Category Archives: Privacy technology

Anonymous communication, data protection

EFF and Tor Project in Google Summer of Code

Internet censorship, Privacy technology

The EFF and the Tor Project have been accepted into Google Summer of Code. This programme offers students a stipend for contributing to open source software over a 3 month period. Google Summer of Code has been running since 2005 and the Tor project has been a participant since 2007.

We are looking for talented and motivated students to work on a number of projects to improve Tor, and related applications. Students are also welcome to come up with their own ideas. Applications must be submitted by 3 April 2009. For further information, and details on how to apply, see the Tor blog.

Hot Topics in Privacy Enhancing Technologies (HotPETs 2009)

Academic papers, Call for papers, Privacy technology

HotPETs – the 2nd Hot Topics in Privacy Enhancing Technologies (co-located with PETS) will be held in Seattle, 5–7 August 2009.

HotPETs is the forum for new ideas on privacy, anonymity, censorship resistance, and related topics. Work-in-progress is welcomed, and the format of the workshop will be to encourage feedback and discussion. Submissions are especially encouraged on the human side of privacy: what do people believe about privacy? How does privacy work in existing institutions?

Papers (up to 15 pages) are due by 8 May 2009. Further information can be found in the call for papers.

Forensic genomics

Academic papers, Legal issues, Politics, Privacy technology

I recently presented a paper on Forensic genomics: kin privacy, driftnets and other open questions (co-authored with Lucia Bianchi, Pietro Liò and Douwe Korff) at WPES 2008, the Workshop for Privacy in the Electronic Society of ACM CCS, the ACM Computer and Communication Security conference. Pietro and I also gave a related talk here at the Computer Laboratory in Cambridge.

While genetics is concerned with the observation of specific sections of DNA, genomics is about studying the entire genome of an organism, something that has only become practically possible in recent years. In forensic genetics, which is the technology behind the large national DNA databases being built in several countries including notably UK and USA (Wallace’s outstanding article lucidly exposes many significant issues), investigators compare scene-of-crime samples with database samples by checking if they match, but only on a very small number of specific locations in the genome (e.g. 13 locations according to the CODIS rules). In our paper we explore what might change when forensic analysis moves from genetics to genomics over the next few decades. This is a problem that can only be meaningfully approached from a multi-disciplinary viewpoint and indeed our combined backgrounds cover computer security, bioinformatics and law.

CODIS markers
(Image from Wikimedia commons, in turn from NIST.)

Sequencing the first human genome (2003) cost 2.7 billion dollars and took 13 years. The US’s National Human Genome Research Institute has offered over 20 M$ worth of grants towards the goal of driving the cost of whole-genome sequencing down to a thousand dollars. This will enable personalized genomic medicine (e.g. predicting genetic risk of contracting specific diseases) but will also open up a number of ethical and privacy-related problems. Eugenetic abortions, genomic pre-screening as precondition for healthcare (or even just dating…), (mis)use of genomic data for purposes other than that for which it was collected and so forth. In various jurisdictions there exists legislation (such as the recent GINA in the US) that attempts to protect citizens from some of the possible abuses; but how strongly is it enforced? And is it enough? In the forensic context, is the DNA analysis procedure as infallible as we are led to believe? There are many subtleties associated with the interpretation of statistical results; when even professional statisticians disagree, how are the poor jurors expected to reach a fair verdict? Another subtle issue is kin privacy: if the scene-of-crime sample, compared with everyone in the database, partially matches Alice, this may be used as a hint to investigate all her relatives, who aren’t even in the database; indeed, some 1980s murders were recently solved in this way. “This raises compelling policy questions about the balance between collective security and individual privacy” [Bieber, Brenner, Lazer, 2006]. Should a democracy allow such a “driftnet” approach of suspecting and investigating all the innocents in order to catch the guilty?

This is a paper of questions rather than one of solutions. We believe an informed public debate is needed before the expected transition from genetics to genomics takes place. We want to stimulate discussion and therefore we invite you to read the paper, make up your mind and support what you believe are the right answers.

