Peer-to-peer systems have been proposed for a wide variety of applications, including file-sharing, web caching, distributed computation, cooperative backup, and onion routing. An important motivation for such systems is self-scaling; that is, the notion that increased participation increases the capacity of the system. Unfortunately, this property is at risk from selfish participants, as the decentralized nature of peer-to-peer systems makes accounting difficult. We use e-cash as a practical way to achieve accountability in peer-to-peer systems while maintaining their ability to self-scale.

E-cash is a natural fit for peer-to-peer systems that attempt to provide (or preserve) privacy for their participants, as it can be used to provide accountability without compromising the existing privacy goals of a peer-to-peer system. We applied e-cash to the file sharing scenario, and showed that it can be used in practice to provide the benefits mentioned above.

Our approach includes using a cryptographic programming language and interpreter to provide a set of cryptographic protocols, while also using various optimizations at the compiler level to reduce the computational and communication costs of anonymous e-cash transactions. We furthermore have made system design choices with the goal of reducing overhead and distributing load. We employ techniques from cryptography, networking, distributed systems, peer-to-peer systems, game theory, and mechanism design in our solutions.

Overall, our goal is to demonstrate that provably secure, anonymous, and scalable peer-to-peer systems are within reach.


Sarah Meiklejohn, C. Chris Erway, Alptekin Küpçü, Theodora Hinkle, Anna Lysyanskaya. ZKPDL: A Language-Based System for Efficient Zero-Knowledge Proofs and Electronic Cash. In USENIX Security 2010, Washington, DC, USA, August 2010.

Alptekin Küpçü, Anna Lysyanskaya. Usable Optimistic Fair Exchange. (CT-RSA 2010).

Alptekin Küpçü, Anna Lysyanskaya. Optimistic Fair Exchange with Multiple Arbiters. (PODC 2009 brief announcement and ESORICS 2010 full paper).

Mira Belenkiy, Melissa Chase, C. Chris Erway, John Jannotti, Alptekin Küpçü, Anna Lysyanskaya. Incentivizing Outsourced Computation. In Proceedings of the 2008 Workshop on the Economics of Networks, Systems, and Computation (NetEcon 2008), Seattle, WA, USA, August 2008.

Mira Belenkiy, Melissa Chase, C. Chris Erway, John Jannotti, Alptekin Küpçü, Anna Lysyanskaya, Eric Rachlin. Making P2P Accountable without Losing Privacy. In Proceedings of the 2007 ACM Workshop on Privacy in the Electronic Society (WPES 2007), Alexandria, VA, USA, October 2007.

Jan Camenisch, Anna Lysyanskaya, Mira Meyerovich. Endorsed E-Cash. In Proceedings of the 2007 IEEE Symposium on Security and Privacy (S&P 2007).

Jan Camenisch, Susan Hohenberger, Anna Lysyanskaya. Compact E-Cash. Eurocrypt 2005.