Re: [TLS] Another [Well-deserved] attack on TLS CCA

Anders Rundgren <anders.rundgren@telia.com> Tue, 18 June 2013 22:18 UTC

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Date: Wed, 19 Jun 2013 00:17:37 +0200
From: Anders Rundgren <anders.rundgren@telia.com>
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To: Geoffrey Keating <geoffk@geoffk.org>
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Subject: Re: [TLS] Another [Well-deserved] attack on TLS CCA
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On 2013-06-18 23:39, Geoffrey Keating wrote:
> Anders Rundgren <anders.rundgren@telia.com> writes:
> 
>> https://sites.google.com/site/oauthgoog/gnubby
>>
>> Luckily for all users Google didn't select TLS CCA (Client Certificate
>> Authentication) for their coming U2F system; only a moron would base a
>> future consumer authentication system on a scheme that is only suited
>> for VPN tunnels and invisible authentications like as ChannelID.
>>
>> What's missing you may wonder?  Well, how about
>>
>> - Compatibility with web sessions including timeout and logout
> 
> Logout is a client-side function, and occurs (typically) when the user
> logs out of their local session and/or quits their web browser.
> Timeout occurs when the TLS connection is closed due to inactivity
> (typically 60 seconds) and the session resumption token is expired,
> which is up to the server; or, looking at it another way, when the
> user's screen lock triggers due to inactivity.

Yes, but this is not how most web apps work today for good or for worse.

> 
>> - A working credential filtering system
> 
> I think this is mostly due to lack of demand.  I wouldn't say it isn't
> "working", just that as commonly implemented, it isn't very good.

There is a perceived little demand because many organizations who are big
users of consumer-PKI have no voice in the IETF.  I believe these guys
would be slaughtered by the IETF bunch since they don't have exactly the
same "lingo" and probably don't know very much about inner life of TLS.


> I wouldn't list these as the biggest problems when trying to use
> client certificate auth, they can be solved with minor fixes. 

Minor fixes?  I doubt that given the fact that you probably must
do something in both ends.


> The first major obstacle you'll hit is trying to get users enrolled.

Indeed.  Which is why Google made it a part of the U2F plot while the
rest of the industry has nothing to offer except insanely useless crap
like Mozilla's <keygen> and Microsoft's CertEnroll.


> Then there are:
> 
> - Enrolling multiple devices
> - Key rollover
> - Lost devices
> - Shared devices
> - Public access terminals

This can be addressed in due time when you have an enrollment solution.
Before that nothing can happen.


> and all the other things that people don't think about immediately
> when they say "let's replace passwords!"

Google may very well be the only party on the planet who have a chance
making this in reach for the masses.  Microsoft, Banks, Governments
and last but not least, the Card industry, have showed that they cannot.


Anders