RAND_add(3)                 OpenSSL                 RAND_add(3)





NAME
       RAND_add, RAND_seed, RAND_status, RAND_event,
       RAND_screen - add entropy to the PRNG

SYNOPSIS
        #include <openssl/rand.h>

        void RAND_seed(const void *buf, int num);

        void RAND_add(const void *buf, int num, double entropy);

        int  RAND_status(void);

        int  RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
        void RAND_screen(void);

DESCRIPTION
       RAND_add() mixes the num bytes at buf into the PRNG
       state. Thus, if the data at buf are unpredictable to an
       adversary, this increases the uncertainty about the
       state and makes the PRNG output less predictable. Suit-
       able input comes from user interaction (random key
       presses, mouse movements) and certain hardware events.
       The entropy argument is (the lower bound of) an estimate
       of how much randomness is contained in buf, measured in
       bytes. Details about sources of randomness and how to
       estimate their entropy can be found in the literature,
       e.g. RFC 1750.

       RAND_add() may be called with sensitive data such as
       user entered passwords. The seed values cannot be recov-
       ered from the PRNG output.

       OpenSSL makes sure that the PRNG state is unique for
       each thread. On systems that provide "/dev/urandom", the
       randomness device is used to seed the PRNG transpar-
       ently. However, on all other systems, the application is
       responsible for seeding the PRNG by calling RAND_add(),
       RAND_egd(3) or RAND_load_file(3).

       RAND_seed() is equivalent to RAND_add() when num ==
       entropy.

       RAND_event() collects the entropy from Windows events
       such as mouse movements and other user interaction. It
       should be called with the iMsg, wParam and lParam argu-
       ments of all messages sent to the window procedure. It
       will estimate the entropy contained in the event message
       (if any), and add it to the PRNG. The program can then
       process the messages as usual.

       The RAND_screen() function is available for the conve-
       nience of Windows programmers. It adds the current con-
       tents of the screen to the PRNG.  For applications that
       can catch Windows events, seeding the PRNG by calling
       RAND_event() is a significantly better source of random-
       ness. It should be noted that both methods cannot be
       used on servers that run without user interaction.

RETURN VALUES
       RAND_status() and RAND_event() return 1 if the PRNG has
       been seeded with enough data, 0 otherwise.

       The other functions do not return values.

SEE ALSO
       rand(3), RAND_egd(3), RAND_load_file(3), RAND_cleanup(3)

HISTORY
       RAND_seed() and RAND_screen() are available in all ver-
       sions of SSLeay and OpenSSL. RAND_add() and RAND_sta-
       tus() have been added in OpenSSL 0.9.5, RAND_event() in
       OpenSSL 0.9.5a.



0.9.7c                     2000-03-22               RAND_add(3)
