RAND_egd

RAND_egd(3)                          OpenSSL                         RAND_egd(3)



NAME
       RAND_egd, RAND_egd_bytes, RAND_query_egd_bytes - query entropy gathering
       daemon

SYNOPSIS
        #include <openssl/rand.h>

        int RAND_egd(const char *path);
        int RAND_egd_bytes(const char *path, int bytes);

        int RAND_query_egd_bytes(const char *path, unsigned char *buf, int bytes);

DESCRIPTION
       RAND_egd() queries the entropy gathering daemon EGD on socket path.  It
       queries 255 bytes and uses RAND_add(3) to seed the OpenSSL built-in PRNG.
       RAND_egd(path) is a wrapper for RAND_egd_bytes(path, 255);

       RAND_egd_bytes() queries the entropy gathering daemon EGD on socket path.
       It queries bytes bytes and uses RAND_add(3) to seed the OpenSSL built-in
       PRNG.  This function is more flexible than RAND_egd().  When only one
       secret key must be generated, it is not necessary to request the full
       amount 255 bytes from the EGD socket. This can be advantageous, since the
       amount of entropy that can be retrieved from EGD over time is limited.

       RAND_query_egd_bytes() performs the actual query of the EGD daemon on
       socket path. If buf is given, bytes bytes are queried and written into
       buf. If buf is NULL, bytes bytes are queried and used to seed the OpenSSL
       built-in PRNG using RAND_add(3).

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(3), RAND_add(3), RAND_cleanup(3)

HISTORY
       RAND_egd() is available since OpenSSL 0.9.5.

       RAND_egd_bytes() is available since OpenSSL 0.9.6.

       RAND_query_egd_bytes() is available since OpenSSL 0.9.7.

       The automatic query of /var/run/egd-pool et al was added in OpenSSL
       0.9.7.



1.0.2t                             2019-09-10                        RAND_egd(3)