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);

 void 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.

Initially, the default B<RAND_METHOD> is the OpenSSL internal implementation,
as returned by RAND_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().

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 {
     void (*seed)(const void *buf, int num);
     int (*bytes)(unsigned char *buf, int num);
     void (*cleanup)(void);
     void (*add)(const void *buf, int num, int randomness);
     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 no value. 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)>

=head1 COPYRIGHT

Copyright 2000-2017 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>.

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