=pod

=head1 NAME

RAND_add, RAND_poll, RAND_seed, RAND_status, RAND_event, RAND_screen,
RAND_keep_random_devices_open
- add randomness to the PRNG or get its status

=head1 SYNOPSIS

 #include <openssl/rand.h>

 int RAND_status(void);
 int RAND_poll();

 void RAND_add(const void *buf, int num, double randomness);
 void RAND_seed(const void *buf, int num);

 void RAND_keep_random_devices_open(int keep);

The following functions have been deprecated since OpenSSL 1.1.0, and can be
hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
see L<openssl_user_macros(7)>:

 int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
 void RAND_screen(void);

=head1 DESCRIPTION

These functions can be used to seed the random generator and to check its
seeded state.
In general, manual (re-)seeding of the default OpenSSL random generator
(L<RAND_OpenSSL(3)>) is not necessary (but allowed), since it does (re-)seed
itself automatically using trusted system entropy sources.
This holds unless the default RAND_METHOD has been replaced or OpenSSL was
built with automatic reseeding disabled, see L<RAND(7)> for more details.

RAND_status() indicates whether or not the random generator has been sufficiently
seeded. If not, functions such as L<RAND_bytes(3)> will fail.

RAND_poll() uses the system's capabilities to seed the random generator using
random input obtained from polling various trusted entropy sources.
The default choice of the entropy source can be modified at build time,
see L<RAND(7)> for more details.

RAND_add() mixes the B<num> bytes at B<buf> into the internal state
of the random generator.
This function will not normally be needed, as mentioned above.
The B<randomness> argument is an estimate of how much randomness is
contained in
B<buf>, in bytes, and should be a number between zero and B<num>.
Details about sources of randomness and how to estimate their randomness
can be found in the literature; for example [NIST SP 800-90B].
The content of B<buf> cannot be recovered from subsequent random generator output.
Applications that intend to save and restore random state in an external file
should consider using L<RAND_load_file(3)> instead.

NOTE: In FIPS mode, random data provided by the application is not considered to
be a trusted entropy source. It is mixed into the internal state of the RNG as
additional data only and this does not count as a full reseed.
For more details, see L<EVP_RAND(7)>.

RAND_seed() is equivalent to RAND_add() with B<randomness> set to B<num>.

RAND_keep_random_devices_open() is used to control file descriptor
usage by the random seed sources. Some seed sources maintain open file
descriptors by default, which allows such sources to operate in a
chroot(2) jail without the associated device nodes being available. When
the B<keep> argument is zero, this call disables the retention of file
descriptors. Conversely, a nonzero argument enables the retention of
file descriptors. This function is usually called during initialization
and it takes effect immediately. This capability only applies to the default
provider.

RAND_event() and RAND_screen() are equivalent to RAND_poll() and exist
for compatibility reasons only. See HISTORY section below.

=head1 RETURN VALUES

RAND_status() returns 1 if the random generator has been seeded
with enough data, 0 otherwise.

RAND_poll() returns 1 if it generated seed data, 0 otherwise.

RAND_event() returns RAND_status().

The other functions do not return values.

=head1 SEE ALSO

L<RAND_bytes(3)>,
L<RAND_egd(3)>,
L<RAND_load_file(3)>,
L<RAND(7)>
L<EVP_RAND(7)>

=head1 HISTORY

RAND_event() and RAND_screen() were deprecated in OpenSSL 1.1.0 and should
not be used.

=head1 COPYRIGHT

Copyright 2000-2021 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>.

=cut
