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=head1 NAME

OPENSSL_CTX_get0_primary_drbg,
OPENSSL_CTX_get0_public_drbg,
OPENSSL_CTX_get0_private_drbg,
RAND_DRBG_get0_master,
RAND_DRBG_get0_public,
RAND_DRBG_get0_private
- get access to the global RAND_DRBG instances

=head1 SYNOPSIS

 #include <openssl/rand_drbg.h>

 RAND_DRBG *OPENSSL_CTX_get0_primary_drbg(OPENSSL_CTX *ctx);
 RAND_DRBG *OPENSSL_CTX_get0_public_drbg(OPENSSL_CTX *ctx);
 RAND_DRBG *OPENSSL_CTX_get0_private_drbg(OPENSSL_CTX *ctx);
 RAND_DRBG *RAND_DRBG_get0_master(void);
 RAND_DRBG *RAND_DRBG_get0_public(void);
 RAND_DRBG *RAND_DRBG_get0_private(void);


=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<master> DRBG is a global instance, which is not intended to be used
directly, but is used internally to reseed the other two instances.

These functions here provide access to the shared DRBG instances.

=head1 RETURN VALUES

OPENSSL_CTX_get0_primary_drbg() returns a pointer to the I<master> DRBG instance
for the given OPENSSL_CTX B<ctx>.

OPENSSL_CTX_get0_public_drbg() returns a pointer to the I<public> DRBG instance
for the given OPENSSL_CTX B<ctx>.

OPENSSL_CTX_get0_private_drbg() returns a pointer to the I<private> DRBG instance
for the given OPENSSL_CTX B<ctx>.

In all the above cases the B<ctx> parameter can
be NULL in which case the default OPENSSL_CTX is used. RAND_DRBG_get0_master(),
RAND_DRBG_get0_public() and RAND_DRBG_get0_private() are the same as
OPENSSL_CTX_get0_primary_drbg(), OPENSSL_CTX_get0_public_drbg() and
OPENSSL_CTX_get0_private_drbg() respectively except that the default OPENSSL_CTX
is always used.

=head1 NOTES

It is not thread-safe to access the I<master> 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.

=head1 SEE ALSO

L<RAND_DRBG_set_callbacks(3)>,
L<RAND_DRBG_set_reseed_defaults(3)>,
L<RAND_DRBG_set_reseed_interval(3)>,
L<RAND_DRBG_set_reseed_time_interval(3)>,
L<RAND_DRBG_set_callbacks(3)>,
L<RAND_DRBG_generate(3)>,
L<RAND_DRBG(7)>

=head1 HISTORY

The OPENSSL_CTX_get0_primary_drbg(), OPENSSL_CTX_get0_public_drbg() and
OPENSSL_CTX_get0_private_drbg() functions were added in OpenSSL 3.0.

All other RAND_DRBG functions were added in OpenSSL 1.1.1.

=head1 COPYRIGHT

Copyright 2017-2019 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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