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. 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.