RAND_egd(3)

     NAME
          RAND_egd - 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. The read is performed in non-blocking mode.

          Alternatively, the EGD-interface compatible daemon PRNGD can
          be used. It is available from http://www.aet.tu-
          cottbus.de/personen/jaenicke/postfix_tls/prngd.html .  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.