Preventing Misbehavior in Cooperative Distributed Systems
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2009-12-01
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Abstract
Cooperative distributed systems are becoming increasingly popular as alternatives to the traditional client-server model for many applications, including file sharing, streaming, and distributed computing. In cooperative distributed systems, participants directly cooperate with each other to achieve common goals by sharing resources without the need of any central control. Therefore, in contrast to the client-server model, the system capacity potentially scales as the number of participants in a system increases, providing the participants with information or services with few resource restrictions. The information or services provided by the system can be thought of as a public good, and participants should play a part in the protection and provision of the public good. Thus, cooperation among participants to obtain mutual benefits is the fundamental premise behind the success of such a system.
In spite of the importance of cooperation among participants to protect and support the public goods in cooperative distributed systems, a high level of informational integrity of the goods and behavioral integrity of participants toward the goods is difficult to achieve due to malicious or selfish participants. Because such malicious or selfish behavior was not anticipated at the inception of cooperative distributed applications, they are highly vulnerable to such behavior. To address the problem, in this dissertation, we identify two major threats (i.e., pollution and free-riding) to the protection and provision of the public goods, and propose tailored solutions to those specific threats. In addition, a general, fairness-enforcing incentive mechanism is proposed to foster cooperation among participants, which could be readily used to prevent various misbehaviors in a wide range of cooperative distributed systems.
Firstly, this dissertation investigates the pollution problem in file sharing systems, and proposes a novel Distributed Hash Table (DHT)-based anti-pollution scheme called winnowing. Winnowing attempts to achieve a high level of informational integrity of the public goods (i.e., shared files in this case) through cooperation among (benign) participants. To attain the goal, publish verification and privacy-preserving object reputation are integrated into DHT as a part of publish and look-up processes.
Secondly, this dissertation presents a free-riding prevention mechanism in one of the most famous file sharing systems (i.e., BitTorrent), which depends on the use of secret sharing. By employing secret sharing into file sharing, the proposed scheme, called Treat-Before-Trick (TBeT), enforces cooperation among participants by restricting uncooperative participants from the acquisition of secrets required to complete their work. Therefore, a high level of behavioral integrity on the part of participants toward the public goods can be achieved under TBeT.
Finally, this dissertation proposes a general incentive mechanism which can be readily and widely used in many cooperative distributed systems to enforce cooperation among participants, which is named Triangle Chaining (T-Chain). T-Chain strongly depends both on the use of light-weight symmetric cryptography to reduce the opportunity for free-riding, and on the pay-it-forward policy to exploit the potential of multi-lateral participant compatibility.
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Keywords
free-riding, distributed systems, peer-to-peer, misbehavior, cooperation, incentive
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Degree
PhD
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Computer Science