Liberal Democrat leader visits our lab

Banking security, News coverage, Politics, Privacy technology

This week, Nick Clegg, leader of the UK Liberal Democrat Party, and David Howarth, MP for Cambridgeshire, visited our hardware security lab for a demonstration of Chip & PIN fraud techniques.

They used this visit to announce their new party policy on protections against identity fraud. At present, credit rating companies are exempt from aspects of the Data Protection Act and can forward personal information about an individual’s financial history to companies without the subject’s consent. Clegg proposes to give individuals the rights to “freeze” their credit records, making it more difficult for fraudsters to impersonate others.

See also the Cambridge Evening News article and video interview.

Privacy Enhancing Technologies Symposium (PETS 2009)

Academic papers, Call for papers, Privacy technology

I am on the program committee for the 9th Privacy Enhancing Technologies Symposium (PETS 2009), to be held in Seattle, WA, USA, 5–7 August 2009. PETS is the leading venue for research on privacy and anonymity, offering an enjoyable environment and stimulating discussion. If you are working in this field, I can strongly recommend submitting a paper.

This year, we are particularly looking for submissions from topics other than anonymous communications, so if work from your field may be applied, or is otherwise related, to the topic of privacy, I’d encourage you to consider PETS as a potential venue.

The submission deadline for the main session is 2 March 2009. As with last year, we will also have a “HotPETS” event, for new and exciting work in the field which is still in a formative state. Submissions for HotPETS should be received by 8 May 2009.

Further information can be found in the call for papers.

PET Award 2008

Academic papers, Awards, Privacy technology

At last year’s Privacy Enhancing Technologies Symposium (PETS), I presented the paper “Sampled Traffic Analysis by Internet-Exchange-Level Adversaries”, co-authored with Piotr Zieliński. In it, we discussed the risk of traffic-analysis at Internet exchanges (IXes). We then showed that given even a small fraction of the data passing through an IX it was still possible to track a substantial proportion of anonymous communications. Our results are summarized in a previous blog post and full details are in the paper.

Our paper has now been announced as a runner-up for the Privacy Enhancing Technologies Award. The prize is presented annually, for research which makes an outstanding contribution to the field. Microsoft, the sponsor of the award, have further details and summaries of the papers in their press release.

Congratulations to the winners, Arvind Narayanan and Vitaly Shmatikov, for “Robust De-Anonymization of Large Sparse Datasets”; and the other runner-ups, Mira Belenkiy, Melissa Chase, C. Chris Erway, John Jannotti, Alptekin Küpçü, Anna Lysyanskaya and Erich Rachlin, for “Making P2P Accountable without Losing Privacy”.

Finland privacy judgment

Legal issues, News coverage, Politics, Privacy technology, Security engineering

In a case that will have profound implications, the European Court of Human Rights has issued a judgment against Finland in a medical privacy case.

The complainant was a nurse at a Finnish hospital, and also HIV-positive. Word of her condition spread among colleagues, and her contract was not renewed. The hospital’s access controls were not sufficient to prevent colleages accessing her record, and its audit trail was not sufficient to determine who had compromised her privacy. The court’s view was that health care staff who are not involved in the care of a patient must be unable to access that patient’s electronic medical record: “What is required in this connection is practical and effective protection to exclude any possibility of unauthorised access occurring in the first place.” (Press coverage here.)

A “practical and effective” protection test in European law will bind engineering, law and policy much more tightly together. And it will have wide consequences. Privacy compaigners, for example, can now argue strongly that the NHS Care Records service is illegal. And what will be the further consequences for the Transformational Government initiative – the “Database State”?

Metrics for security and performance in low-latency anonymity systems

Academic papers, Privacy technology, Security engineering

In Tor, and in other similar anonymity systems, clients choose a random sequence of computers (nodes) to route their connections through. The intention is that, unless someone is watching the whole network at the same time, the tracks of each user’s communication will become hidden amongst that of others. Exactly how a client chooses nodes varies between system to system, and is important for security.

If someone is simultaneously watching a user’s traffic as it enters and leaves the network, it is possible to de-anonymise the communication. As anyone can contribute nodes, this could occur if the first and last node for a connection is controlled by the same person. Tor takes some steps to avoid this possibility e.g. no two computers on the same /16 network may be chosen for each connection. However, someone with access to several networks could circumvent this measure.

