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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
  The RAND_add() function 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.

  The RAND_add() function 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 the RAND_add(), RAND_egd() or
  RAND_load_file() functions.

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

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

  The other functions do not return values.

HISTORY
  The RAND_seed() and RAND_screen() functions are available in all versions
  of SSLeay and OpenSSL. The RAND_add() and RAND_status() functions have been
  added in OpenSSL 0.9.5, and RAND_event() in OpenSSL 0.9.5a.

SEE ALSO
  Functions: rand_ssl(3), RAND_egd(3), RAND_load_file(3), RAND_cleanup(3)

Index for Section 3

Alphabetical listing for R

Top of page