Re: [TLS] Implementing https://svn.resiprocate.org/rep/ietf-drafts/ekr/draft-rescorla-tls-renegotiate.txt

[Eric Rescorla <[e-mail]>]

At Wed, 11 Nov 2009 18:59:33 +0000,
Dr Stephen Henson wrote:
> 
> [e-mail] wrote:
> > Eric Rescorla wrote:
> > 
> >> I don't think the problem here is really the code point assignment.
> >>
> >> I would imagine the IESG and IANA to be pretty good about doing
> >> advance assignments once the WG has converged on the exact contents
> >> of the extension. I know we had pretty good consensus within a
> >> smaller group, but if when we run it by some cryptographers they say
> >> it's insecure we'll need to change it, at which point it won't
> >> really help to have deployed code with the "early" code point.
> > 
> > <wearing area director hat>
> > 
> > I think this is one of those cases where an exception to the usual
> > procedures might be in order, but the "once the WG has converged on
> > the exact contents" is an important point here. It's relatively rare
> > that the -00 version of some internet draft and the final RFC are
> > actually interoperable.
> > 
> > Using the same extension number for multiple incompatible versions of
> > the draft is probably not a good idea (and probably not very secure,
> > either -- if the handshake fails, you don't know if it's due to an
> > attack or just interoperability problem, and the latter might be much
> > more likely), and I'd like to avoid allocating multiple extension
> > numbers for different versions of the draft, too.
> > 
> 
> Would including a version number in the extension help? Then if the format does
> change implementations can indicate that it is a version they don't support or
> decide they are willing to support an older version.
> 
> This would also cover the case where some cryptographic attack is found against
> the current form later. We keep the extension number but bump up the version.

I considered that, but I'm not sure it really helps. Once the initial version
is widely supported you need to send the old version as well as the new
version for a smooth transition. Might as well have two extension code
points.

-Ekr