RAND_egd(3) - phpMan

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.

       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.



1.0.2k                                      2017-01-26                                RAND_egd(3)

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