References: <1482353691-27088-3-git-send-email-davids@...515...> <1482509264-24550-1-git-send-email-davids@...515...> From: Steffan Karger Message-ID: <7de3ab17-08ff-aeaf-a635-e258339b0197@...1856...> Date: Fri, 23 Dec 2016 20:05:53 +0100 MIME-Version: 1.0 In-Reply-To: <1482509264-24550-1-git-send-email-davids@...515...> Subject: Re: [Openvpn-devel] [PATCH master+v2.4 v2] docs: Further enhance the documentation related to SWEET32 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit To: openvpn-devel@lists.sourceforge.net Hi, On 23-12-16 17:07, David Sommerseth wrote: > 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 > --- > Changes.rst | 6 ++++++ > doc/openvpn.8 | 13 ++++++++++--- > 2 files changed, 16 insertions(+), 3 deletions(-) > > diff --git a/Changes.rst b/Changes.rst > index 8508fa3..df5ccb6 100644 > --- 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 f079799..ddaf0ed 100644 > --- 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 > ACK -Steffan