULL, 0, NULL);
\& EVP_RAND_free(rand);
\&
\& /* Feed this into a DRBG */
\& rand = EVP_RAND_fetch(NULL, "CTR\-DRBG", NULL);
\& rctx = EVP_RAND_CTX_new(rand, seed);
\& EVP_RAND_free(rand);
\&
\& /* Configure the DRBG */
\& *p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_CIPHER,
\& SN_aes_256_ctr, 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);
\& EVP_RAND_CTX_free(seed);
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_RAND\fR\|(3),
"PARAMETERS" in \fBEVP_RAND\fR\|(3)
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright 2024 The OpenSSL Project Authors. All Rights Reserved.
.PP
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>.

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