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Re: Semantics of HTTPS

From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
Date: Tue, 07 Aug 2012 00:18:20 +0100
Message-ID: <502050BC.2020701@cs.tcd.ie>
To: "Adrien W. de Croy" <adrien@qbik.com>
CC: Mark Nottingham <mnot@mnot.net>, Willy Tarreau <w@1wt.eu>, "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>


Some points below on what is a tricky issue but one where I think
the status quo is better than the offered alternatives.

On 08/06/2012 11:39 PM, Adrien W. de Croy wrote:
> I think we need to be clear what we are doing when we apply logic such as
> 1. TLS / HTTPS was not designed for inspection
> 2. therefore any inspection is a hack
> 3. therefore we should not allow/sanitise it
> One could argue that 1. was a design failure (failure to cover all
> requirements), and that it should just be fixed. 
> One could also argue that hacks have as much right to be accepted as
> anything else.  They exist for a purpose.

Yep. To break e2e security. But that's not a very defensible
purpose in an organisation (the IETF) where the e2e argument is
taken seriously.

> The real world REQUIRES inspection capability, for various reasons.

The real world also REQUIRES lawful intercept. But we (the IETF)
don't do that, and we're right I think. (That is, I agree with
our consensus position.)

I'd encourage folks who care about this to go look back at the raven
list arguments (if you've plenty of time;-) [1] I personally think
that was the IETF at its best - deciding a technical position on
a technical basis even in the face of non-trivial political and
commercial pressure.

   [1] http://www.ietf.org/mail-archive/web/raven/current/maillist.html

(I hope folks don't try score points by selective quoting from that
archive - pretty much all opinions are represented there as I recall;-)

> We can either ignore that requirement, and carry on with our arms race,
> or come to some mutual agreement on how to deal with the very real and
> in many (if not most) cases entirely legitimate requirement.
> At the moment, it's starting to look uglier and uglier.  Major sites
> such as FB / Google move to TLS (maybe just to reduce blockage at
> corporate firewalls?).
> I can't count how many customers ask me a week how to block https sites
> esp FB, gmail, youtube and twitter.  It's pointless arguing whether
> someone should do this or not, we don't pay for their staff down-time.
> So we have MITM code in the lab.  Many others have deployed already.

Well just block those sites if you must. I don't see why inspection
is somehow better. I do see that some people might think inspection
is better, but if that's a falsehood then no conclusion can be drawn.
(False => anything, logically.) Evidence of the effectiveness of
MITM inspection (vs. endpoint mechanisms) would be good, but seems
to be missing.

> Next step if a site wants to do something about that is maybe start to
> use client certificates. 
> Anyone here from the TLS WG able to comment on whether there are plans
> to combat MITM in this respect?  

I don't get the question. TLS is designed to combat MITM with or
without client certs. That's a fundamental requirement for TLS.

> It's interesting to see the comment
> about recent TLS WG rejection of support for inspection.

Recent and repeated. I think this is maybe the 3rd time.

> At the end of the day, the requirement is not going away, and it's only
> my opinion, but I think we'd get something that
> a) works a lot better (more reliably)
> b) better reflects reality and allows users to make informed choices

Feel free to propose a specification that meets your proposed
requirements. That is hard-to-impossible IMO.

> if we actually accepted the reality of this requirement and designed for
> it.  IMO b actually results in more security. 
> As for the issue of trust, this results in a requirement to trust the
> proxy. 

You left out an important thing: it requires sites (e.g. a bank)
to trust proxies the site has never heard of with the site's
customer data, e.g. payment information.

Do we really want to engineer the web so as to allow a company
proxy to prevent payments to the company's favourite bad cause?
That's what's being enabled here. Its a bad plan.

It might be tractable to figure how to get a user to trust her
employer's proxy for some things, but that's just nowhere near a
full solution IMO.


>  We don't have a system that does not require any trust in any
> party.  We trust the bank with our money, we trust the CA to properly
> issue certificates and to ensure safe keeping of their private keys. 
> Most people IME are quite happy to have their web surfing scanned for
> viruses.  I don't see a problem with some real estate on a browser
> showing that they are required to trust the proxy they are using, or
> don't go to the site.
> Otherwise you have to inspect the certificate of every secure and
> sensitive site you go to in order to check if it's signed by who you
> expect (e.g. a CA instead of your proxy).  It's completely unrealistic
> to expect users to do that, and history has shown that educating
> end-users about the finer points of security is not easily done.
> Adrien
> ------ Original Message ------
> From: "Mark Nottingham" <mnot@mnot.net>
> To: "Willy Tarreau" <w@1wt.eu>
> Cc: "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>
> Sent: 7/08/2012 9:16:48 a.m.
> Subject: Re: Semantics of HTTPS
>> On 06/08/2012, at 4:14 PM, Willy Tarreau <w@1wt.eu> wrote:
>>>> Right. That's a big change from the semantics of HTTPS today,
>>>> though; right
>>>> now, when I see that, I know that I have end-to-end TLS.
>>> No, you *believe* you do, you really don't know. That's clearly the
>>> problem
>>> with the way it works, man-in-the middle proxies are still able to
>>> intercept
>>> it and to forge certs they sign with their own CA and you have no way
>>> to know
>>> if your communications are snooped or not.
>> It's a really big logical leap from the existence of an attack to
>> changing the fundamental semantics of the URI scheme. And, that's what
>> a MITM proxy is -- it's not legitimate, it's not a recognised role,
>> it's an attack. We shouldn't legitimise it.
>> Cheers,
>> -- 
>> Mark Nottingham
>> http://www.mnot.net/
Received on Monday, 6 August 2012 23:18:48 UTC

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