RAND_add(3)

     RAND_add(3)            0.9.6h (2000-03-22)            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

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     RAND_add(3)            0.9.6h (2000-03-22)            RAND_add(3)

          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.

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