SSL and Malicious Hardware/Software

[Arcane Jill]

-----Original Message-----
From: owner-cryptography at metzdowd.com [mailto:owner-cryptography at metzdowd.com] 
On Behalf Of Steven M. Bellovin
Sent: 03 May 2008 00:51
To: Arcane Jill
Cc: cryptography at metzdowd.com
Subject: Re: SSL and Malicious Hardware/Software

> > > I can't think of a great way of alerting the user,
> >
> > I would be alerted immediately, because I'm using the Petname Tool
> > Firefox plugin.
> >
> > For an unproxied site, I get a small green window with my own choice
> > of text in it (e.g. "Gmail" if I'm visiting https://mail.google.com).
> > If a proxy were to insert itself in the middle, that window would turn
> > yellow, and the message would change to "(untrusted)".
> >
> Assorted user studies suggest that most users do not notice the color
> of random little windows in their browsers...



The point is that the plugin does not trust the browser's list of installed 
CAs. The only thing it trusts is the fingerprint of the certificate. If the 
fingerprint is one that you, personally, (not your browser), have approved in 
the past, then the plugin is green. If not, the plugin is yellow.

Without this plugin, identifying proxies is hard, because the proxy certificate 
will likely be installed in your browser, so it will just automatically pass 
the usual SSL checks, and will appear to you as an authenticated site. If you 
have an expectation that your web traffic will not be eavesdropped en route, 
then the sudden appearance of a proxy can flout that expectation.

On the other hand, a system which checks /only/ that the certificate 
fingerprint is what you expect it to be does not suffer from the same 
disadvantage. This is a technical difference. There's more to it than just the 
color of the warning sign! (...though I do concede, a Red Alert siren would 
probably get more attention :-) ).

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