/usr/man/cat.3/RAND_egd_bytes.3

RAND_egd(3)                  OpenSSL                  RAND_egd(3)

NAME

     RAND_egd, RAND_egd_bytes, RAND_query_egd_bytes - 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.

1.0.2t               Last change: 2019-09-10                    1

RAND_egd(3)                  OpenSSL                  RAND_egd(3)

     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.

1.0.2t               Last change: 2019-09-10                    2

See also RAND_egd(3)
See also RAND_query_egd_bytes(3)