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Re: another reason to keep ExcludeNodes

----- Original Message -----
From: "Roger Dingledine" <arma@xxxxxxx <mailto:arma@xxxxxxx>>
To: <or-talk@xxxxxxxxxxxxx <mailto:or-talk@xxxxxxxxxxxxx>>
Sent: Tuesday, February 17, 2009 8:04 PM
Subject: Re: another reason to keep ExcludeNodes

 On Tue, Feb 17, 2009 at 08:08:19PM +0100, Lexi Pimenidis wrote:
> > > little bit of investigation it turned out that one particular
relay was
 > > > always in a circuit that truncated those files, so I added it to my
 > > > ExcludeNodes list.  And voila' complete images from then on.
 > >
 > > Would not it be better if you would report this node so that its
 > > problem can be fixed?
> This could possibly be used to identify anonymous surfers: imagine
an $evil
> exit node trying to identify somebody surfing on $evil-site1 (which
> very popular and only a very small subset of people use it). It just
> to modify the output a bit and then wait for somebody to complain
about it.
> Chances are, the one complaining might give away enough info to
identify himself..?

 Hey, that brings up another possible attack. What if a website keeps
 giving out partial pages in response to exit nodes that it doesn't like
 (for example because it can't monitor them), to encourage users to
 manually mark them as excludeexit, thus making sure that user won't use
 those exits for other sites either?

From my experience there are (probably) govnt run sites in the US which do block a wide range of tor exit nodes. But they permit a few exit nodes, mainly from the US, to have full access.

So this is done whether or not you use excludeexit.

 It wouldn't break anonymity outright, but it would certainly make the
 probabilities more complex to reason about.

 Rabbit holes within rabbit holes,

My experience of excluding nodes (exits or otherwise) is that there are generally plenty of nodes out there so as to keep you safe. And that in general terms only a few exit nodes are a problem at the moment.

Therefore I reckon that the ExcludeNodes, etc, options are very useful - we need them - place a "warning" label on their use if need be.