Re: [tor-talk] on the topic of tor's weaknesses

[Chris Wheeler <grintor@xxxxxxxxx>]

Joe, I don't think that the order that the packet are sent
and received from the exit relay really changes the ease of correlation,
since they will arrive to the other end of the network in the same order.
But maybe the middle relay could be the one who re-arranges the packets.
Delaying some and expediting others randomly. TCP handles out of order
packets badly by my understanding, it just requests them again in the
correct order. There would need to be a protocol wrapped around the TCP
stream being proxied that puts them back in order at the exit and entrance
relays transparent to the TCP stream. Sounds possible to me. But you know,
even if you didn't rearrange them and just randomly delayed each packet
(but kept them in order) at each hop it seems that would make
it impossible to correlate. Unless maybe if there were only one stream
passing through a node at a given time (which is pretty likely to happen on
new bridges). To solve that problem you could have each node always sending
and receiving by just sending "junk" packets (whole packets of padding)
around the network. Once they hit an exit node the exit would decrypt them,
see they were just padding and toss them out. That would create more
overhead but might be worth it.

On Sat, Feb 25, 2012 at 3:49 PM, Joe Btfsplk <joebtfsplk@xxxxxxx> wrote:

> On 2/25/2012 12:41 PM, Xinwen Fu wrote:
>
>> Chris,
>>
>> An attack may only work under its own threat model (capabilities and
>> resources an adversary has). If entries and exit are all secure, some
>> correlation attacks may not work. However, if the adversary can still
>> observe (not need to compromise Tor routers) the traffic into and out of
>> entries and exits, some attacks may still work, e.g., by correlating the
>> traffic patterns at the two sides of a circuit. Here is a paper describing
>> such possibility:
>> http://www.cs.uml.edu/~**xinwenfu/paper/TorCellSize_**ICC11_Fu.pdf<http://www.cs.uml.edu/~xinwenfu/paper/TorCellSize_ICC11_Fu.pdf>
>> .
>>
>> Hope it helps a bit.
>>
>> Xinwen Fu
>>
> Thanks for the link, Xinwen.  I have a more basic question regarding the
> original question of adversaries somehow getting access to BOTH entry &
> exit nodes, that lots of users probably are curious about.  Re:  getting
> enough data (even if they could break encryption, if using * SSL *) to do
> any good.  Since Tor / Vidalia changes nodes often (is it at least every 10
> min, at most? - & more often if a circuit fails), could an adversary get
> enough data about ONE user to do any good?
>
> In this case, is the threat that the adversary will ONLY be able to
> identify that one is USING Tor network (not capture the actual data
> transferred), assuming they have access to the * originating IP address,*
> going to the entry node AND also to the exit node?  I suppose (for now),
> adversaries in repressive countries determining that one is USING Tor is a
> big problem.  Not so much in "free" societies, but that could change.
>
> What effect, if any, would Tor changing relays more frequently than the
> current default time, have on ability of adversaries tracking users (in a
> meaningful manner) from entry to exit nodes?
>
> In Tor network, does the data packet size & order, in & out of entry or
> exit nodes necessarily HAVE to be the same?  Would it be possible to make
> the  in & out packet sizes different sizes, or mix the order of packets at
> an exit vs entry node?  (I don't know the technicality of how this would
> work).  If you d/l a torrent (as an example), you don't receive the file
> pieces in order.  Is it theoretically possible  the Tor network could
> develop a way to mix up the packets (of a file), within the network, so
> that even if an adversary had complete access to a given entry & exit
> node(s), the data going in one end could never be matched w/ data coming
> out?  (don't answer too quickly!  Never say never)
>
> This is also somewhat similar in concept to the old data correction
> process, where pieces of a file might be re transferred (due to
> corruption), much later in the d/l process, after most of the file was
> already downloaded.
>
> The theoretical concept I'm pondering is, could all pieces of data
> transmission through Tor be scrambled (the order and / or size) on purpose?
>  Adversaries generally can't read the actual data because of encryption (if
> I understand).  If there was also no correlation of packets (to an outside
> observer) at one end vs the other, how could they ever track a user by
> traffic analysis?  Adversaries would theoretically have to monitor ALL
> relays, ALL of the time.
>
> Even then, how would they track a user, end to end, if the packet order is
> purposefully & randomly jumbled within the network?  It seems that the
> current Tor network model will come under ever increasing attacks /
> monitoring & needs to change the fundamental way it operates.
>
> To some avg users, it might seem there is no way around a determined
> adversary determining they are using Tor (with current Tor network
> technology).
> If an ISP sets up an entry relay or bridge & exit relay, you could be
> screwed.
> If a user goes through a proxy to Tor, and an adversary runs the proxy
> (how do we really know?), you could be screwed.
>
> I could go on & on w/ scenarios.  Lots of people throw around the phrase,
> "Users have to determine their threat model..."  Quite honestly, most
> people wouldn't know how.  For avg users, advanced users may as well say,
> "We have no idea.  You're own your own.  Don't assume you'll be anonymous,
> even if you follow directions exactly for using Tor / TBB."
>
> OK, so instead of everyone shooting down my ideas, modify them so they
> might work, or come up w/ other better ideas, instead of continuing to put
> band aids on the current technology that seems to be fraught w/ problems.
>
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