[Ach] OpenVPN and ACH

L. Aaron Kaplan aaron at lo-res.org
Thu Feb 19 02:19:10 CET 2015

On Feb 18, 2015, at 9:51 PM, Aaron Zauner <azet at azet.org> wrote:

> Hi,
> Reed Loden wrote:
>> Just to follow-up to what Thomas said...
>> I worry about throwing OpenVPN away so quickly... It's used by *lots* of
>> people and companies, and it's not going away anytime soon. I agree that
>> until they have patches like
>> https://community.openvpn.net/openvpn/ticket/301 landed that it's not
>> going to be viably secure, but I worry about the complete lack of
>> OpenVPN detail that people are going to either use the defaults or use
>> random hardening guides that don't give the entire picture.
> I should have explained in more detail; as soon as this patch is merged
> I'm happy to include it again with a statement that OpenVPN above a
> certain version should be used.
>> I think ACH should continue to mention OpenVPN with warnings about it
>> being insecure until certain features/patches are added. Basically,
>> provide the best possible 'secure' config with what it supports today
>> and continue to evolve that over time as OpenVPN improves. Mention to
>> people the specific things it lacks in order to be properly secure as
>> per ACH standards so they know the risks they are taking by using it.
> Feel free to open a pull request on GitHub for that. But I'd like to
> have discussion on this first. I think in the current state of TLS
> security only supporting CBC mode is a mistake. That's exactly what our
> ciphersuite will do with OpenVPN as is today. OpenVPN also has support
> for other block modes including cipher feedback (CFB) and output
> feedback mode (OFB). These have security problems and are not in TLS
> spec, though.
> I'd suggest keeping OpenVPN out of the document until it supports GCM or
> CCM. A good idea would be to write to upstream (OpenVPN) about those
> patches.

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.

> Aaron
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