openssl/doc/man3/RAND_set_rand_method.pod

=pod

=head1 NAME

RAND_set_rand_method, RAND_get_rand_method, RAND_OpenSSL - select RAND method

=head1 SYNOPSIS

 #include <openssl/rand.h>

 RAND_METHOD *RAND_OpenSSL(void);

 int RAND_set_rand_method(const RAND_METHOD *meth);

 const RAND_METHOD *RAND_get_rand_method(void);

=head1 DESCRIPTION

A B<RAND_METHOD> specifies the functions that OpenSSL uses for random number
generation.

RAND_OpenSSL() returns the default B<RAND_METHOD> implementation by OpenSSL.
This implementation ensures that the PRNG state is unique for each thread.

If an B<ENGINE> is loaded that provides the RAND API, however, it will
be used instead of the method returned by RAND_OpenSSL().  This is deprecated
in OpenSSL 3.0.

RAND_set_rand_method() makes B<meth> the method for PRNG use.  If an
ENGINE was providing the method, it will be released first.

RAND_get_rand_method() returns a pointer to the current B<RAND_METHOD>.

=head1 THE RAND_METHOD STRUCTURE

 typedef struct rand_meth_st {
     int (*seed)(const void *buf, int num);
     int (*bytes)(unsigned char *buf, int num);
     void (*cleanup)(void);
     int (*add)(const void *buf, int num, double entropy);
     int (*pseudorand)(unsigned char *buf, int num);
     int (*status)(void);
 } RAND_METHOD;

The fields point to functions that are used by, in order,
RAND_seed(), RAND_bytes(), internal RAND cleanup, RAND_add(), RAND_pseudo_rand()
and RAND_status().
Each pointer may be NULL if the function is not implemented.

=head1 RETURN VALUES

RAND_set_rand_method() returns 1 on success and 0 on failure.
RAND_get_rand_method() and RAND_OpenSSL() return pointers to the respective
methods.

=head1 SEE ALSO

L<RAND_bytes(3)>,
L<ENGINE_by_id(3)>,
L<RAND(7)>

=head1 HISTORY

The ability for an B<ENGINE> to replace the RAND API was deprecated in
OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2000-2020 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