1RAND_egd(3)                         OpenSSL                        RAND_egd(3)
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NAME

6       RAND_egd, RAND_egd_bytes, RAND_query_egd_bytes - query entropy
7       gathering daemon
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SYNOPSIS

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

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

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

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

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

74       RAND_egd() is available since OpenSSL 0.9.5.
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76       RAND_egd_bytes() is available since OpenSSL 0.9.6.
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78       RAND_query_egd_bytes() is available since OpenSSL 0.9.7.
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80       The automatic query of /var/run/egd-pool et al was added in OpenSSL
81       0.9.7.
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851.0.2o                            2019-09-10                       RAND_egd(3)
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