[ejabberd] XMPP per-host certs

Peter Saint-Andre stpeter at stpeter.im
Mon Feb 11 20:25:51 MSK 2008

Jesse Thompson wrote:
> Peter Saint-Andre wrote:
>> Brian Cully wrote:
>>> On 8-Feb-2008, at 17:43, Peter Saint-Andre wrote:
>>>> Some clients (iChat etc.) let you specify that the hostname handling a
>>>> gmail.com or googlemail.com (etc.) JID is "talk.google.com". Then when
>>>> you're presented with a certificate for talk.google.com, the client
>>>> considers that to be acceptable. I'll be modifying the  
>>>> specifications to
>>>> make it clear that this approach is one allowable authentication flow.
>>> 	I assume this is true for SRV record lookup as well? 
>> As you might imagine, the IETF security mafia considers the results of
>> SRV lookups to be less than fully reliable, at least in the absence of
>> DNSSEC. Naturally, end users can be unreliable too (who convinced them
>> to input "talk.google.com" as acceptable for gmail.com?).
> My opinion is that if the DKIM authors aren't that worried about DNS
> poisoning, then it probably isn't a big concern for XMPP.  If DNS
> poisoning becomes a problem, then SRV record forging will be the least
> of our problems, and DNSSEC will become a major priority.
> The IETF security's approach is akin to telling you to wear a bullet
> proof vest whenever you leave your house.  Yes, it will make you more
> secure, but it's not really necessary.

Heh. Well, we work within that framework becauuse XMPP is an IETF
technology, but I agree we need to make our usage profiles apply to the
real world, too. It's a delicate balance. :)

>>> I'd be curious  
>>> about experience w/ Psi, Adium, and iChat, if anyone happens to know.
>> Different clients handle certificates in different ways. Harmonizing the
>> user experience across clients sounds like a good goal for 2008 and beyond.
> If this problem is to be resolved purely on the client side, then I
> think iChat and Adium have implemented the correct approach to the problem.
> Some clients (Psi) force the user to disable all SSL warnings, which
> makes things less secure.  I think that this is the worst approach to
> the problem.

Yes, that doesn't seem like the right approach. I'll chat with the Psi
developers about that.

> Other clients (Pidgin, Gajim, Meebo) ignore hostname mismatches, and I
> can't tell what other certificate errors they also ignore.  Obviously,
> they've sacrificed some security for usability.
> It would be the most desirable user experience if the client would never
> have to prompt the user if it doesn't have to.  It would be nice if the
> specifications defined the conditions which a client could trust a
> mismatched domain certificate without prompting the user.

Yes, that's what I'm working towards.


Peter Saint-Andre

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