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IEEE/ACM Trans. Netw. 01/2005; 13:1121-1134.
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ABSTRACT: Eigenvector based methods in general, and Google’s PageRank algorithm for rating web pages in particular, have become an important
component of information retrieval on the Web. In this paper, we study the efficacy of, and countermeasures for, collusions designed to improve user rating in such systems.
We define a metric, called the amplification factor, which captures the amount of PageRank-inflation obtained by a group due
to collusions. We prove that the amplification factor can be at most 1/ε, where ε is the reset probability of the PageRank random walk. We show that colluding nodes (e.g., web-pages) can achieve this amplification
and increase their rank significantly in realistic settings; further, several natural schemes to address this problem are
demonstrably inadequate.
We propose a relatively simple modification to PageRank which renders the algorithm insensitive to such collusion attempts.
Our scheme is based on the observation that nodes which cheat do so by “stalling” the random walk in a small portion of the
web graph and, hence, their PageRank must be especially sensitive to the reset probability ε. We perform exhaustive simulations on the Web graph to demonstrate that our scheme successfully prevents colluding nodes
from improving their rank, yielding an algorithm that is robust to gaming.
11/2004: pages 92-104;
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ABSTRACT: There exist many successful examples of online reputation (or rating) systems, such as on-line markets and e-tailer ratings. However, for peer-to-peer applications, an explicit ratings subsystem has often been ignored in system design because of the implicit assumption of trust and altruism among P2P users. This assumption might be true (or might not matter) when a P2P network is still in its infancy and is relatively small in size. But the assumption might break down with increase in the size and diversity of the P2P network. In this paper, we discuss issues in the design of rating schemes for P2P systems. In keeping with the design philosophy of many of these system, we consider the design of distributed rating systems. As a case study, we illustrate two different approaches to a distributed rating system aimed at tackling the free-rider problem in P2P networks. A key challenge in designing such rating schemes is to make them collusion-proof: we discuss our efforts in this direction. I.
06/2004;
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Computer Communication Review. 01/2004; 35:93-97.
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Algorithms and Models for the Web-Graph: Third International Workshop, WAW 2004, Rome, Italy, October 16, 2004, Proceeedings; 01/2004
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[show abstract]
[hide abstract]
ABSTRACT: There exist many successful examples of online reputation (or rating) systems, such as on-line markets and e-tailer ratings. However, for peer-to-peer applications, an explicit ratings subsystem has often been ignored in system design because of the implicit assumption of trust and altruism among P2P users. This assumption might be true (or might not matter) when a P2P network is still in its infancy and is relatively small in size. But the assumption might break down with increase in the size and diversity of the P2P network. In this paper, we discuss issues in the design of rating schemes for P2P systems. In keeping with the design philosophy of many of these system, we consider the design of distributed rating systems. As a case study, we illustrate two different approaches to a distributed rating system aimed at tackling the free-rider problem in P2P networks. A key challenge in designing such rating schemes is to make them collusion-proof: we discuss our efforts in this direction. I.
06/2003;
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ABSTRACT: Distributed hash table (DHT) systems are an important class of peer-to-peer routing infrastructures. They enable scalable wide-area storage and retrieval of information, and will support the rapid development of a wide variety of Internet-scale applications ranging from naming systems and file systems to application-layer multicast. DHT systems essentially build an overlay network, but a path on the overlay between any two nodes can be significantly di#erent from the unicast path between those two nodes on the underlying network. As such, the lookup latency in these systems can be quite high and can adversely impact the performance of applications built on top of such systems.
05/2003;
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Proceedings of the International Conference on Measurements and Modeling of Computer Systems, SIGMETRICS 2003, June 9-14, 2003, San Diego, CA, USA; 01/2003
