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=head1 NAME

RAND_set_rand_method, RAND_get_rand_method, RAND_OpenSSL - select RAND method

=head1 SYNOPSIS

 #include <openssl/rand.h>

 void RAND_set_rand_method(const RAND_METHOD *meth);

 const RAND_METHOD *RAND_get_rand_method(void);

 RAND_METHOD *RAND_OpenSSL(void);

=head1 DESCRIPTION

A B<RAND_METHOD> specifies the functions that OpenSSL uses for random number
generation. By modifying the method, alternative implementations such as
hardware RNGs may be used. IMPORTANT: See the NOTES section for important
information about how these RAND API functions are affected by the use of
B<ENGINE> API calls.

Initially, the default RAND_METHOD is the OpenSSL internal implementation, as
returned by RAND_OpenSSL().

RAND_set_default_method() makes B<meth> the method for PRNG use. B<NB>: This is
true only whilst no ENGINE has been set as a default for RAND, so this function
is no longer recommended.

RAND_get_default_method() returns a pointer to the current RAND_METHOD.
However, the meaningfulness of this result is dependent on whether the ENGINE
API is being used, so this function is no longer recommended.

=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 entropy);
        int (*pseudorand)(unsigned char *buf, int num);
        int (*status)(void);
 } RAND_METHOD;

The components point to method implementations used by (or called by), in order,
RAND_seed(), RAND_bytes(), internal RAND cleanup, RAND_add(), RAND_pseudo_rand()
and RAND_status().
Each component 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 NOTES

RAND_METHOD implementations are grouped together with other
algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in B<ENGINE> modules. If a
default ENGINE is specified for RAND functionality using an ENGINE API function,
that will override any RAND defaults set using the RAND API (ie.
RAND_set_rand_method()). For this reason, the ENGINE API is the recommended way
to control default implementations for use in RAND and other cryptographic
algorithms.

=head1 SEE ALSO

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

=head1 COPYRIGHT

Copyright 2000-2016 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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