NAME
RAND_egd — query entropy gathering daemon
Synopsis
#include <openssl/rand.h>
int
RAND_egd(const char *path);
int RAND_egd_bytes(const char
*path, int bytes);
int RAND_query_egd_bytes(const char
*path, unsigned char *buf, int bytes);
DESCRIPTION
RAND_egd() queries the entropy gathering daemon EGD on socket path.
It queries 255 bytes and uses RAND_add(3) to seed the OpenSSL built-in
PRNG. RAND_egd(path) is a wrapper for RAND_egd_bytes(path, 255);
RAND_egd_bytes() queries the entropy gathering daemon EGD
on socket path. It queries bytes bytes
and uses RAND_add(3) to seed the OpenSSL built-in
PRNG. This function is more flexible than RAND_egd(). When only
one secret key must be generated, it is not necessary to request
the full amount 255 bytes from the EGD socket. This can be advantageous,
since the amount of entropy that can be retrieved from EGD over
time is limited.
RAND_query_egd_bytes() performs the actual query of the EGD
daemon on socket path. If buf is
given, bytes bytes are queried and written
into buf. If buf is NULL, bytes bytes
are queried and used to seed the OpenSSL built-in PRNG using RAND_add(3).
NOTES
On systems without /dev/*random devices providing entropy
from the kernel, the EGD entropy gathering daemon can be used to
collect entropy. It provides a socket interface through which entropy
can be gathered in chunks up to 255 bytes. Several chunks can be
queried during one connection.
EGD is available from http://www.lothar.com/tech/crypto/ (perl
Makefile.PL; make; make install to install). It is run
as egd path, where path is an absolute path designating a socket. When RAND_egd()
is called with that path as an argument, it tries to read random
bytes that EGD has collected. The read is performed in non-blocking
mode.
Alternatively, the EGD-interface compatible daemon PRNGD can
be used. It is available from http://www.aet.tu-cottbus.de/personen/jaenicke/postfix_tls/prngd.html
. PRNGD does employ an internal PRNG itself and can therefore never
run out of entropy.
OpenSSL automatically queries EGD when entropy is requested
via RAND_bytes() or the status is checked via RAND_status() for
the first time, if the socket is located at /var/run/egd-pool, /dev/egd-pool
or /etc/egd-pool.
RETURN VALUE
RAND_egd() and RAND_egd_bytes() return the number of bytes
read from the daemon on success, and -1 if the connection failed
or the daemon did not return enough data to fully seed the PRNG.
RAND_query_egd_bytes() returns the number of bytes read from
the daemon on success, and -1 if the connection failed. The PRNG
state is not considered.
SEE ALSO
rand(3), RAND_add(3), RAND_cleanup(3)
HISTORY
RAND_egd() is available since OpenSSL 0.9.5.
RAND_egd_bytes() is available since OpenSSL 0.9.6.
RAND_query_egd_bytes() is available since OpenSSL 0.9.7.
The automatic query of /var/run/egd-pool et al was added in
OpenSSL 0.9.7.
