[Ach] OpenVPN and ACH

L. Aaron Kaplan aaron at lo-res.org
Thu Feb 19 16:51:29 CET 2015

On Feb 19, 2015, at 4:26 PM, Aaron Zauner <azet at azet.org> wrote:

> Hi,
> L. Aaron Kaplan wrote:
>> No, I disagree. Not mentioning OpenVPN and the issues you are seeing 
>> makes the guide *weaker* than having it in there with *clear* warnings.
>> Why? Because people will use OpenVPN *anyway*.
>> No matter if you remove the OpenVPN section or not.
>> Better to have a clear message on this.
> Ok. So how does our guide exactly help people that use OpenVPN anyway?
> Nothing in this document improves the default security as shipped with
> OpenVPN.
> I'm fine with a statement on OpenVPN security in there,
That's what I am saying
> but it should
> clearly state that it does not conform to our security recommendations
> in any way.

I'd reformulate the sentence above: yes, we should write that we do see these concerns (a) b) c) ,....) with OpenVPN.
But *not* mentioning these concerns and just not having any text about OpenVPN is *not* good advice.

> Feel free to commit such a change. I've removed it because
> apparently nobody noticed that this is an issue, neither I nor others
> seem to have reviewed the addition of OpenVPN to the document, the only
> concern was: how to use the IANA syntax for our cipherstring with OpenVPN.
> I do see OpenVPN as a security concern, and have for quite some time.
> There are better alternatives and until this patch is merged I consider
> it utterly broken from a cryptographic point of view - but that's just
> my opinion.
> Current issues with CBC mode in TLS:
> *) Lucky13
> *) implementation issues in various software stacks (bleichenbacher)
> *) BEAST (pretty much HTTP specific but still)
^^^^ and here is what we should have in the guide as considerations.

> ..that's BTW the reason why CBC mode is going to be dropped in TLS 1.3
> (only AEAD modes).
> Aaron

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