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

Joe Btfsplk joebtfsplk at gmx.com
Sat Feb 25 20:49:19 UTC 2012

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.
> 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 
If an ISP sets up an entry relay or bridge & exit relay, you could be 
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/ 

More information about the tor-talk mailing list