Not only is route selection critical for security, but it’s also a significant performance factor. Tor nodes vary dramatically in their capacity, mainly due to their network connections. If all nodes were chosen with equal likelihood, the slower ones would cripple the network. This is why Tor weights the selection probability for a node proportional to its contribution to the network bandwidth.

Because of the dual importance of route selection, there are a number of proposals which offer an alternative to Tor’s bandwidth-weighted algorithm. Later this week at PETS I’ll be presenting my paper, co-authored with Robert N.M. Watson, “Metrics for security and performance in low-latency anonymity systems”. In this paper, we examine several route selection algorithms and evaluate their security and performance.

Intuitively, a route selection algorithm which weights all nodes equally appears the most secure because an attacker can’t make their node count any more than the others. This has been formalized by two measures: Gini coefficient and entropy. In fact the reality is more complex — uniform node selection resists attackers with lots of bandwidth, whereas bandwidth-weighting is better against attackers with lots of nodes (e.g. botnets).

Our paper explores the probability of path compromise of different route selection algorithms, when under attack by a range of different adversaries. We find that none of the proposals are optimal against all adversaries, and so summarizing effective security in terms of a single figure is not feasible. We also model the performance of the schemes and show that bandwidth-weighting offers both low latency and high resistance to attack by bandwidth-constrained adversaries.

Update (2008-07-25):
The slides (PDF 2.1M) for my presentation are now online.

Security psychology

Politics, Privacy technology, Security economics, Security engineering

I’m currently in the first Workshop on security and human behaviour; at MIT, which brings together security engineers, psychologists and others interested in topics ranging from deception through usability to fearmongering. Here’s the agenda and here are the workshop papers.

The first session, on deception, was fascinating. It emphasised the huge range of problems, from detecting deception in interpersonal contexts such as interrogation through the effects of context and misdirection to how we might provide better trust signals to computer users.

Over the past seven years, security economics has gone from nothing to a thriving research field with over 100 active researchers. Over the next seven I believe that security psychology should do at least as well. I hope I’ll find enough odd minutes to live blog this first workshop as it happens!

[Edited to add:] See comments for live blog posts on the sessions; Bruce Schneier is also blogging this event.

An improved clock-skew measurement technique for revealing hidden services

Academic papers, Hardware & signals, Privacy technology

In 2006 I published a paper on remotely estimating a computer’s temperature, based on clock skew. I showed that by inducing load on a Tor hidden service, an attacker could cause measurable changes in clock skew and so allow the computer hosting the service to be re-identified. However, it takes a very long time (hours to days) to obtain a sufficiently accurate clock-skew estimate, even taking a sample every few seconds. If measurements are less granular than the 1 kHz TCP timestamp clock source I used, then it would take longer still.

This limits the attack since in many cases TCP timestamps may be unavailable. In particular, Tor hidden services operate at the TCP layer, stripping all TCP and IP headers. If an attacker wants to estimate clock skew over the hidden service channel, the only directly available clock source may be the 1 Hz HTTP timestamp. The quantization noise in this case is three orders of magnitude above the TCP timestamp case, making the approach I used in the paper effectively infeasible.

While visiting Cambridge in summer 2007, Sebastian Zander developed an improved clock skew measurement technique which would dramatically reduce the noise of clock-skew measurements from low-frequency clocks. The basic idea, shown below, is to only request timestamps very close to a clock transition, where the quantization noise is lowest. This requires the attacker to firstly lock-on to the phase of the clock, then keep tracking it even when measurements are distorted by network jitter.

Synchronized vs random sampling

Sebastian and I wrote a paper — An Improved Clock-skew Measurement Technique for Revealing Hidden Services — describing this technique, and showing results from testing it on a Tor hidden service installed on PlanetLab. The measurements show a large improvement over the original paper, with two orders of magnitude lower noise for low-frequency clocks (like the HTTP case). This approach will allow previous attacks to be executed faster, and make previously infeasible attacks possible.

The paper will be presented at the USENIX Security Symposium, San Jose, CA, US, 28 July – 1 August 2008.