1RAND_egd(3)                         OpenSSL                        RAND_egd(3)
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NAME

6       RAND_egd - query entropy gathering daemon
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SYNOPSIS

9        #include <openssl/rand.h>
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11        int RAND_egd(const char *path);
12        int RAND_egd_bytes(const char *path, int bytes);
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14        int RAND_query_egd_bytes(const char *path, unsigned char *buf, int bytes);
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DESCRIPTION

17       RAND_egd() queries the entropy gathering daemon EGD on socket path.  It
18       queries 255 bytes and uses RAND_add(3) to seed the OpenSSL built-in
19       PRNG. RAND_egd(path) is a wrapper for RAND_egd_bytes(path, 255);
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21       RAND_egd_bytes() queries the entropy gathering daemon EGD on socket
22       path.  It queries bytes bytes and uses RAND_add(3) to seed the OpenSSL
23       built-in PRNG.  This function is more flexible than RAND_egd().  When
24       only one secret key must be generated, it is not necessary to request
25       the full amount 255 bytes from the EGD socket. This can be
26       advantageous, since the amount of entropy that can be retrieved from
27       EGD over time is limited.
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29       RAND_query_egd_bytes() performs the actual query of the EGD daemon on
30       socket path. If buf is given, bytes bytes are queried and written into
31       buf. If buf is NULL, bytes bytes are queried and used to seed the
32       OpenSSL built-in PRNG using RAND_add(3).
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NOTES

35       On systems without /dev/*random devices providing entropy from the
36       kernel, the EGD entropy gathering daemon can be used to collect
37       entropy. It provides a socket interface through which entropy can be
38       gathered in chunks up to 255 bytes. Several chunks can be queried
39       during one connection.
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41       EGD is available from http://www.lothar.com/tech/crypto/ ("perl
42       Makefile.PL; make; make install" to install). It is run as egd path,
43       where path is an absolute path designating a socket. When RAND_egd() is
44       called with that path as an argument, it tries to read random bytes
45       that EGD has collected. RAND_egd() retrieves entropy from the daemon
46       using the daemon's "non-blocking read" command which shall be answered
47       immediately by the daemon without waiting for additional entropy to be
48       collected. The write and read socket operations in the communication
49       are blocking.
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51       Alternatively, the EGD-interface compatible daemon PRNGD can be used.
52       It is available from http://prngd.sourceforge.net/ .  PRNGD does employ
53       an internal PRNG itself and can therefore never run out of entropy.
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55       OpenSSL automatically queries EGD when entropy is requested via
56       RAND_bytes() or the status is checked via RAND_status() for the first
57       time, if the socket is located at /var/run/egd-pool, /dev/egd-pool or
58       /etc/egd-pool.
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RETURN VALUE

61       RAND_egd() and RAND_egd_bytes() return the number of bytes read from
62       the daemon on success, and -1 if the connection failed or the daemon
63       did not return enough data to fully seed the PRNG.
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65       RAND_query_egd_bytes() returns the number of bytes read from the daemon
66       on success, and -1 if the connection failed. The PRNG state is not
67       considered.
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SEE ALSO

70       rand(3), RAND_add(3), RAND_cleanup(3)
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HISTORY

73       RAND_egd() is available since OpenSSL 0.9.5.
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75       RAND_egd_bytes() is available since OpenSSL 0.9.6.
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77       RAND_query_egd_bytes() is available since OpenSSL 0.9.7.
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79       The automatic query of /var/run/egd-pool et al was added in OpenSSL
80       0.9.7.
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841.0.1e                            2013-02-11                       RAND_egd(3)