Re: [TLS] Summarizing identity change discussion so far

[Stephen Farrell <[e-mail]>]

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.

[e-mail] 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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