man RAND_egd - Man page for RAND_egd
June 1, 2007 – 1:43 amRAND_egd
Section: OpenSSL (3)
Updated: 2001–02–10
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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.