On the Effectiveness of Traffic Analysis Against Tor Networks Using Flow Records [pdf]
mice.cs.columbia.edu
mice.cs.columbia.edu
It relies on a malicious server and entry node. The contribution of this paper is that if you have the malicious server and entry node, you can use a less expensive data source (Cisco NetFlow data) rather than raw packets to perform a correlation attack.
The correlation they achieve in a private Tor network is impressive; however, if you look at the graphs in the actual paper[0], you can see that the differences in correlations are actually quite small in the wild.
The title of this post and article is actually incorrect; the technique demonstrated has an 81.4% accuracy. This means that the base rate fallacy will make it nearly unusable in practice, and more so as the scale of Tor traffic grows. For more on the Base Rate Fallacy, see [1].
So in summary:
* This is an incremental improvement of an already existing and known attack pattern on low-latency anonymity systems
* The technique presented in this paper is only a threat if your threat model is an adversary that can control your entry guard and the server you are trying to communicate with, but does not have the budget for packet-level correlation attacks
* This technique does not achieve sufficiently high accuracy and sufficiently low false positives to reliably identify arbitrary Tor users, but might be more successful if used in combination with a prior hypothesis that, say, a specific NSA employee is communicating with GlobalLeaks.
[0] https://mice.cs.columbia.edu/getTechreport.php?techreportID=...
To put it another way, let's say someone is posting bomb threats over Tor on Google Plus. Google cooperates with the FBI and deterministically perturbs all traffic going into the Tor network. What router does the FBI get netflow data from in order to find the bomber?
I know that it does not do this, but couldn't it ?
You can thank DDOS trolls for that, I guess, because that's why the ISPs paid to build that out.
If tier 1 ISP differentiate traffic on port level, then switching that setting on should bypass the filter.
Hiding in port 80 will protect you not-at-all from traffic analysis, and all the major ISPs already have the infrastructure to deploy traffic analysis.
http://en.wikipedia.org/wiki/Freenet
Upsides: Much more secure than Tor, (since it doesn't try to be a low-latency mixing router) not funded by USG.
Downsides: Real slow. Real slow. SLOW. Think effective throughput in the tens of kilobytes/s, latency measured in minutes.
Phantom also seems to have great design, but it was discontinued quite early in its implementation. No idea if it's because it was unworkable or for other reasons. Maybe someone with experience in such networks can take a look at it:
However Tor has a big advantage in practice right now: lots of users, of every kind, to hide among.
When GCHQ talked about "staining" in this context (as in the REMATION conference docs), by the way, they generally mean either a timing-based fingerprint (as here) or cookie-based fingerprint (unfortunately it seems to be used in at least two entirely different contexts, oh well).
Big security downside is that in the purely opennet configuration, your peer nodes are both untrusted strangers AND your own traffic is visible to them. There is NO "onion" effect going on, just reliance on the possibility that any traffic a peer node observes from your node is not necessarily YOUR traffic as all nodes are also routing requests for other nodes.
Most academic computer science is funded by the American government. Does that mean that all academic computer science is backdoored by the military?
To put it more specifically, most compilers researchers I know have at some point been on a DARPA grant, because DARPA has money and academics want money. I'm sure plenty of LLVM contributors have been paid from DARPA grants. Is LLVM backdoored?
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On an entirely different point, how is Freenet even comparable to Tor? They address totally different use cases (Tor is an anonymizing TCP overlay; Freenet is a distributed censorship-resistant store), and have very different threat models.
Further, it seems very unlikely that Tor (which is a piece of very well-maintained software with some of the foremost privacy researchers working on it) would have fewer bugs than Freenet, which is a sprawling Java program maintained by one man. Further, the security of Freenet in abstract hugely depends on having a functional small-world network, which requires Freenet to have been widely adopted to start with.
The comment parent's request was vague, but you simply cannot replace Tor with Freenet because they do totally different things. It is nonsensical to compare them because they address different threat models and accomplish different goals.
For example, people use both Tor and Freenet to enable anonymized private messaging. On Tor, this is achieved by connecting to a hidden-service forum and posting. On Freenet, this is achieved through an app that uses Shared Subspace Keying to basically have two people watch one-another's RSS feeds for updates. Either way, people get to send anonymous messages and have other anonymous people see them.
I always like to remind people that Tor is funded by the USG (currently, actively). I think it's very important that people understand that and adjust their threat models based on that.
However, it's not all bad news ... in fact, I think there's a very significant upside to the USG funding of Tor:
It provides a very compelling defense in the event that simply participating in Tor begins to be prosecuted.
There is very often a worry put forth that simply participating in Tor (as a client or by running a relay, etc.) can in itself be considered an illegal act. I think that as long as the USG is funding the development, people in the US can rest easy that they can't be prosecuted in any way for simply participating on the Tor network.
"If the USG is funding it and the state department is encouraging people to use it (think arab spring) then how could my use of it be illegal ?"
IANAL.
Also, the Tor Project periodically sends out folks to remind the FBI and friends that tor has many legitimate uses, and is routinely used by law enforcement agencies as part of their day-to-day business. [1]
[0] https://lists.torproject.org/pipermail/tor-talk/2011-March/0...
