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Brownie Points Project

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, increased participation increases the capacity of the system. Unfortunately, this property is at risk from selfish participants. The decentralized nature of peer-to-peer systems makes accounting difficult. We use e-cash as a practical solution to the desire for 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. E-cash 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 a set of novel cryptographic protocols that mitigate the computational and communication costs of anonymous e-cash transactions, and system design choices that further reduce overhead and distribute load. We employ techniques from cryptography, networking, distributed systems, peer-to-peer systems, game theory, and mechanism design in our solutions.

This research project's goal is to show that provably secure, anonymous, and scalable peer-to-peer systems are within reach.

Project status: Active

Project Home Page: http://cs.brown.edu/research/brownie

Funding

Cyber Trust Grant, NSF, $350,000, 2006

Publications

Belenkiy, M., Chase, M., Erway, C. C., Jannotti, J., Küpçü, A., Lysyanskaya, A., and Rachlin, E. Making P2P Accountable without Losing Privacy. ACM Workshop On Privacy In The Electronic Society, ACM, pp. 31-40. 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, increased participation increases the capacity of the system. Unfortunately, this property is at risk from selfish participants. The decentralized nature of peer-to-peer systems makes accounting difficult. We show that e-cash can be a practical solution to the desire for accountability in peer-to-peer systems while maintaining their ability to self-scale. No less important, e-cash is a natural fit for peer-to-peer systems that attempt to provide (or preserve) privacy for their participants. We show that e-cash can be used to provide accountability without compromising the existing privacy goals of a peer-to-peer system. We show how e-cash can be practically applied to a file sharing application. Our approach includes a set of novel cryptographic protocols that mitigate the computational and communication costs of anonymous e-cash transactions, and system design choices that further reduce overhead and distribute load. We conclude that provably secure, anonymous, and scalable peer-to-peer systems are within reach. [ pdf ]

Jan Camenisch, Anna Lysyanskaya, M. M. Endorsed E-Cash. IEEE Symposium on Security and Privacy, IEEE, pp. 101-115. An electronic cash (e-cash) scheme lets a user withdraw money from a bank and then spend it anonymously. E-cash can be used only if it can be securely and fairly exchanged for electronic goods or services. In this paper, we introduce and realize endorsed e-cash. An endorsed e-coin consists of a lightweight endorsement x and the rest of the coin which is meaningless without x. We reduce the problem of exchanging e-cash to that of exchanging endorsements. We demonstrate the usefulness of endorsed e-cash by exhibiting simple and efficient solutions to two important problems: (1) optimistic and unlinkable fair exchange of e-cash for digital goods and services; and (2) onion routing with incentives and accountability for the routers. Finally, we show how to represent a set of n endorsements using just one endorsement; this means that the complexity of the fair exchange protocol for n coins is the same as for one coin, making e-cash all the more scalable and suitable for applications. Our fair exchange of multiple e-coins protocol can be applied to fair exchanges of (almost) any secrets. [ pdf ]

Camenisch, J., Hohenberger, S., and Lysyanskaya, A. Compact e-cash. In Proceedings of the 24th Annual International Conference on the Theory and Applications of Cryptographic Techniques (Eurocrypt 2005) (2005), R. Cramer, Ed., Springer, pp. 302-321. [ pdf ]