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131 .IX Title "RAND_egd 3"
132 .TH RAND_egd 3 "2005-02-24" "0.9.7d" "OpenSSL"
134 RAND_egd \- query entropy gathering daemon
136 .IX Header "SYNOPSIS"
138 \& #include <openssl/rand.h>
142 \& int RAND_egd(const char *path);
143 \& int RAND_egd_bytes(const char *path, int bytes);
147 \& int RAND_query_egd_bytes(const char *path, unsigned char *buf, int bytes);
150 .IX Header "DESCRIPTION"
151 \&\fIRAND_egd()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
152 It queries 255 bytes and uses \fIRAND_add\fR\|(3) to seed the
153 OpenSSL built-in \s-1PRNG\s0. RAND_egd(path) is a wrapper for
154 RAND_egd_bytes(path, 255);
156 \&\fIRAND_egd_bytes()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
157 It queries \fBbytes\fR bytes and uses \fIRAND_add\fR\|(3) to seed the
158 OpenSSL built-in \s-1PRNG\s0.
159 This function is more flexible than \fIRAND_egd()\fR.
160 When only one secret key must
161 be generated, it is not necessary to request the full amount 255 bytes from
162 the \s-1EGD\s0 socket. This can be advantageous, since the amount of entropy
163 that can be retrieved from \s-1EGD\s0 over time is limited.
165 \&\fIRAND_query_egd_bytes()\fR performs the actual query of the \s-1EGD\s0 daemon on socket
166 \&\fBpath\fR. If \fBbuf\fR is given, \fBbytes\fR bytes are queried and written into
167 \&\fBbuf\fR. If \fBbuf\fR is \s-1NULL\s0, \fBbytes\fR bytes are queried and used to seed the
168 OpenSSL built-in \s-1PRNG\s0 using \fIRAND_add\fR\|(3).
171 On systems without /dev/*random devices providing entropy from the kernel,
172 the \s-1EGD\s0 entropy gathering daemon can be used to collect entropy. It provides
173 a socket interface through which entropy can be gathered in chunks up to
174 255 bytes. Several chunks can be queried during one connection.
176 \&\s-1EGD\s0 is available from http://www.lothar.com/tech/crypto/ (\f(CW\*(C`perl
177 Makefile.PL; make; make install\*(C'\fR to install). It is run as \fBegd\fR
178 \&\fIpath\fR, where \fIpath\fR is an absolute path designating a socket. When
179 \&\fIRAND_egd()\fR is called with that path as an argument, it tries to read
180 random bytes that \s-1EGD\s0 has collected. The read is performed in
183 Alternatively, the EGD-interface compatible daemon \s-1PRNGD\s0 can be used. It is
185 http://www.aet.tu\-cottbus.de/personen/jaenicke/postfix_tls/prngd.html .
186 \&\s-1PRNGD\s0 does employ an internal \s-1PRNG\s0 itself and can therefore never run
189 OpenSSL automatically queries \s-1EGD\s0 when entropy is requested via \fIRAND_bytes()\fR
190 or the status is checked via \fIRAND_status()\fR for the first time, if the socket
191 is located at /var/run/egd\-pool, /dev/egd\-pool or /etc/egd\-pool.
193 .IX Header "RETURN VALUE"
194 \&\fIRAND_egd()\fR and \fIRAND_egd_bytes()\fR return the number of bytes read from the
195 daemon on success, and \-1 if the connection failed or the daemon did not
196 return enough data to fully seed the \s-1PRNG\s0.
198 \&\fIRAND_query_egd_bytes()\fR returns the number of bytes read from the daemon on
199 success, and \-1 if the connection failed. The \s-1PRNG\s0 state is not considered.
201 .IX Header "SEE ALSO"
202 \&\fIrand\fR\|(3), \fIRAND_add\fR\|(3),
203 \&\fIRAND_cleanup\fR\|(3)
206 \&\fIRAND_egd()\fR is available since OpenSSL 0.9.5.
208 \&\fIRAND_egd_bytes()\fR is available since OpenSSL 0.9.6.
210 \&\fIRAND_query_egd_bytes()\fR is available since OpenSSL 0.9.7.
212 The automatic query of /var/run/egd\-pool et al was added in OpenSSL 0.9.7.