RAND_set_rand_method.3ssl man page

RAND_set_rand_method, RAND_get_rand_method, RAND_OpenSSL — select RAND method


#include <openssl/rand.h>
void RAND_set_rand_method(const RAND_METHOD *meth);
const RAND_METHOD *RAND_get_rand_method(void);


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);

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.


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)


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