Update documentation to match the state at 0.9.6 _and_ the recent changes.

[openssl.git] / doc / crypto / RAND_egd.pod

diff --git a/doc/crypto/RAND_egd.pod b/doc/crypto/RAND_egd.pod
index a40bd96198861e3259eadefeb229f8de9d44a302..f66c3091b9aed6052585e32b8b34fe831927da41 100644 (file)
--- a/doc/crypto/RAND_egd.pod
+++ b/doc/crypto/RAND_egd.pod
@@ -9,10 +9,38 @@ RAND_egd - query entropy gathering daemon
  #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.
+
+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.
+
+While RAND_egd() is longer available (see HISTORY section), the
+RAND_egd_bytes() function is more flexible. When only one secret key must
+be generated, it is not needed 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.
 
 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>
@@ -21,18 +49,32 @@ 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://www.aet.tu-cottbus.de/personen/jaenicke/postfix_tls/prngd.html .
+PRNGD does employ an internal PRNG itself and can therefore never run
+out of entropy.
+
 =head1 RETURN VALUE
 
-RAND_egd() returns 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_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)>
+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.
+
 =cut