NAME    [Toc]    [Back]

       RAND_egd - query entropy gathering daemon

LIBRARY    [Toc]    [Back]

       libcrypto, -lcrypto

SYNOPSIS    [Toc]    [Back]

        #include <openssl/rand.h>

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

DESCRIPTION    [Toc]    [Back]

       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.

NOTES    [Toc]    [Back]

       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-cot-
       tbus.de/personen/jaenicke/postfix_tls/prngd.html .  PRNGD
       does employ an internal PRNG itself and can therefore
       never run out of entropy.

RETURN VALUE    [Toc]    [Back]

       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.

SEE ALSO    [Toc]    [Back]

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

HISTORY    [Toc]    [Back]

       RAND_egd() is available since OpenSSL 0.9.5.

       RAND_egd_bytes() is available since OpenSSL 0.9.6.