/usr/man2/cat.3/RAND_egd_bytes.3.Z(/usr/man2/cat.3/RAND_egd_bytes.3.Z)

NAME

       RAND_egd, RAND_egd_bytes, RAND_query_egd_bytes - query entropy gather-
       ing 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 advanta-
       geous, 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 ker-
       nel, 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 con-
       nection.

       EGD is available from http://www.lothar.com/tech/crypto/ ("perl Make-
       file.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 con-
       sidered.

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                            2019-09-10                       RAND_egd(3)
See also RAND_egd(3)
See also RAND_query_egd_bytes(3)