RAND_set_rand_method(3) OpenSSL RAND_set_rand_method(3)
NAME
RAND_set_rand_method, RAND_get_rand_method, RAND_SSLeay - 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_SSLeay(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_SSLeay().
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 dependant 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 the implementation of RAND_seed(), RAND_bytes(), 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_SSLeay() return pointers to
the respective methods.
NOTES
As of version 0.9.7, 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)
HISTORY
RAND_set_rand_method(), RAND_get_rand_method() and RAND_SSLeay() are available in all versions of
OpenSSL.
In the engine version of version 0.9.6, RAND_set_rand_method() was altered to take an ENGINE pointer
as its argument. As of version 0.9.7, that has been reverted as the ENGINE API transparently
overrides RAND defaults if used, otherwise RAND API functions work as before. RAND_set_rand_engine()
was also introduced in version 0.9.7.
0.9.7l 2002-08-05 RAND_set_rand_method(3)
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