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TU Berlin

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Peer-to-Peer Computing

Peer-to-peer computing is an interesting networking paradigm as it offers a high degree of scalability by exploiting the resources of the participants and avoids single-points of failures. Due to these desirable properties, peer-to-peer computing plays a crucial role in many networking applications beyond file-sharing, and the underlying ideas are also discussed as a design principle for the future Internet. Our research is concerned with the question of whether peer-to-peer is mature enough to step outside its "comfort zone". We conduct measurements of state-of-the-art peer-to-peer networks such as Kad and investigate the robustness, e.g., to Sybil attacks or selfish behavior. For example, we implemented the proof-of-concept BitTorrent client "BitThief" which provides evidence that despite the tit-for-tat incentive mechanism, free-riding is possible in BitTorrent. We develop algorithms to improve the performance of peer-to-peer systems: we devise peer-to-peer networks which are robust to worst-case churn (see e.g., our IPTPS paper), which allow for efficient joins and leaves (see e.g., our SHELL system at ICALP), or which are robust to denial of service attacks (see e.g., our Chameleon system at SPAA). Some of these algorithms were successfully implemented in the online storage tool Wuala and the streaming tool Streamforge, two Swiss startups.

Selected Publications

A DoS-Resilient Information System for Dynamic Data Management
Citation key BSS-DRISDDM-09
Author Baumgart, Matthias and Scheideler, Christian and Schmid, Stefan
Title of Book 21st ACM Symposium on Parallelism in Algorithms and Architectures (SPAA)
Pages 300–309
Year 2009
ISBN 978-1-60558-606-9
DOI http://dx.doi.org/10.1145/1583991.1584064
Location Calgary, Alberta, Canada
Month August
Abstract Denial of service (DoS) attacks are arguably one of the most cumbersome problems in the Internet. This paper presents a distributed information system (over a set of completely connected servers) called Chameleon which is robust to DoS attacks on the nodes as well as the operations of the system. In particular, it allows nodes to efficiently look up and insert data items at any time, despite a powerful ``past-insider adversary'' which has complete knowledge of the system up to some time point t0 and can use that knowledge in order to block a constant fraction of the nodes and inject lookup and insert requests to selected data. This is achieved with a smart randomized replication policy requiring a polylogarithmic overhead only and the interplay of a permanent and a temporary distributed hash table. All requests in Chameleon can be processed in polylog-arithmic time and work at every node.
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