“Fellow finalists from the Department of Computer Science at Brown University in the US were recognised for a different privacy aspect — maintaining anonymity while ensuring accountability. Mira Belenkiy, Melissa Chase, C. Chris Erway, John Jannotti, Alptekin Küpçü, Anna Lysyanskaya and Erich Rachlin focused on peer-to-peer (P2P) systems, such as the popular BitTorrent file-sharing service. These types of services rely on every user’s computer providing service as well as receiving services from others. The decentralised nature of peer-to-peer systems makes it difficult to ensure that all computers are providing their fair share of service.

Although privacy and accountability may seem contradictory, the team has found a way to enable this by using advanced cryptography techniques, which they also developed. The proposed approach is analogous to using electronic cash (e-cash) for payment for online services. E-cash systems are designed to be anonymous like real cash, but can also be engineered with mechanisms to inhibit cheating. Here, the currency of e-cash is not monetary value, but levels of trust within a P2P network. The authors explored the economic issues that would be involved in a real deployment in a system like BitTorrent, and evaluated the performance of the system in both simulation and testing of a prototype implementation. The team used computer equipment that is considered basic by today’s standards, and concludes that provably secure, anonymous and scalable P2P systems are within reach.