another reason to keep ExcludeNodes

[Anon Mus]

----- Original Message -----
From: "Roger Dingledine" <arma at mit.edu <mailto:arma at mit.edu>>
To: <or-talk at freehaven.net <mailto:or-talk at freehaven.net>>
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 
isn't
>  > very popular and only a very small subset of people use it). It just 
needs
>  > 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,
>  --Roger
>

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.