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RAND_SET_RAND_METHOD(3) OpenSSL RAND_SET_RAND_METHOD(3)

NAME

RAND_set_rand_method, RAND_get_rand_method, RAND_OpenSSL - select RAND method

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);

DESCRIPTION

A 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 ENGINE API calls.
Initially, the default RAND_METHOD is the OpenSSL internal implementation, as returned by RAND_OpenSSL().
RAND_set_default_method() makes meth the method for PRNG use. 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.

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.

RETURN VALUES

RAND_set_rand_method() returns no value. RAND_get_rand_method() and RAND_OpenSSL() return pointers to the respective methods.

NOTES

RAND_METHOD implementations are grouped together with other algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in 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.

SEE ALSO

rand(3), engine(3)

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 <https://www.openssl.org/source/license.html>.
2017-05-25 1.1.0f