RAND_egd(3)                 OpenSSL                 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 dae-
       mon 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 des-
       ignating 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-cot-
       tbus.de/personen/jaenicke/postfix_tls/prngd.html .
       PRNGD does employ an internal PRNG itself and can there-
       fore 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.



0.9.7c                     2001-02-10               RAND_egd(3)
