docs: Further enhance the documentation related to SWEET32

The git master/2.4 code lacked some useful information about
the changes to --reneg-bytes, SWEET32 and weak ciphers (less
than 128-bits cipher blocks)

v2 - Fixed a couple of grammar/typo issues

Signed-off-by: David Sommerseth <davids@openvpn.net>
Acked-by: Steffan Karger <steffan@karger.me>
Message-Id: <1482509264-24550-1-git-send-email-davids@openvpn.net>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg13682.html

diff --git a/Changes.rst b/Changes.rst
index 8508fa3fa4d2c6f485eccc0c2dc002f2b5844126..df5ccb631a21c628ec8e9a3a54024551a06f100c 100644 (file)
--- a/Changes.rst
+++ b/Changes.rst
@@ -182,6 +182,12 @@ Deprecated features
 
 User-visible Changes
 --------------------
+- When using ciphers with cipher blocks less than 128-bits
+  OpenVPN will complain loudly if the configuration uses ciphers considered
+  weak, such as the SWEET32 attack vector.  In such scenarios, OpenVPN will by
+  default do a renegotiation for each 64MB of transported data (``--reneg-bytes``).
+  This renegotiation can be disabled, but is HIGHLY DISCOURAGED.
+
 - For certificate DNs with duplicate fields, e.g. "OU=one,OU=two", both fields
   are now exported to the environment, where each second and later occurrence
   of a field get _$N appended to it's field name, starting at N=1.  For the

diff --git a/doc/openvpn.8 b/doc/openvpn.8
index b1ca9ed9cf7a6b95c07ff893a04eb40097f5f78f..b1bb39c720c853044bb8d25c0fc52b808ba0e48a 100644 (file)
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -4876,11 +4876,18 @@ such as TCP expect this role to be left to them.
 .B \-\-reneg\-bytes n
 Renegotiate data channel key after
 .B n
-bytes sent or received (disabled by default).
+bytes sent or received (disabled by default with an exception, see below).
 OpenVPN allows the lifetime of a key
-to be expressed as a number of bytes encrypted/decrypted, a number of packets, or
-a number of seconds.  A key renegotiation will be forced
+to be expressed as a number of bytes encrypted/decrypted, a number of packets,
+or a number of seconds.  A key renegotiation will be forced
 if any of these three criteria are met by either peer.
+
+If using ciphers with cipher block sizes less than 128-bits, \-\-reneg\-bytes is
+set to 64MB by default, unless it is explicitly disabled by setting the value to
+0, but this is
+.B HIGHLY DISCOURAGED
+as this is designed to add some protection against the SWEET32 attack vector.
+For more information see the \-\-cipher option.
 .\"*********************************************************
 .TP
 .B \-\-reneg\-pkts n