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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. Suitable 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 recovered 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 transparently. 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 arguments 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 convenience of Windows programmers. It adds the
       current contents 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 randomness. 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 versions of SSLeay and OpenSSL. RAND_add() and
       RAND_status() have been added in OpenSSL 0.9.5, RAND_event() in OpenSSL 0.9.5a.



0.9.8                                            2000-03-22                                      RAND_add(3)