One-out-of-Many Proofs: Or How to Leak a Secret and Spend a Coin

I’m going to EUROCRYPT 2015 to present a new zero-knowledge proof that I’ve developed together with Markulf Kohlweiss from Microsoft Research. Zero-knowledge proofs enable you to demonstrate that a particular statement is true without revealing anything else than the fact it is true. In our case the statements are one-out-of-many statements, intuitively that out of a number of items one of them has a special property, and we greatly reduce the size of the proofs compared to previous works in the area. Two applications where one-out-of-many proofs come in handy are ring signatures and Zerocoin.

Ring signatures can be used to sign a message anonymously as a member of a group of people, i.e., all a ring signature says is that somebody from the group signed the message but not who it was. Consider for instance a whistleblower who wants to leak her company is dumping dangerous chemicals in the ocean, yet wants to remain anonymous due to the risk of being fired. By using a ring signature she can demonstrate that she works for the company, which makes the claim more convincing, without revealing which employee she is. Our one-out-of-many proofs can be used to construct very efficient ring signatures by giving a one-out-of-many proof that the signer holds a secret key corresponding to a public key for one of the people in the ring.

Zerocoin is a new virtual currency proposal where coins gain value once they’ve been accepted on a public bulletin board. Each coin contains a commitment to a secret random serial number that only the owner knows. To anonymously spend a coin the owner publishes the serial number and gives a one-out-of-many proof that the serial number corresponds to one of the public coins. The serial number prevents double spending of a coin; nobody will accept a transaction with a previously used serial number. The zero-knowledge property of the one-out-of-many proof provides anonymity; it is not disclosed which coin the serial number corresponds to. Zerocoin has been suggested as a privacy enhancing add-on to Bitcoin.

The full research paper is available on the Cryptology ePrint Archive.

MSc Information Security @UCL

As the next programme director of UCL’s MSc in Information Security, I have quickly realized that showcasing a group’s educational and teaching activities is no trivial task.

As academics, we learn over the years to make our research “accessible” to our funders, media outlets, blogs, and the likes. We are asked by the REF to explain why our research outputs should be considered world-leading and outstanding in their impacts. As security, privacy, and cryptography researchers, we repeatedly test our ability to talk to lawyers, bankers, entrepreneurs, and policy makers.

But how do you do good outreach when it comes to postgraduate education? Well, that’s a long-standing controversy. The Economist recently dedicated a long report on tertiary education and also discussed misaligned incentives in strategic decisions involving admissions, marketing, and rankings. Personally, I am particularly interested in exploring ways one can (attempt to) explain the value and relevance of a specialist masters programme in information security. What outlets can we rely on and how do we effectively engage, at the same time, current undergraduate students, young engineers, experienced professionals, and aspiring researchers? How can we shed light on our vision & mission to educate and train future information security experts?

So, together with my colleagues of UCL’s Information Security Group, I started toying with the idea of organizing events — both in the digital and the analog “world” — that could provide a better understanding of both our research and teaching activities. And I realized that, while difficult at first and certainly time-consuming, this is a noble, crucial, and exciting endeavor that deserves a broad discussion.


Information Security: Trends and Challenges

Thanks to the great work of Steve Marchant, Sean Taylor, and Samantha Webb (now known as the “S3 team” :-)), on March 31st, we held what I hope is the first of many MSc ISec Open Day events. We asked two of our friends in industry — Alec Muffet (Facebook Security Evangelist) and Dr Richard Gold (Lead Security Analyst at Digital Shadows and former Cisco cloud web security expert) — and two of  our colleagues — Prof. Angela Sasse and Dr David Clark — to give short, provocative talks about what they believe trends and challenges in Information Security are. In fact, we even gave it a catchy name to the event: Information Security: Trends and Challenges.

Continue reading MSc Information Security @UCL