more on Simson Garfinkel analyses Skype - Open Society Institute

[David Farber <dave () farber net>]

------ Forwarded Message
From: "Jonathan S. Shapiro" <shap () eros-os org>
Date: Fri, 28 Jan 2005 22:03:48 -0500
To: <dave () farber net>
Subject: Re: [IP] I more on Simson Garfinkel analyses Skype - Open Society
Institute

I'm going to attempt to chime in on this, because I think Brad is saying
something that I feel is badly wrong.


The most important element of an encryption scheme is that there must be
some well-founded basis for a well-defined degree of confidence. The
encryption may be well done or poorly done. It may be sufficiently
protective or it may not. The thing is that the user has a right and a
need to know where on the spectrum it falls.

The other alternative is ignorance. The first problem with this is that
*your* bad choices can have the effect of disclosing things that have
negative consequences for someone else! The second problem is that it
describes the majority of real users.

In the case of Skype, the argument Brad is making is simply absurd. The
question is not whether something is better than nothing. The question
is why Skype chose to implement an undocumented and unqualified
proprietary encryption scheme at considerable expense rather than use
one of the many existing schemes that are well known, well
characterized, and free for the taking.

When viewed from a business perspective, the only plausible rationale is
immediately apparent. Skype's objective isn't to protect conversations.
It is to render Skype users a captive audience by impeding
interoperability.

It is hardly a new precedent. I seem to remember AT&T trying to use
allegedly proprietary interfaces to impede the attachment of Tom
Carter's Hush-a-Phone in 1956 or so. Different method, same basic
strategy.


Jonathan Shapiro

On Fri, 2005-01-28 at 20:53 -0500, David Farber wrote:
> ------ Forwarded Message
> From: Brad Templeton <btm () templetons com>
> Organization: http://www.templetons.com/brad
> Date: Fri, 28 Jan 2005 17:22:29 -0800
> To: David Farber <dave () farber net>
> Cc: <daw () cs berkeley edu>, <adam () shostack com>, <simsong () csail mit edu>
> Subject: Re: [IP] Simson Garfinkel analyses Skype - Open Society Institute
>
> > I'm sorry to pick nits, but I have to stand by my statement.  No matter
> > how atrociously bad other systems may be, I don't see any basis for saying
> > that Skype is any better.  It might be better, or it might be just as bad.
> > We don't know.
>
> While I fully agree that one can have much more confidence in a
> security system which can be independently analysed and verified
> as secure, it is exactly the attitude above, common in the security
> community,  which I believe has stopped us from deploying security.
>
> "Some" security, even things like DES (which our own foundation proved
> can be crackable), poorly chosen keys, algorithms with flaws, protocols
> that are vulnerable to men in the middle, and proprietary encryption
> systems -- all of these are often declared to be "no better" than having
> no encryption at all.
>
> And so, people, buying that argument, often give us no encryption at
> all, because encryption is hard to do well, and if people keep telling
> you that you have to do it perfectly or you might as well not bother --
> then people don't bother.
>
> The truth is, most people's threat models are not the same as a security
> consultants.   They accept that if the NSA wants to man-in-the-middle
> them, the NSA is going to succeed.
>
> Skype has resisted basic efforts by skilled reverse engineers to
> look at its protocols.  That doesn't mean they are secure, but it
> does mean they are secure from basic efforts.  If I wanted to listen
> in your your skype call and had a tap on your ethernet, I would at
> least have to put a lot of work into it, and possibly could not do it
> at all.    That is a _lot_ more than what is true with in-the-clear SIP,
> where I could slap a packet sniffer on your net and hear your call fairly
> trivially, and with certainty that I would succeed.
>
> This is, in fact, a huge difference.   Encryption is really about how
> hard you make it for the attacker.  Because above a certain level
> of hardness there are a lot of easier ways into your network and
> computer. 
>
> So yes, let's decry that we can't verify Skype's encryption and must
> take their word that it is resistent to attack.  But let's not promote
> this attitude that it is no better than nothing.
>
> ------ End of Forwarded Message
>
>
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