NAME    [Toc]    [Back]

       RAND_egd - Query entropy gathering daemon

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]

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

       The  RAND_egd_bytes() function queries the entropy gathering
 daemon EGD on socket path. It queries bytes  and  uses
       RAND_add()  to  seed the OpenSSL built-in PRNG. This function
 is more flexible than the RAND_egd() function .  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 the RAND_egd() function is called  with
       that  path  as  an argument, it tries to read random bytes
       that EGD 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]

       The  RAND_egd()  and RAND_egd_bytes() functions 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.

HISTORY    [Toc]    [Back]

       The RAND_egd() function is available since OpenSSL  0.9.5.

       The  RAND_egd_bytes()  function is available since OpenSSL
       0.9.6.

SEE ALSO    [Toc]    [Back]

       Functions: rand_ssl(3), RAND_add(3), RAND_cleanup(3)



                                                      RAND_egd(3)