=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);

Deprecated:

 #if OPENSSL_API_COMPAT < 0x10100000L

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

 void RAND_screen(void);

 #endif

=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.

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 non-zero argument enables the retention of

file descriptors. This function is usually called during initialization

and it takes effect immediately.

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)>

=head1 HISTORY

RAND_event() and RAND_screen() were deprecated in OpenSSL 1.1.0 and should

not be used.

=head1 COPYRIGHT

Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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