/usr/man/cat.3/RAND_event.3

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

1.0.2t               Last change: 2019-09-10                    1

RAND_add(3)                  OpenSSL                  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.

1.0.2t               Last change: 2019-09-10                    2

See also RAND_add(3)
See also RAND_screen(3)
See also RAND_seed(3)
See also RAND_status(3)