Learn, hack!

Hacking and security documentation: slides, papers, video and audio recordings. All in high-quality, daily updated, avoiding security crap documents. Spreading hacking knowledge, for free, enjoy. Follow on .

Taking control over the Tor network

Eric Filiol, Seun Omosowon
Chaos Communication Congress 28th (28C3) 2011
Indexed on
Mar 27, 2013
File name
File size
524.8 MB

This talk deals with weaknesses identified in the TOR network protocol and cryptography implementation. We manage to take control over users using this network and to access all your information and data exchanged despite cryptography. The TOR network is one of the most famous way to use Internet in a anonymous and secure way at least supposedly. Tor client software routes Internet traffic through a worldwide volunteer network of servers in order to conceal a user's location or usage from someone conducting network surveillance or traffic analysis. Aside protocol-oriented aspects, TOR security relies heavily on cryptography. The aim of this talk is to explain how it is possible to take over a significant part of the TOR network not to say over the whole network. We have identified two classes of weaknesses in the way Onion routers (Ors) are managed: a first class of weaknesses relates to the way the routes among Ors. It is possible to influence and to force users to use arbitrary Ors and hence control which route they take. A second class of weaknesses relates to the way cryptography is implemented. Bu using malware-based attacks and the concept of dynamic cryptographic backdoors we have succeeded to circumvent the cryptography in place without removing it. We present different possible attack scenarii which are malware-based or not (depending on the scenario considered) that have been experimented and validated on a TOR simulation network of 50 nodes and partially on the real TOR network (as far as it was possible regarding existing laws). We show that it is indeed possible to gain a lot of sensitive information thus bypassing and managing existing cryptographic mechanisms in a very efficient way and to take the effective control over a significant part of the TOR network. The attack is fully dynamic and can be replayed on request. We present an open source library that enable to automate the identification of hidden relay bridges. We propose some modification in the TOR source and protocol in order to prevent those attacks. Demos will be presented to expose the two class of vulnerabilities we exploit. An Internet access is required to make part of the demos on the real TOR network.

About us

Secdocs is a project aimed to index high-quality IT security and hacking documents. These are fetched from multiple data sources: events, conferences and generally from interwebs.


Serving 8166 documents and 531.0 GB of hacking knowledge, indexed from 2419 authors from 163 security conferences.


To support this site and keep it alive, you can click on the buttons below. Any help is really appreciated! This service is provided for free, but real money is needed to pay bills.

Flattr this Click here to lend your support to: Keep live SecDocs for an year and make a donation at www.pledgie.com !