RAND_egd_bytes (3)

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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 on socket path. It queries 255 bytes and uses RAND_add(3) to seed the OpenSSL built-in RAND_egd(path) is a wrapper for RAND_egd_bytes(path, 255);

RAND_egd_bytes() queries the entropy gathering daemon

on socket path. It queries bytes bytes and uses RAND_add(3) to seed the OpenSSL built-in 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 socket. This can be advantageous, since the amount of entropy that can be retrieved from over time is limited.

RAND_query_egd_bytes() performs the actual query of the

daemon on socket path. If buf is given, bytes bytes are queried and written into buf. If buf is bytes bytes are queried and used to seed the OpenSSL built-in using RAND_add(3).

NOTES

On systems without /dev/*random devices providing entropy from the kernel, the 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.

is available from 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 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

can be used. It is available from prngd.sourceforge.net . does employ an internal itself and can therefore never run out of entropy.

OpenSSL automatically queries

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

RAND_query_egd_bytes() returns the number of bytes read from the daemon on success, and -1 if the connection failed. The

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.