Special Issue: Recent Advances in Peer‐to‐Peer Systems and Security

Abstract

MOTIVATION AND BACKGROUNDPeer-to-peer systems have revolutionized the way we store [1,2], disseminate [3,4] and share [5,6] content. In recent years, researchers have examined numerous aspects of these innovative architectures and proposed numerous protocols and applications. While peer-to-peer research has impacted a number of areas, including theory, networking, databases and distributed systems, recent work has focused more on the issues of practical, deployable systems, measurements, and issues of security and privacy in peer-to-peer applications.This issue brings together recent work on several projects focused on building robust, practical peer-to-peer systems. The work described has also been presented at the 5th international workshop on peer-to-peer systems (IPTPS 2006), an annual forum for researchers and practitioners of large distributed systems, held in Santa Barbara, California, and attended by more than 80 participants. The goal of the workshop was to examine peer-to-peer technologies, applications and systems, and to identify key research issues and challenges that lie ahead. In the context of this workshop, peerto-peer systems were characterized as being decentralized, self-organizing distributed systems, in which all or most communication is symmetric. CONTENTSThis issue includes five papers, two of which [7,8] present novel approaches to enhance the efficiency of current file-sharing networks, while the other three [9-11] examine security-related issues including reputations, incentives and misbehaving users. In the first paper, Epema et al. [7] propose Tribler, a new content-sharing protocol that leverages social relationships to enhance performance. While Tribler leverages BitTorrent's downloading mechanism, it is primarily a social network, where users obtain persistent, long-term identities, and self-organize according to their preferences and operational history. By leveraging shared interests, Tribler encourages users to behave altruistically, and shows that with willing helpers, downloaders can dramatically reduce their download latencies. The second paper [8] proposes the novel application of a probabilistic counting algorithm to hybrid search. To estimate whether a file is popular, the authors propose that