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Diffstat (limited to 'openssl/doc/crypto/RAND_egd.pod')
-rw-r--r-- | openssl/doc/crypto/RAND_egd.pod | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/openssl/doc/crypto/RAND_egd.pod b/openssl/doc/crypto/RAND_egd.pod new file mode 100644 index 000000000..8b8c61d16 --- /dev/null +++ b/openssl/doc/crypto/RAND_egd.pod @@ -0,0 +1,88 @@ +=pod + +=head1 NAME + +RAND_egd - query entropy gathering daemon + +=head1 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); + +=head1 DESCRIPTION + +RAND_egd() queries the entropy gathering daemon EGD on socket B<path>. +It queries 255 bytes and uses L<RAND_add(3)|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 B<path>. +It queries B<bytes> bytes and uses L<RAND_add(3)|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 +B<path>. If B<buf> is given, B<bytes> bytes are queried and written into +B<buf>. If B<buf> is NULL, B<bytes> bytes are queried and used to seed the +OpenSSL built-in PRNG using L<RAND_add(3)|RAND_add(3)>. + +=head1 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/ (C<perl +Makefile.PL; make; make install> to install). It is run as B<egd> +I<path>, where I<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. + +=head1 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. + +=head1 SEE ALSO + +L<rand(3)|rand(3)>, L<RAND_add(3)|RAND_add(3)>, +L<RAND_cleanup(3)|RAND_cleanup(3)> + +=head1 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. + +=cut |