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131 .IX Title "RAND_egd 3"
132 .TH RAND_egd 3 "2017-01-26" "1.0.2k" "OpenSSL"
133 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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138 RAND_egd, RAND_egd_bytes, RAND_query_egd_bytes \- query entropy gathering daemon
140 .IX Header "SYNOPSIS"
142 \& #include <openssl/rand.h>
144 \& int RAND_egd(const char *path);
145 \& 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. \fIRAND_egd()\fR retrieves entropy from the
181 daemon using the daemon's \*(L"non-blocking read\*(R" command which shall
182 be answered immediately by the daemon without waiting for additional
183 entropy to be collected. The write and read socket operations in the
184 communication are blocking.
186 Alternatively, the EGD-interface compatible daemon \s-1PRNGD\s0 can be used. It is
188 http://prngd.sourceforge.net/ .
189 \&\s-1PRNGD\s0 does employ an internal \s-1PRNG\s0 itself and can therefore never run
192 OpenSSL automatically queries \s-1EGD\s0 when entropy is requested via \fIRAND_bytes()\fR
193 or the status is checked via \fIRAND_status()\fR for the first time, if the socket
194 is located at /var/run/egd\-pool, /dev/egd\-pool or /etc/egd\-pool.
196 .IX Header "RETURN VALUE"
197 \&\fIRAND_egd()\fR and \fIRAND_egd_bytes()\fR return the number of bytes read from the
198 daemon on success, and \-1 if the connection failed or the daemon did not
199 return enough data to fully seed the \s-1PRNG.\s0
201 \&\fIRAND_query_egd_bytes()\fR returns the number of bytes read from the daemon on
202 success, and \-1 if the connection failed. The \s-1PRNG\s0 state is not considered.
204 .IX Header "SEE ALSO"
205 \&\fIrand\fR\|(3), \fIRAND_add\fR\|(3),
206 \&\fIRAND_cleanup\fR\|(3)
209 \&\fIRAND_egd()\fR is available since OpenSSL 0.9.5.
211 \&\fIRAND_egd_bytes()\fR is available since OpenSSL 0.9.6.
213 \&\fIRAND_query_egd_bytes()\fR is available since OpenSSL 0.9.7.
215 The automatic query of /var/run/egd\-pool et al was added in OpenSSL 0.9.7.