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);
DESCRIPTIONRAND_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
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RAND_add(3) OpenSSL RAND_add(3)
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 VALUESRAND_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 ALSOrand(3), RAND_egd(3), RAND_load_file(3), RAND_cleanup(3)HISTORYRAND_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.
entropy to the PRNG"
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