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.
RAND_egd() retrieves entropy from
the daemon using the daemon's "non-blocking read" command which
shall be answered immediately by the daemon without waiting for additional
entropy to be collected. The write and read socket operations in the
communication are blocking.
Alternatively, the EGD-interface compatible daemon PRNGD can be used. It is
available from
http://prngd.sourceforge.net/ . 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.