trusty (3) RAND_SSLeay.3ssl.gz

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.