216 lines
7.4 KiB
Groff
216 lines
7.4 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "RAND_egd 3"
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.TH RAND_egd 3 "2018-03-27" "1.0.2o" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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RAND_egd, RAND_egd_bytes, RAND_query_egd_bytes \- query entropy gathering daemon
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/rand.h>
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\&
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\& int RAND_egd(const char *path);
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\& int RAND_egd_bytes(const char *path, int bytes);
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\&
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\& int RAND_query_egd_bytes(const char *path, unsigned char *buf, int bytes);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIRAND_egd()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
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It queries 255 bytes and uses \fIRAND_add\fR\|(3) to seed the
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OpenSSL built-in \s-1PRNG.\s0 RAND_egd(path) is a wrapper for
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RAND_egd_bytes(path, 255);
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.PP
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\&\fIRAND_egd_bytes()\fR queries the entropy gathering daemon \s-1EGD\s0 on socket \fBpath\fR.
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It queries \fBbytes\fR bytes and uses \fIRAND_add\fR\|(3) to seed the
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OpenSSL built-in \s-1PRNG.\s0
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This function is more flexible than \fIRAND_egd()\fR.
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When only one secret key must
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be generated, it is not necessary to request the full amount 255 bytes from
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the \s-1EGD\s0 socket. This can be advantageous, since the amount of entropy
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that can be retrieved from \s-1EGD\s0 over time is limited.
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.PP
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\&\fIRAND_query_egd_bytes()\fR performs the actual query of the \s-1EGD\s0 daemon on socket
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\&\fBpath\fR. If \fBbuf\fR is given, \fBbytes\fR bytes are queried and written into
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\&\fBbuf\fR. If \fBbuf\fR is \s-1NULL, \s0\fBbytes\fR bytes are queried and used to seed the
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OpenSSL built-in \s-1PRNG\s0 using \fIRAND_add\fR\|(3).
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.SH "NOTES"
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.IX Header "NOTES"
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On systems without /dev/*random devices providing entropy from the kernel,
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the \s-1EGD\s0 entropy gathering daemon can be used to collect entropy. It provides
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a socket interface through which entropy can be gathered in chunks up to
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255 bytes. Several chunks can be queried during one connection.
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.PP
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\&\s-1EGD\s0 is available from http://www.lothar.com/tech/crypto/ (\f(CW\*(C`perl
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Makefile.PL; make; make install\*(C'\fR to install). It is run as \fBegd\fR
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\&\fIpath\fR, where \fIpath\fR is an absolute path designating a socket. When
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\&\fIRAND_egd()\fR is called with that path as an argument, it tries to read
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random bytes that \s-1EGD\s0 has collected. \fIRAND_egd()\fR retrieves entropy from the
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daemon using the daemon's \*(L"non-blocking read\*(R" command which shall
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be answered immediately by the daemon without waiting for additional
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entropy to be collected. The write and read socket operations in the
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communication are blocking.
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.PP
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Alternatively, the EGD-interface compatible daemon \s-1PRNGD\s0 can be used. It is
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available from
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http://prngd.sourceforge.net/ .
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\&\s-1PRNGD\s0 does employ an internal \s-1PRNG\s0 itself and can therefore never run
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out of entropy.
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.PP
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OpenSSL automatically queries \s-1EGD\s0 when entropy is requested via \fIRAND_bytes()\fR
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or the status is checked via \fIRAND_status()\fR for the first time, if the socket
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is located at /var/run/egd\-pool, /dev/egd\-pool or /etc/egd\-pool.
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.SH "RETURN VALUE"
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.IX Header "RETURN VALUE"
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\&\fIRAND_egd()\fR and \fIRAND_egd_bytes()\fR return the number of bytes read from the
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daemon on success, and \-1 if the connection failed or the daemon did not
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return enough data to fully seed the \s-1PRNG.\s0
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.PP
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\&\fIRAND_query_egd_bytes()\fR returns the number of bytes read from the daemon on
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success, and \-1 if the connection failed. The \s-1PRNG\s0 state is not considered.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIrand\fR\|(3), \fIRAND_add\fR\|(3),
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\&\fIRAND_cleanup\fR\|(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIRAND_egd()\fR is available since OpenSSL 0.9.5.
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.PP
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\&\fIRAND_egd_bytes()\fR is available since OpenSSL 0.9.6.
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.PP
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\&\fIRAND_query_egd_bytes()\fR is available since OpenSSL 0.9.7.
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.PP
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The automatic query of /var/run/egd\-pool et al was added in OpenSSL 0.9.7.
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