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.