RAND_add
Section: OpenSSL (3)
Updated: 2017-05-25
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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.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUES
-
- SEE ALSO
-
- HISTORY
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