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124 .\" ========================================================================
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126 .IX Title "RAND_egd 3"
127 .TH RAND_egd 3 "2007-10-24" "0.9.8g" "OpenSSL"
128 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
129 .\" way too many mistakes in technical documents.
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131 .nh
132 .SH "NAME"
133 RAND_egd \- query entropy gathering daemon
134 .SH "SYNOPSIS"
135 .IX Header "SYNOPSIS"
136 .Vb 1
137 \& #include <openssl/rand.h>
138 \&
139 \& int RAND_egd(const char *path);
140 \& int RAND_egd_bytes(const char *path, int bytes);
141 \&
142 \& int RAND_query_egd_bytes(const char *path, unsigned char *buf, int bytes);
143 .Ve
144 .SH "DESCRIPTION"
145 .IX Header "DESCRIPTION"
146 \&\fIRAND_egd()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
147 It queries 255 bytes and uses \fIRAND_add\fR\|(3) to seed the
148 OpenSSL built-in \s-1PRNG\s0. RAND_egd(path) is a wrapper for
149 RAND_egd_bytes(path, 255);
150 .PP
151 \&\fIRAND_egd_bytes()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
152 It queries \fBbytes\fR bytes and uses \fIRAND_add\fR\|(3) to seed the
153 OpenSSL built-in \s-1PRNG\s0.
154 This function is more flexible than \fIRAND_egd()\fR.
155 When only one secret key must
156 be generated, it is not necessary to request the full amount 255 bytes from
157 the \s-1EGD\s0 socket. This can be advantageous, since the amount of entropy
158 that can be retrieved from \s-1EGD\s0 over time is limited.
159 .PP
160 \&\fIRAND_query_egd_bytes()\fR performs the actual query of the \s-1EGD\s0 daemon on socket
161 \&\fBpath\fR. If \fBbuf\fR is given, \fBbytes\fR bytes are queried and written into
162 \&\fBbuf\fR. If \fBbuf\fR is \s-1NULL\s0, \fBbytes\fR bytes are queried and used to seed the
163 OpenSSL built-in \s-1PRNG\s0 using \fIRAND_add\fR\|(3).
164 .SH "NOTES"
165 .IX Header "NOTES"
166 On systems without /dev/*random devices providing entropy from the kernel,
167 the \s-1EGD\s0 entropy gathering daemon can be used to collect entropy. It provides
168 a socket interface through which entropy can be gathered in chunks up to
169 255 bytes. Several chunks can be queried during one connection.
170 .PP
171 \&\s-1EGD\s0 is available from http://www.lothar.com/tech/crypto/ (\f(CW\*(C`perl
172 Makefile.PL; make; make install\*(C'\fR to install). It is run as \fBegd\fR
173 \&\fIpath\fR, where \fIpath\fR is an absolute path designating a socket. When
174 \&\fIRAND_egd()\fR is called with that path as an argument, it tries to read
175 random bytes that \s-1EGD\s0 has collected. The read is performed in
176 non-blocking mode.
177 .PP
178 Alternatively, the EGD-interface compatible daemon \s-1PRNGD\s0 can be used. It is
179 available from
180 http://prngd.sourceforge.net/ .
181 \&\s-1PRNGD\s0 does employ an internal \s-1PRNG\s0 itself and can therefore never run
182 out of entropy.
183 .PP
184 OpenSSL automatically queries \s-1EGD\s0 when entropy is requested via \fIRAND_bytes()\fR
185 or the status is checked via \fIRAND_status()\fR for the first time, if the socket
186 is located at /var/run/egd\-pool, /dev/egd\-pool or /etc/egd\-pool.
187 .SH "RETURN VALUE"
188 .IX Header "RETURN VALUE"
189 \&\fIRAND_egd()\fR and \fIRAND_egd_bytes()\fR return the number of bytes read from the
190 daemon on success, and \-1 if the connection failed or the daemon did not
191 return enough data to fully seed the \s-1PRNG\s0.
192 .PP
193 \&\fIRAND_query_egd_bytes()\fR returns the number of bytes read from the daemon on
194 success, and \-1 if the connection failed. The \s-1PRNG\s0 state is not considered.
195 .SH "SEE ALSO"
196 .IX Header "SEE ALSO"
197 \&\fIrand\fR\|(3), \fIRAND_add\fR\|(3),
198 \&\fIRAND_cleanup\fR\|(3)
199 .SH "HISTORY"
200 .IX Header "HISTORY"
201 \&\fIRAND_egd()\fR is available since OpenSSL 0.9.5.
202 .PP
203 \&\fIRAND_egd_bytes()\fR is available since OpenSSL 0.9.6.
204 .PP
205 \&\fIRAND_query_egd_bytes()\fR is available since OpenSSL 0.9.7.
206 .PP
207 The automatic query of /var/run/egd\-pool et al was added in OpenSSL 0.9.7.