Re: [TLS] Summarizing identity change discussion so far

The security considerations section of this draft has to describe the
fact that even with this fix, renegotiation does things that will
surprise application developers, and can cause security
vulnerabilities for some of them.

That part we cannot avoid -- some text has to be included.

It's not absolutely required that the text makes recommendations how
to avoid those vulnerabilities, but IMHO it would be a bit strange to
just describe the security problem without saying anything how to
avoid it...

Best regards,
Pasi

> -----Original Message-----
> From: ext Stephen Farrell [mailto:stephen.farrell@cs.tcd.ie]
> Sent: 08 December, 2009 15:01
> To: Eronen Pasi (Nokia-NRC/Helsinki)
> Cc: tls@ietf.org
> Subject: Re: [TLS] Summarizing identity change discussion so far
> 
> 
> Hi Pasi,
> 
> I think that all sounds ok, except I don't see any mention
> in your summary of the fact that a bunch of people (incl. me)
> said that this just shouldn't be part of the re-negotiation
> fix. Maybe some of those have changed their minds as a result
> of the discussion though, I've not checked.
> 
> If the consensus ends up being to include some text about
> this, then your approach below sounds ok to me, (though
> I'd be a bit worried it might take a while to get the
> right text), but I'd still rather leave it out entirely
> and have some other document address the identity-change
> issue in a more considered manner.
> 
> S.
> 
> Pasi.Eronen@nokia.com wrote:
> > (wearing Area Director hat)
> >
> > Although the IETF Last Call is still underway, here's a short attempt
> > to summarize the discussion regarding identity changes (Section 7) so
> > far:
> >
> > - We seem to agree that changing the certificate/identity
> > during secure renegotiation (so there's no man-in-the-middle, just
> two
> > parties) could confuse some applications.  James Manger's email
> provides
> > IMHO a good example of what that confusion could be (in this
> particular
> > example, the confusion has security implications, too):
> >
> > http://www.ietf.org/mail-archive/web/tls/current/msg05122.html
> >
> > - We mostly seem to agree that some applications could not just
> handle
> > certificate/identity changes correctly, but would actually benefit
> > from them.
> >
> > - We seem to agree that it would be a reasonable idea for the TLS
> > library to offer the applications an option where the TLS library
> > checks that the certificate doesn't change during renegotiation.
> > This is an *option* -- an application could decide not to use it,
> > and e.g. do more complex comparisons.
> >
> > - We have much less support for requiring that every TLS library
> > MUST implement this functionality and/or MUST enable it by default
> > (whatever "by default" means in your API), at least in this draft.
> >
> > Unless I'm badly misreading the situation, or it significantly
> changes
> > during the rest of the IETF Last Call, my proposal here would be as
> > follows:
> >
> > - We do NOT require (with "MUST") any changes to TLS libraries in
> this
> > regard.
> >
> > - We describe the situation a bit more clearly than the current text
> > does (it seems many people found the current text somewhat unclear).
> >
> > - We recommend that TLS libraries SHOULD provide identity matching
> > (with memcmp, abort handshake if changed) functionality to
> > applications, and SHOULD allow applications to enable/disable this
> > functionality.
> >
> > - We include a sentence or two describing the pros and cons of
> > enabling/not enabling this feature by default, but don't require or
> > recommend any particular default value.
> >
> > - The text probably needs to note that if the applications wants to
> > deal with identity changes, it may need to consider the "which
> > application_data byte(s) correspond to which identity" question (or
> it
> > may not -- the answer may depend a lot on the application protocol).
> >
> > Does this sound like a reasonable approach?
> >
> > Best regards,
> > Pasi
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