Tor at the Heart: PETS and the Privacy Research Community

During the month of December, we're highlighting other organizations and projects that rely on Tor, build on Tor, or are accomplishing their missions better because Tor exists. Check out our blog each day to learn about our fellow travelers. And please support the Tor Project! We're at the heart of Internet freedom. Donate today!

So far in this blog series we've highlighted mainly software and advocacy projects. Today is a little different: I'm going to explain more about Tor's role in the academic world of privacy and security research.

Part one: Tor matters to the research community

Just about every major security conference these days has a paper analyzing, attacking, or improving Tor. While ten years ago the field of anonymous communications was mostly theoretical, with researchers speculating that a given design should or shouldn't work, Tor now provides an actual deployed testbed. Tor has become the gold standard for anonymous communications research for three main reasons:

First, Tor's source code and specifications are open. Beyond its original design document, Tor provides a clear and published set of RFC-style specifications describing exactly how it is built, why we made each design decision, and what security properties it aims to offer. The Tor developers conduct design discussion in the open, on public development mailing lists, and the public development proposal process provides a clear path by which other researchers can participate.

Second, Tor provides open APIs and maintains a set of tools to help researchers and developers interact with the Tor software. The Tor software's "control port" lets controller programs view and change configuration and status information, as well as influence path selection. We provide easy instructions for setting up separate private Tor networks for testing. This modularity makes Tor more accessible to researchers because they can run their own experiments using Tor without needing to modify the Tor program itself.

Third, real users rely on Tor. Every day hundreds of thousands of people connect to the Tor network and depend on it for a broad variety of security goals. In addition to its emphasis on research and design, The Tor Project has developed a reputation as a non-profit that fosters this community and puts its users first. This real-world relevance motivates researchers to help make sure Tor provides provably good security properties.

I wrote the above paragraphs in 2009 for our first National Science Foundation proposal, and they've become even more true over time. A fourth reason has also emerged: Tor attracts researchers precisely because it brings in so many problems that are at the intersection of "hard to solve" and "matter deeply to the world". How to protect communications metadata is one of the key open research questions of the century, and nobody has all the answers. Our best chance at solving it is for researchers and developers all around the world to team up and all work in the open to build on each other's progress.

Since starting Tor, I've done probably 100 Tor talks to university research groups all around the world, teaching grad students about these open research problems in the areas of censorship circumvention (which led to the explosion of pluggable transport ideas), privacy-preserving measurement, traffic analysis resistance, scalability and performance, and more.

The result of that effort, and of Tor's success in general, is a flood of research papers, plus a dozen research labs who regularly have students who write their thesis on Tor. The original Tor design paper from 2004 now has over 3200 citations, and in 2014 Usenix picked that paper out of all the security papers in 2004 to win their Test of Time award.

Part two: University collaborations

This advocacy and education work has also led to a variety of ongoing collaborations funded by the National Science Foundation, including with Nick Feamster's group at Princeton on measuring censorship, with Nick Hopper's group at University of Minnesota on privacy-preserving measurement, with Micah Sherr's group at Georgetown University on scalability and security against denial of service attacks, and an upcoming one with Matt Wright's group at RIT on defense against website fingerprinting attacks.

All of these collaborations are great, but there are precious few people on the Tor side who are keeping up with them, and those people need to balance their research time with development, advocacy, management, etc. I'm really looking forward to the time where Tor can have an actual research department.

And lastly, I would be remiss in describing our academic collaborations without also including a shout-out to the many universities that are running exit relays to help the network grow. As professor Leo Reyzin from Boston University once explained for why it is appropriate for his research lab to support the Tor network, "If biologists want to study elephants, they get an elephant. I want my elephant." So, special thanks to Boston University, University of Michigan, University of Waterloo, MIT, CMU (their computer science department that is), University of North Carolina, University of Pennsylvania, Universidad Galileo, and Clarkson University. And if you run an exit relay at a university but you're not on this list, please reach out!

Part three: The Privacy Enhancing Technologies Symposium

Another critical part of the privacy research world is the Privacy Enhancing Technologies Symposium (PETS), which is the premiere venue for technical privacy and anonymity research. This yearly gathering started as a workshop in 2000, graduated to being called a symposium in 2008, and in 2015 it became an open-access journal named Proceedings on Privacy Enhancing Technologies.

The editorial board and chairs for PETS over the years overlap greatly with the Tor community, with a lot of names you'll see at both PETS and the Tor twice-yearly meetings, including Nikita Borisov, George Danezis, Claudia Diaz, Roger Dingledine (me), Ian Goldberg, Rachel Greenstadt, Kat Hanna, Nick Hopper, Steven Murdoch, Paul Syverson, and Matt Wright.

But beyond community overlap, The Tor Project is actually the structure underneath PETS. The group of academics who run the PETS gatherings intentionally did not set up corporate governance and all those pieces of bureaucracy that drag things down — so they can focus on having a useful research meeting each year — and Tor stepped in to effectively be the fiscal sponsor, by keeping the bank accounts across years, and by being the "owner" for the journal since De Gruyter's paperwork assumes that some actual organization has to own it. We're proud that we can help provide stability and longevity for PETS.

Speaking of all these papers: we have tracked the most interesting privacy and anonymity papers over the years on the anonymity bibliography (anonbib). But at this point, anonbib is still mostly a two-man show where Nick Mathewson and I update it when we find some spare time, and it's starting to show its age since its launch in 2003, especially with the huge growth in the field, and with other tools like Google Scholar. Probably the best answer is that we need to trim it down so it's more of a "recommended reading list" than a resource of all relevant papers. If you want to help, let us know!

Part four: The Tor Research Safety Board

This post is running long, so I will close by pointing to the Tor Research Safety Board, a group of researchers who study Tor and who want to minimize privacy risks while fostering a better understanding of the Tor network and its users. That page lists a set of guidelines on what to consider when you're thinking about doing research on Tor users or the Tor network, and a process for getting feedback and suggestions on your plan. We did a soft launch of the safety board this past year in the rump session at PETS, and we've fielded four requests for advice so far. We've been taking it slow in terms of publicity, but if you're a researcher and you can help us refine our process, please take a look!