RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen - add entropy to the
void RAND_seed(const void *buf, int num);
void RAND_add(const void *buf, int num, double entropy);
int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
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
(the lower bound of) an estimate of how much randomness is contained in
, measured in bytes. Details about sources of randomness and how to
estimate their entropy can be found in the literature, e.g. RFC 1750.
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()
is equivalent to RAND_add()
when num ==
collects the entropy from Windows events such as mouse
movements and other user interaction. It should be called with the
arguments of all
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.
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
is a significantly better source of randomness. It should
be noted that both methods cannot be used on servers that run without user
return 1 if the PRNG has been
seeded with enough data, 0 otherwise.
The other functions do not return values.
are available in all versions of
SSLeay and OpenSSL. RAND_add()
have been added
in OpenSSL 0.9.5, RAND_event()
in OpenSSL 0.9.5a.