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.\" ======================================================================
.\"
.IX Title "RAND_egd 3"
.TH RAND_egd 3 "0.9.6e" "2001-02-17" "OpenSSL"
.UC
.SH "NAME"
RAND_egd \- query entropy gathering daemon
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rand.h>
.Ve
.Vb 2
\& int RAND_egd(const char *path);
\& int RAND_egd_bytes(const char *path, int bytes);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIRAND_egd()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
It queries 255 bytes and uses RAND_add(3) to seed the
OpenSSL built-in \s-1PRNG\s0. RAND_egd(path) is a wrapper for
RAND_egd_bytes(path, 255);
.PP
\&\fIRAND_egd_bytes()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
It queries \fBbytes\fR bytes and uses RAND_add(3) to seed the
OpenSSL built-in \s-1PRNG\s0.
This function is more flexible than \fIRAND_egd()\fR.
When only one secret key must
be generated, it is not necessary to request the full amount 255 bytes from
the \s-1EGD\s0 socket. This can be advantageous, since the amount of entropy
that can be retrieved from \s-1EGD\s0 over time is limited.
.SH "NOTES"
.IX Header "NOTES"
On systems without /dev/*random devices providing entropy from the kernel,
the \s-1EGD\s0 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.
.PP
\&\s-1EGD\s0 is available from http://www.lothar.com/tech/crypto/ (\f(CW\*(C`perl
Makefile.PL; make; make install\*(C'\fR to install). It is run as \fBegd\fR
\&\fIpath\fR, where \fIpath\fR is an absolute path designating a socket. When
\&\fIRAND_egd()\fR is called with that path as an argument, it tries to read
random bytes that \s-1EGD\s0 has collected. The read is performed in
non-blocking mode.
.PP
Alternatively, the EGD-interface compatible daemon \s-1PRNGD\s0 can be used. It is
available from
http://www.aet.tu-cottbus.de/personen/jaenicke/postfix_tls/prngd.html .
\&\s-1PRNGD\s0 does employ an internal \s-1PRNG\s0 itself and can therefore never run
out of entropy.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
\&\fIRAND_egd()\fR and \fIRAND_egd_bytes()\fR 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 \s-1PRNG\s0.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
rand(3), RAND_add(3),
RAND_cleanup(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIRAND_egd()\fR is available since OpenSSL 0.9.5.
.PP
\&\fIRAND_egd_bytes()\fR is available since OpenSSL 0.9.6.
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