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.\" ========================================================================
.\"
.IX Title "EVP_RAND-SEED-SRC 7ossl"
.TH EVP_RAND-SEED-SRC 7ossl "2024-01-30" "3.2.1" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
EVP_RAND\-SEED\-SRC \- The randomness seed source EVP_RAND implementation
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Support for deterministic random number generator seeding through the
\&\fB\s-1EVP_RAND\s0\fR \s-1API.\s0
.PP
The seed sources used are specified at the time OpenSSL is configured for
building using the \fB\-\-with\-rand\-seed=\fR option.  By default, operating system
randomness sources are used.
.SS "Identity"
.IX Subsection "Identity"
\&\*(L"SEED-SRC\*(R" is the name for this implementation; it can be used with the
\&\fIEVP_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>"
.PD
These parameters work as described in \*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fIEVP_RAND\s0\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, "SEED\-SRC", 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 *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, "SEED\-SRC", 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"
\&\s-1\fIEVP_RAND\s0\fR\|(3),
\&\*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fIEVP_RAND\s0\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2020\-2021 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>.