Flaws in Tor anonymity network spotlighted

http://arstechnica.com/tech-policy/news/2010/12/flaws-in-tor-anonymity-network-spotlighted.ars

by kmfrk • 16 years ago

40 15 16 years ago

This exact same flaw exists for HTTPS. Well, SSL in general. It's not Tor specific.

jmillikin2• 16 years ago

HTTPS/TLS doesn't try to anonymize which site a client is accessing; any intermediate can read the address of outgoing packets to determine the server's identity. It's a little trickier when a server supports SNI, but few do.

TOR is supposed to prevent intermediaries from determining which sites a client is browsing, which is why this technique is interesting.

mike-cardwell5• 16 years ago

You can use this technique with Tor to make a reasonable guess if a user on your LAN is visiting a certain website.

You can also use this technique with plain https to see if a user that visits a certain website is downloading certain files from it, or accessing certain pages inside the website.

It is an interesting attack, but it's not one to get seriously worried about.

jmillikin2• 16 years ago

I'm doubtful of their 55-60% accuracy claim; how could a statistical analysis of encrypted traffic differentiate between samizdat and benign text? Or, more relevantly, whether someone browsing Wikipedia is looking up Tienanmen or just porn?

mike-cardwell5• 16 years ago

It's just simple traffic analysis. A page load generates a certain number of request/responses. Each request and response is a specific size, and will be transferred in a specific order. You create a fingerprint of that and it doesn't matter if the page is opened via a plain http channel, or https, or over Tor, The fingerprint will be the same (almost).

justsee• 16 years ago

But it's not that simple if the client is running as a relaying node as well, is it? The mixture of client traffic and relay traffic would make traffic analysis much more difficult.

Of course if you're that interesting that your ISP is doing traffic analysis on your connection you quite possibly have more pressing security issues.

aresant• 16 years ago

I don't get Tor - doens't the risk that somebody does something illicit that appers to originate from your IP render its value questionable?

EG the German arrested when a bomb threat was posted via Tor but traced back to his IP?

http://news.cnet.com/8301-13739_3-9779225-46.html

getsat3• 16 years ago

A handful of the highest throughput Tor exit nodes (named "blutmagie") are run by a single German fellow who is technically/legally his own ISP. Since it's not the same person, I'm assuming the one mentioned in the article did not go through all the same precautionary steps as the blutmagie admin.

http://anonymizer2.blutmagie.de/

bengross• 16 years ago

I wish the article's author had done a little bit of background work to find references to the CCC presenter's research.

Here is the paper published last year describing the research on fingerprinting. The second URL at uni-regensburg.de does not require an ACM account to download the paper.

Website fingerprinting: attacking popular privacy enhancing technologies with the multinomial naïve-bayes classifier http://portal.acm.org/citation.cfm?doid=1655008.1655013 http://epub.uni-regensburg.de/11919/1/authorsversion-ccsw09....

Dominik Herrmann, University of Regensburg, Regensburg, Germany Rolf Wendolsky, JonDos GmbH, Regensburg, Germany Hannes Federrath, University of Regensburg, Regensburg, Germany

"Privacy enhancing technologies like OpenSSL, OpenVPN or Tor establish an encrypted tunnel that enables users to hide content and addresses of requested websites from external observers This protection is endangered by local traffic analysis attacks that allow an external, passive attacker between the PET system and the user to uncover the identity of the requested sites. However, existing proposals for such attacks are not practicable yet.

We present a novel method that applies common text mining techniques to the normalised frequency distribution of observable IP packet sizes. Our classifier correctly identifies up to 97% of requests on a sample of 775 sites and over 300,000 real-world traffic dumps recorded over a two-month period. It outperforms previously known methods like Jaccard's classifier and Naïve Bayes that neglect packet frequencies altogether or rely on absolute frequency values, respectively. Our method is system-agnostic: it can be used against any PET without alteration. Closed-world results indicate that many popular single-hop and even multi-hop systems like Tor and JonDonym are vulnerable against this general fingerprinting attack. Furthermore, we discuss important real-world issues, namely false alarms and the influence of the browser cache on accuracy."

Also related (no account required to download the paper):

Compromising Tor Anonymity Exploiting P2P Information Leakage http://fr.arxiv.org/abs/1004.1461

Pere Manils, Chaabane Abdelberri, Stevens Le Blond, Mohamed Ali Kaafar, Claude Castelluccia, Arnaud Legout, Walid Dabbous (All - INRIA Sophia Antipolis / INRIA Rhône-Alpes)

"Privacy of users in P2P networks goes far beyond their current usage and is a fundamental requirement to the adoption of P2P protocols for legal usage. In a climate of cold war between these users and anti-piracy groups, more and more users are moving to anonymizing networks in an attempt to hide their identity. However, when not designed to protect users information, a P2P protocol would leak information that may compromise the identity of its users. In this paper, we first present three attacks targeting BitTorrent users on top of Tor that reveal their real IP addresses. In a second step, we analyze the Tor usage by BitTorrent users and compare it to its usage outside of Tor. Finally, we depict the risks induced by this de-anonymization and show that users' privacy violation goes beyond BitTorrent traffic and contaminates other protocols such as HTTP."

jondos• 16 years ago

Note that we at JonDonym will have developed a strong countermeasure within the next few weeks...

Flaws in Tor anonymity network spotlighted

Related Stories