NOTES
On systems without /dev/*random devices providing entropy from the kernel, the EGD entropy gathering daemon can be used to collect entropy. It provides a socket interface through which entropy can be gathered in chunks up to 255 bytes. Several chunks can be queried during one connection.
EGD is available from http://www.lothar.com/tech/crypto/ (perl Makefile.PL; make; make install to install). It is run as egd path, where path is an absolute path designating a socket. When RAND_egd() is called with that path as an argument, it tries to read random bytes that EGD has collected. RAND_egd() retrieves entropy from the daemon using the daemon's "non-blocking read" command which shall be answered immediately by the daemon without waiting for additional entropy to be collected. The write and read socket operations in the communication are blocking.
Alternatively, the EGD-interface compatible daemon PRNGD can be used. It is available from http://prngd.sourceforge.net/ . PRNGD does employ an internal PRNG itself and can therefore never run out of entropy.
OpenSSL automatically queries EGD when entropy is requested via RAND_bytes() or the status is checked via RAND_status() for the first time, if the socket is located at /var/run/egd-pool, /dev/egd-pool or /etc/egd-pool.
RETURN VALUE
RAND_egd() and RAND_egd_bytes() return the number of bytes read from the daemon on success, and -1 if the connection failed or the daemon did not return enough data to fully seed the PRNG.
RAND_query_egd_bytes() returns the number of bytes read from the daemon on success, and -1 if the connection failed. The PRNG state is not considered.
SEE ALSO
RAND_add(3), COPYRIGHT
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Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.