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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