Peer-to-peer (p2p) systems have the potential to harness huge amounts of resources. Unfortunately, however, it has been shown that most of today’s p2p networks suffer from a large fraction of free-riders, who consume resources without contributing much to the system themselves. This results in an overall performance degradation, and hence proper incentives are needed to encourage contributions. One interesting resource is bandwidth. Thereby, a service differentiation approach seems appropriate, where peers contributing higher upload bandwidths are rewarded with higher download bandwidths in return. Keeping track of the contribution of each peer in an open, decentralized environment, however, is a difficult task; many proposed systems are susceptible to false reports. Besides being prone to attacks, some solutions have a large communication and computation overhead, which can even be linear in the number of transactions—an unacceptable burden in practical and active systems. In this paper, we propose a reputation system which is robust to false reports and overcomes this scaling problem. Our results are promising, indicating that the mechanism is accurate and efficient especially when applied in systems where there are lots of transactions. For a more detailed technical report, we refer the reader to the TIK Report 246 (available at http://www.tik.ee.ethz.ch/).

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