1=pod
2
3=head1 NAME
4
5RAND_egd - query entropy gathering daemon
6
7=head1 SYNOPSIS
8
9 #include <openssl/rand.h>
10
11 int RAND_egd(const char *path);
12 int RAND_egd_bytes(const char *path, int bytes);
13
14 int RAND_query_egd_bytes(const char *path, unsigned char *buf, int bytes);
15
16=head1 DESCRIPTION
17
18RAND_egd() queries the entropy gathering daemon EGD on socket B<path>.
19It queries 255 bytes and uses L<RAND_add(3)|RAND_add(3)> to seed the
20OpenSSL built-in PRNG. RAND_egd(path) is a wrapper for
21RAND_egd_bytes(path, 255);
22
23RAND_egd_bytes() queries the entropy gathering daemon EGD on socket B<path>.
24It queries B<bytes> bytes and uses L<RAND_add(3)|RAND_add(3)> to seed the
25OpenSSL built-in PRNG.
26This function is more flexible than RAND_egd().
27When only one secret key must
28be generated, it is not necessary to request the full amount 255 bytes from
29the EGD socket. This can be advantageous, since the amount of entropy
30that can be retrieved from EGD over time is limited.
31
32RAND_query_egd_bytes() performs the actual query of the EGD daemon on socket
33B<path>. If B<buf> is given, B<bytes> bytes are queried and written into
34B<buf>. If B<buf> is NULL, B<bytes> bytes are queried and used to seed the
35OpenSSL built-in PRNG using L<RAND_add(3)|RAND_add(3)>.
36
37=head1 NOTES
38
39On systems without /dev/*random devices providing entropy from the kernel,
40the EGD entropy gathering daemon can be used to collect entropy. It provides
41a socket interface through which entropy can be gathered in chunks up to
42255 bytes. Several chunks can be queried during one connection.
43
44EGD is available from http://www.lothar.com/tech/crypto/ (C<perl
45Makefile.PL; make; make install> to install). It is run as B<egd>
46I<path>, where I<path> is an absolute path designating a socket. When
47RAND_egd() is called with that path as an argument, it tries to read
48random bytes that EGD has collected. RAND_egd() retrieves entropy from the
49daemon using the daemon's "non-blocking read" command which shall
50be answered immediately by the daemon without waiting for additional
51entropy to be collected. The write and read socket operations in the
52communication are blocking.
53
54Alternatively, the EGD-interface compatible daemon PRNGD can be used. It is
55available from
56http://prngd.sourceforge.net/ .
57PRNGD does employ an internal PRNG itself and can therefore never run
58out of entropy.
59
60OpenSSL automatically queries EGD when entropy is requested via RAND_bytes()
61or the status is checked via RAND_status() for the first time, if the socket
62is located at /var/run/egd-pool, /dev/egd-pool or /etc/egd-pool.
63
64=head1 RETURN VALUE
65
66RAND_egd() and RAND_egd_bytes() return the number of bytes read from the
67daemon on success, and -1 if the connection failed or the daemon did not
68return enough data to fully seed the PRNG.
69
70RAND_query_egd_bytes() returns the number of bytes read from the daemon on
71success, and -1 if the connection failed. The PRNG state is not considered.
72
73=head1 SEE ALSO
74
75L<rand(3)|rand(3)>, L<RAND_add(3)|RAND_add(3)>,
76L<RAND_cleanup(3)|RAND_cleanup(3)>
77
78=head1 HISTORY
79
80RAND_egd() is available since OpenSSL 0.9.5.
81
82RAND_egd_bytes() is available since OpenSSL 0.9.6.
83
84RAND_query_egd_bytes() is available since OpenSSL 0.9.7.
85
86The automatic query of /var/run/egd-pool et al was added in OpenSSL 0.9.7.
87
88=cut
89