Date: Wed, 3 Jul 2013 10:54:09 -0500
From: Michael T <mt2410689@...il.com>
To: Georgi Guninski <guninski@...inski.com>
Cc: "full-disclosure@...ts.grok.org.uk" <full-disclosure@...ts.grok.org.uk>
Subject: Re: tor vulnerabilities?

What about keysigning among tor operators?  I trust top_op1, and he trusts
top_op2, 3, and 4, so I can trust them as well.

Mike
//Not my areas of expertise

On Wed, Jul 3, 2013 at 9:34 AM, Georgi Guninski <guninski@...inski.com>wrote:

> Valdis,
>
> I see no reason to trust tor.
>
> How do you disprove that at least (say) 42% of the tor network
> is malicious, trying to deanonymize everyone and logging
> everything?
>
> Or maybe some obscure feature deanonymize in O(1) :)
>
>
> On Sat, Jun 29, 2013 at 08:05:17PM -0400, Valdis.Kletnieks@...edu wrote:
> > On Fri, 28 Jun 2013 23:37:45 -0400, Neel Rowhoiser said:
> > > I just stumbled across this and despite its sort of half-assed write
> up, I
> > > think its possibly an advisory? If I am understanding it correctly,
> they're
> > > saying that you can use a directory authority that hands out
> invalid/wrong RSA
> > > keys for other relays, you can cause decryption to fail and thus
> introduce path
> > > bias to nodes of the directory authorities choosing by selectively
> handing out
> > > valid RSA keys?
> >
> > Oh, it's *that* attack again (as far as I can tell).  Some French guys
> did a
> > proof-of-concept a few years ago that you could do this sort of thing if
> you
> > subverted a sufficient number of nodes.  But keep reading.
> >
> > > If the bit towards the end about guard nodes is correct, it would seem
> to
> > > indicate that they can use the semantics for detecting when a guard is
> causing
> > > too many extend relay cells to fail to cause valid guards to be marked
> invalid,
> > > and their rogue guards to succeed essentially using tor's semantics
> against
> > > them and causing the odds that you-re ingress point to the tor network
> is rogue
> > > to approach 1.
> >
> > The problem is that you have to subvert a large number of relays to
> > do it, in a way that doesn't get noticed..
> >
> > > Why aren't the tor relay keys signed? And what other myriad of
> documents do
> >
> > And who would sign said relay keys?  They're all essentially self-signed
> > already, so what you're looking for is a PKI.  And the whole point of
> the tor
> > system is that nobody involved trusts a central authority.  If you've
> got a
> > good idea on how to do it, feel free to comment.
> >
> > > directory authorities serve that also don't have integrity controls?
> This sort
> > > of makes me question the tor projects ability to deliver on any of the
> promises
> > > they make, as it would seem that a person needs like 3 or 4 rogue
> nodes before
> > > they could start de-anonymizing users, and the more of them they
> introduced the
> > > more of the network they could capture?
> >
> > Actually, it's more like 3 or 4 *hundred* nodes.  As I write this, there
> > are 3,903 relays connected, 1,218 guard nodes, and 2,396 directory
> mirrors.
> >
> > http://torstatus.blutmagie.de/
> >
> > Even if you control 400 of those routers, the odds that any connection
> will
> > only traverse your nodes is only 0.1% or so.  If you have "3 or 4', it's
> > literally a one-in-a-billion shot.  Assuming a million tor tunnels form a
> > day, you'd catch one circuit every 3 years or so.  And no guarantee that
> > the circuit you caught carried anything you would find useful.
> >
> > I suppose you could bring up 4,000 tor nodes of your own, to increase
> your odds
> > of end-to-end control on a circuit all the way to 12% or so. However,
> that's
> > very much a one trick pony, and probably wouldn't work simply because
> people
> > would notice the sudden growth before you got enough nodes connected to
> do much
> > damage.
> >
> > And using rogue directory servers to improve your odds doesn't help
> either.
> > Currently, there's a whole whopping 5 'bad exit' routers.  You can
> improve
> > your chances by corrupting stuff so half the exits are bad - but again,
> that
> > will get noticed when a single-digit number hits three digits.  And you
> need
> > to get it up to 4 digits before you have decent odds.
> >
> > And yes, the Tor designers are totally aware that this "vulnerability"
> > exists - the problem is that all proposed solutions so far are even
> > worse (for instance, requiring signed relay keys).
> >
>
>
>
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