[1] https://blog.torproject.org/blog/trip-report-october-fbi-con...
If you were some one who believed that your liberty or even life depended on it, then yes, you would have to assume that. Obviously day to day, it really doesn't matter. When it actually does matter, you have to assume the worst.
Here's my blog key if you want to try:
USK@1ORdIvjL2H1bZblJcP8hu2LjjKtVB-rVzp8mLty~5N4,8hL85otZBbq0geDsSKkBK4sKESL2SrNVecFZz9NxGVQ,AQACAAE/bluishcoder/3/
USK@2LK9z-pdZ9kWQfw~GfF-CXKC7yWQxeKvNf9kAXOumU4,1eA8o~L~-mIo9Hk7ZK9B53UKY5Vuki6p4I4lqMQPxyw,AQACAAE/pitcairnisland/0/Instead your node is no more statistically likely to have any portion of the objects you've uploaded than any other objects throughout Freenet. When an upload is complete your node doesn't have a full copy, all the chunks are spread out amongst the nodes within a few hops of you instead.
When it's developed entirely in the open I'm not sure I see the concern here. If you have reason to believe they are somehow compromised or backdooring Tor please do share it, otherwise this is just FUD.
Seems like a lot of security products demand trust from their users (even gnunet). This implicit bossing is no less pretentious than a gas pump that says "Thankyou".
You give up a certain amount of security, but gain a lot of comfort.
Perhaps a future version of tor can offer a "comfort level" setting that introduces a varying amount of delays, bogus traffic and other concealment methods (ideally at every hop).
He who sacrifices security for comfort deserves neither :)
How well does Tor do with panopticlick?
Update: Tor Browser in Tails 1.2 with javascript disabled returns a fingerprint that's shared by 1 in 2,615 with 11.35 bits of identifying information.
>Within our dataset of several million visitors, only one in 4,955 browsers have the same fingerprint as yours.
>Currently, we estimate that your browser has a fingerprint that conveys 12.27 bits of identifying information.
I figured it would be more unique due to my running Tor Browser on a Mac - but I don't see how the math works out. Unless it actually has a count of machines with information identical to mine?
How else would it work (not assuming even distribution)? Im sure its a hash counter.
If your fingerprint is totally unique (like mine, with 22.16 bits of information) then it is shared by only 1 in 4,697,672 browsers in their dataset.
That said, browser fingerprinting is very hard to fight, and it's a lot easier to come up with new fingerprinting techniques than it is to mitigate them. So I expect that determined fingerprinters have the edge in this arms race.
Currently, we estimate that your browser has a fingerprint that conveys at least 22.16 bits of identifying information.
Well, shit. I'm a snowflake.
Also, Panopticlick hasn't been updated with some possible distinguishing measurements that have been identified since it was created. In that sense it was always meant as a lower bound on uniqueness, and should still be understood that way.
There are lots of downsides to this (epistemic attacks), but if your anon use case makes sense for such a setup, it is a valuable tool to have in the toolbox.
If you just config it with PublishServerDescriptor as 0 and someone else knows the IP (middle relays) they will be able to use it.
It's essentially a function of not announcing the node to anyone.
Edit: And to be clear, priv exit nodes don't prevent the timing attack in the article.
As for paying for services such that "customer of this VPN provider" can't be linked to you, I'd look at places that specifically accept bitcoin (I'm not a fan in general, but in this case, it signals their willingness to avoid collecting normal billing data like name, address, cc#, etc.).
I have no affiliation but they popped up in the googlings. Seems to be simple enough to get their service without giving away anything personally identifiable.
EDIT: the reason I tease out those two parts is because I'm concerned people will think TOR can protect against entities that can do a global customer-of-VPN dereference. TOR doesn't protect against global super-adversaries, consult your local security practitioner before feeling safe, etc. etc.
At the moment if I start up my VPN client and wait for the connection to my very trustworthy VPN provider, and only then open to Tor Browser Bundle, is that the right way round?
Thanks for the clarification.
TorrentFreak did a really good comparison of them recently: http://torrentfreak.com/which-vpn-services-take-your-anonymi...
Second, "no logs"... well: https://www.bestvpn.com/blog/8383/earthvpn-user-arrested-cop...
Good luck with your "no logs" operation in any NATO member/friendly country. Not sure about Russia and its allies, but I expect you'd be hard pressed to achieve "no logs" in China as well. South-Africa and Israel is probably out too. Not sure what that leaves you.
Of course, the issue is that latency in this scheme is O(n) and per-node bandwidth is O(1/n), with large constants. Also, it's a reasonable suspicion in practice that no one would set up this scheme and then actually have zero communication going on over it, so it still reveals that "at least one of the n nodes is talking to at least another of the n nodes".
I may be paranoid, but it seems to be that there is some FUD around tor lately. And if many people will stop using it, it will indeed become less secure.
HN should uphold a higher standard than that. Link to the source.
That said, papers in computing are an exception because the audience here is informed in that field. And the thread, at this point, provides a lot of context.
Given the above I think the paper is probably the better URL, and we've changed to it from http://thestack.com/chakravarty-tor-traffic-analysis-141114.
Marking this subthread as obviously off-topic.