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RAND_egd(3) OpenSSL RAND_egd(3)
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RAND_egd - query entropy gathering daemon
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);
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).
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-
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. The read is performed in non-blocking mode.
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
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-
openssl_rand(3), RAND_add(3), RAND_cleanup(3)
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
0.9.9-dev 2007-03-06 RAND_egd(3)