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 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 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.