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89 lines
3.2 KiB
Plaintext
89 lines
3.2 KiB
Plaintext
=pod
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=head1 NAME
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RAND_egd - query entropy gathering daemon
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=head1 SYNOPSIS
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#include <openssl/rand.h>
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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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int RAND_query_egd_bytes(const char *path, unsigned char *buf, int bytes);
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=head1 DESCRIPTION
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RAND_egd() queries the entropy gathering daemon EGD on socket B<path>.
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It queries 255 bytes and uses L<RAND_add(3)|RAND_add(3)> to seed the
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OpenSSL built-in PRNG. RAND_egd(path) is a wrapper for
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RAND_egd_bytes(path, 255);
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RAND_egd_bytes() queries the entropy gathering daemon EGD on socket B<path>.
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It queries B<bytes> bytes and uses L<RAND_add(3)|RAND_add(3)> to seed the
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OpenSSL built-in PRNG.
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This function is more flexible than RAND_egd().
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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 EGD socket. This can be advantageous, since the amount of entropy
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that can be retrieved from EGD over time is limited.
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RAND_query_egd_bytes() performs the actual query of the EGD daemon on socket
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B<path>. If B<buf> is given, B<bytes> bytes are queried and written into
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B<buf>. If B<buf> is NULL, B<bytes> bytes are queried and used to seed the
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OpenSSL built-in PRNG using L<RAND_add(3)|RAND_add(3)>.
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=head1 NOTES
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On systems without /dev/*random devices providing entropy from the kernel,
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the EGD 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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EGD is available from http://www.lothar.com/tech/crypto/ (C<perl
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Makefile.PL; make; make install> to install). It is run as B<egd>
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I<path>, where I<path> is an absolute path designating a socket. When
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RAND_egd() is called with that path as an argument, it tries to read
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random bytes that EGD has collected. RAND_egd() retrieves entropy from the
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daemon using the daemon's "non-blocking read" 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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Alternatively, the EGD-interface compatible daemon PRNGD can be used. It is
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available from
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http://prngd.sourceforge.net/ .
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PRNGD does employ an internal PRNG itself and can therefore never run
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out of entropy.
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OpenSSL automatically queries EGD when entropy is requested via RAND_bytes()
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or the status is checked via RAND_status() 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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=head1 RETURN VALUE
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RAND_egd() and RAND_egd_bytes() 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 PRNG.
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RAND_query_egd_bytes() returns the number of bytes read from the daemon on
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success, and -1 if the connection failed. The PRNG state is not considered.
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=head1 SEE ALSO
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L<rand(3)|rand(3)>, L<RAND_add(3)|RAND_add(3)>,
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L<RAND_cleanup(3)|RAND_cleanup(3)>
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=head1 HISTORY
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RAND_egd() is available since OpenSSL 0.9.5.
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RAND_egd_bytes() is available since OpenSSL 0.9.6.
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RAND_query_egd_bytes() is available since OpenSSL 0.9.7.
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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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=cut
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