=pod

=head1 NAME

RAND_get0_primary,
RAND_get0_public,
RAND_get0_private,
RAND_set0_public,
RAND_set0_private
- get access to the global EVP_RAND_CTX instances

=head1 SYNOPSIS

 #include <openssl/rand.h>

 EVP_RAND_CTX *RAND_get0_primary(OSSL_LIB_CTX *ctx);
 EVP_RAND_CTX *RAND_get0_public(OSSL_LIB_CTX *ctx);
 EVP_RAND_CTX *RAND_get0_private(OSSL_LIB_CTX *ctx);
 int RAND_set0_public(OSSL_LIB_CTX *ctx, EVP_RAND_CTX *rand);
 int RAND_set0_private(OSSL_LIB_CTX *ctx, EVP_RAND_CTX *rand);

=head1 DESCRIPTION

The default RAND API implementation (RAND_OpenSSL()) utilizes three
shared DRBG instances which are accessed via the RAND API:

The I<public> and I<private> DRBG are thread-local instances, which are used
by RAND_bytes() and RAND_priv_bytes(), respectively.
The I<primary> DRBG is a global instance, which is not intended to be used
directly, but is used internally to reseed the other two instances.

The three get functions provide access to the shared DRBG instances.

The two set functions allow the public and private DRBG instances to be
replaced by another random number generator.

=head1 RETURN VALUES

RAND_get0_primary() returns a pointer to the I<primary> DRBG instance
for the given OSSL_LIB_CTX B<ctx>.

RAND_get0_public() returns a pointer to the I<public> DRBG instance
for the given OSSL_LIB_CTX B<ctx>.

RAND_get0_private() returns a pointer to the I<private> DRBG instance
for the given OSSL_LIB_CTX B<ctx>.

RAND_set0_public() and RAND_set0_private() return 1 on success and 0
on error.

=head1 NOTES

It is not thread-safe to access the I<primary> DRBG instance.
The I<public> and I<private> DRBG instance can be accessed safely, because
they are thread-local. Note however, that changes to these two instances
apply only to the current thread.

For that reason it is recommended not to change the settings of these
three instances directly.
Instead, an application should change the default settings for new DRBG instances
at initialization time, before creating additional threads.

During initialization, it is possible to change the reseed interval
and reseed time interval.
It is also possible to exchange the reseeding callbacks entirely.

To set the type of DRBG that will be instantiated, use the
L<RAND_set_DRBG_type(3)> call before accessing the random number generation
infrastructure.

The two set functions, operate on the current thread.  If you want to
use the same random number generator across all threads, each thread
must individually call the set functions.

=head1 SEE ALSO

L<EVP_RAND(3)>,
L<RAND_set_DRBG_type(3)>

=head1 HISTORY

RAND_set0_public() and RAND_set0_private() were added in OpenSSL 3.1.

The remaining functions were added in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2020-2024 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
L<https://www.openssl.org/source/license.html>.

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