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[dragonfly.git] / secure / lib / libcrypto / man / RAND_egd.3
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129.\" ========================================================================
130.\"
131.IX Title "RAND_egd 3"
aac4ff6f 132.TH RAND_egd 3 "2008-09-06" "0.9.8h" "OpenSSL"
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133.SH "NAME"
134RAND_egd \- query entropy gathering daemon
135.SH "SYNOPSIS"
8b0cefbb 136.IX Header "SYNOPSIS"
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137.Vb 1
138\& #include <openssl/rand.h>
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139.Ve
140.PP
141.Vb 2
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142\& int RAND_egd(const char *path);
143\& int RAND_egd_bytes(const char *path, int bytes);
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144.Ve
145.PP
146.Vb 1
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147\& int RAND_query_egd_bytes(const char *path, unsigned char *buf, int bytes);
148.Ve
149.SH "DESCRIPTION"
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150.IX Header "DESCRIPTION"
151\&\fIRAND_egd()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
152It queries 255 bytes and uses \fIRAND_add\fR\|(3) to seed the
153OpenSSL built-in \s-1PRNG\s0. RAND_egd(path) is a wrapper for
154RAND_egd_bytes(path, 255);
984263bc 155.PP
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156\&\fIRAND_egd_bytes()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
157It queries \fBbytes\fR bytes and uses \fIRAND_add\fR\|(3) to seed the
158OpenSSL built-in \s-1PRNG\s0.
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159This function is more flexible than \fIRAND_egd()\fR.
160When only one secret key must
161be generated, it is not necessary to request the full amount 255 bytes from
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162the \s-1EGD\s0 socket. This can be advantageous, since the amount of entropy
163that can be retrieved from \s-1EGD\s0 over time is limited.
984263bc 164.PP
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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
168OpenSSL built-in \s-1PRNG\s0 using \fIRAND_add\fR\|(3).
984263bc 169.SH "NOTES"
8b0cefbb 170.IX Header "NOTES"
984263bc 171On systems without /dev/*random devices providing entropy from the kernel,
8b0cefbb 172the \s-1EGD\s0 entropy gathering daemon can be used to collect entropy. It provides
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173a socket interface through which entropy can be gathered in chunks up to
174255 bytes. Several chunks can be queried during one connection.
175.PP
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176\&\s-1EGD\s0 is available from http://www.lothar.com/tech/crypto/ (\f(CW\*(C`perl
177Makefile.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
180random bytes that \s-1EGD\s0 has collected. The read is performed in
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181non-blocking mode.
182.PP
8b0cefbb 183Alternatively, the EGD-interface compatible daemon \s-1PRNGD\s0 can be used. It is
984263bc 184available from
edae4a78 185http://prngd.sourceforge.net/ .
8b0cefbb 186\&\s-1PRNGD\s0 does employ an internal \s-1PRNG\s0 itself and can therefore never run
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187out of entropy.
188.PP
8b0cefbb 189OpenSSL automatically queries \s-1EGD\s0 when entropy is requested via \fIRAND_bytes()\fR
984263bc 190or the status is checked via \fIRAND_status()\fR for the first time, if the socket
8b0cefbb 191is located at /var/run/egd\-pool, /dev/egd\-pool or /etc/egd\-pool.
984263bc 192.SH "RETURN VALUE"
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193.IX Header "RETURN VALUE"
194\&\fIRAND_egd()\fR and \fIRAND_egd_bytes()\fR return the number of bytes read from the
984263bc 195daemon on success, and \-1 if the connection failed or the daemon did not
8b0cefbb 196return enough data to fully seed the \s-1PRNG\s0.
984263bc 197.PP
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198\&\fIRAND_query_egd_bytes()\fR returns the number of bytes read from the daemon on
199success, and \-1 if the connection failed. The \s-1PRNG\s0 state is not considered.
984263bc 200.SH "SEE ALSO"
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201.IX Header "SEE ALSO"
202\&\fIrand\fR\|(3), \fIRAND_add\fR\|(3),
203\&\fIRAND_cleanup\fR\|(3)
984263bc 204.SH "HISTORY"
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205.IX Header "HISTORY"
206\&\fIRAND_egd()\fR is available since OpenSSL 0.9.5.
984263bc 207.PP
8b0cefbb 208\&\fIRAND_egd_bytes()\fR is available since OpenSSL 0.9.6.
984263bc 209.PP
8b0cefbb 210\&\fIRAND_query_egd_bytes()\fR is available since OpenSSL 0.9.7.
984263bc 211.PP
8b0cefbb 212The automatic query of /var/run/egd\-pool et al was added in OpenSSL 0.9.7.