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I am a post-doctoral visiting fellow at the Cosic group (Privacy group), ESAT, K.U.Leuven, in Flanders, Belgium. I am funded by the FWO (Flamish research council) to work on privacy, anonymity and traffic analysis. My boss here is Bart Preneel.
Previously I have been a research assistant in the Security Group,
of the Computer Laboratory of
the University of Cambridge,
working on anonymous communications, peer-to-peer networks and
censorship resistance. I also got my Ph.D, M.A. and B.A at the Cambridge University, Computer Laboratory under the supervision of Prof. Ross Anderson.
Latest news
I am experimenting with the google custom search engines for computer security. You can contribute if you like!
Mike Bond and I just published a new technical report entitled "A pact with the Devil" (see Techical Report 666). We look at how viruses may give benefits to the owners of the computers they propagate on in conjunction to using threats and blackmail to entrench themselves.
New work on the Economics of mass surveillance and the (questionable) value of anonymous communications is available. We look at target selection strategies for maximizing surveillance (or disruption) return based on data collected from a real social network. It turns out that current anonymous communications solutions do not pretoect too well against such target selection. Our data sets and scripts will soon be made available...
During my CST Part II Project I have done an experimental implementation of Mixes and Dining cryptographers networks. The code is available here (tar.gz)(The whole thing is highly experimental and one should be mad to use it for anything important). The project report explaining the implementation issues is available (pdf). As a result of this work I gave a talk in the Cambridge Protocols Workshop 2000 on Money Escrow, a method to combat dead-beat biders in auction protocols. A revised version of the slides used in this talk is available (pdf,ps).
I have been working with Richard and Markus assesing real life systems that provide Anonymous services. We document real patterns of failure in these systems, and work towards a security model for pseudonymity (pdf,html).
Some people have been sending me anonymous emails without including a reply block, therefore not giving me the ability to answer their questions. For this reason I have built a new page with replies to anonymous emails. Make sure you access it using a suitable anonymizing proxy!
Anonymous communications:
What can you do with traffic analysis? Often people ask me the same
question so I have a presentation
and a
background paper introducing the topic. They were both prepared for my talk at the Santa's Crypto Get-together in Prague, December 2005.
In order to better evaluate anonymous systems and attacks against the anonymity properties of systems,
Andrei Serjantov
and I, propose a new definition of the "Anonymity set". We move away from the classic world of set theory toward a definition that takes into account probability distributions over different participants and redefine anonymity sets using entropy and other tools borrowed from information theory. This metric allows a better qualitative understanding of anonymity and allows researchers to move beyond the typical all-or-nothing approach to these systems and their failures. The paper that describes these definitions is available in
ps
and
pdf format. It
appeared at PET2002, and got an
award at PET2003.
Lately I have been working on traffic Analysis, and a preliminary poster of some results appeared at the "Workshop on Privacy and Identity in the Information Society: Systemic Risks" (5-6th February 2002).
Along with others, we are collaborating to design and build MixMinion, the next generation of anonymous remailers. They should support sender-receiver anonymous communications, and support for forward security on the links. The development lists are public, and the first design document is also available.
In order to strengthen mixes against new legal attack, such as compulsion to reveal keys, I have proposed the design of forward secure mixes. Using key updating techniques, even the intermediate nodes that have in the past processed the message cannot trace it back, provided they follow the protocols. A paper presenting these ideas has been presented at the NorSec2002 conference.
I have spent some time exploring the use of javascript as a way to implement cryptographic algorithms. A system implementing ElGamal encryption can be found here.
We have been implementing with Richard "Chaffinch", a system that provides confidentiality and plausible deniability using only authentication primitives. The paper destibing it in detail can be found here [pdf,html]. The Chaffinch system has its own web page.
Policy issues:
Some original sources relating the technical details of the
latest Greek interception scandals were translated into English.
In December 2001 I took part in the EU Cybercrime forum on the subject of the retention of traffic data, as part of the Internet Rights Europe initiative. My positions on the subject, and the other contributions, can be found here. Other sources of information about data retention are EPIC, FIPR, Statewatch
My position on the issue of traffic data retention and its impact on
civil society was presented at the first World Civil Society Forum, in
Geneva. The position paper
and the slides
are available.
George Danezis, Stephen Lewis and Ross Anderson. How Much is Location Privacy Worth?. Fourth Workshop on the Economics of Information Security (WEIS 2005). Harvard University, 2 - 3 June 2005.
Steven J. Murdoch and George Danezis. Low-cost Traffic Analysis of Tor. 2005 IEEE Symposium on Security and Privacy, May 8-11, 2005, Oakland, California, USA.
The social network analysis framework
used
for "The Economics of
Surveillance" research. Python code including a map apply core,
libraries for network ploting and KD-Trees, and all the data.
Teaching
A few part II project proposals/MSc/Erasmus that I would like to supervise can be
found at here. If
you are interested in a project related to anonymity feel free to
contact me.
I also gave a lecture
on anonymity for the Cambridge Part II computer security course.