Exploring challenges concerning reliable and scalable operation of large distributed systems. Developing reputation mechanisms to enhance network resilience to attacks. Studying the impact of social networks on Web 2.0 communities and marketplaces.

Publications

    Workshops

• Gayatri Swamynathan, Christo Wilson, Bryce Boe, Ben Zhao and Kevin Almeroth. "Do Social Networks improve e-Commerce? A Study on Social Marketplaces." Proceedings of The 1st ACM SIGCOMM Workshop on Online Social Networks (WOSN), August 2008 [pdf]

Abstract. Social networks have made a significant impact on how today's Internet users communicate, search for and share data. Numerous proposals have been made to improve existing distributed systems by leveraging the inherent trust built into social links. Many believe that augmenting online marketplaces with social networking should improve trust between transaction partners and improve user satisfaction. In this paper, we perform a detailed study of Overstock Auctions, a novel auction site that integrates social links into user profiles. Using data on connections between roughly 399,000 Overstock users, we evaluate the impact of social connections on business transactions. Our results show that while the majority of users do not engage in social networking, those who transact with friends of friends generally obtain significantly benefits in the form of higher user satisfaction.

• Gayatri Swamynathan, Ben Zhao and Kevin Almeroth. "Exploring the Feasibility of Proactive Reputations." Proceedings of The 5th International Workshop on Peer-to-Peer Systems (IPTPS), February 2006 [pdf]

Abstract. Reputation mechanisms help peers in a peer-to-peer (P2P) system avoid unreliable or malicious peers. In application-level networks, however, short peer lifetimes mean reputations are often generated from a small number of past transactions. These reputation values are less reliable, and more vulnerable to badmouthing or collusion attacks. We address this issue by introducing proactive reputations, a firsthand history of transactions initiated to augment incomplete or short-term reputation values. We present several mechanisms for generating proactive reputations, along with a statistical similarity metric to measure their effectiveness.

• Gayatri Swamynathan, Ben Zhao and Kevin Almeroth. "Decoupling Service and Feedback Trust in a Peer-to-Peer Reputation System." Proceedings of the 2005 International Workshop on Applications and Economics of Peer-to-Peer Systems, November 2005 [pdf]

Abstract. Reputation systems help peers decide whom to trust before undertaking a transaction. Conventional approaches to reputation-based trust modeling assume that peers reputed to provide trustworthy service are also likely to provide trustworthy feedback. By basing the credibility of a peer's feedback on its reputation as a transactor, these models become vulnerable to malicious nodes that provide good service to badmouth targeted nodes. We propose to decouple a peer's reputation as a service provider from its reputation as a service recommender, making the reputation more robust to malicious peers. We show via simulations that a decoupled approach greatly enhances the accuracy of reputations generated, resulting in fewer malicious transactions, false positives, and false negatives.

• Gayatri Swamynathan, Ben Zhao, Kevin Almeroth and S. Rao Jammalamadaka. "Towards Reliable Reputations for Dynamic Networked Systems." Proceedings of the Symposium on Reliable Distributed Systems (SRDS), October 2008 [pdf]

  Abstract. A new generation of distributed systems and applications rely on the cooperation of diverse user populations motivated by self-interest. While they can utilize "reputation systems" to reduce selfish behaviors that disrupt or manipulate the network for personal gain, current reputations face a key challenge in large dynamic networks: vulnerability to peer collusion. In this paper, we propose to dramatically improve the accuracy of reputation systems with the use of a statistical metric that measures the "reliability" of a peer's reputation taking into account collusionlike behavior. Trace-driven simulations on P2P network traffic show that our reliability metric drastically improves system performance. We also apply our metric to 18,000 randomly selected eBay user reputation profiles, and surprisingly discover numerous users with collusion-like behaviors worthy of additional investigation.

• Gayatri Swamynathan, Tyler Close, Sujata Banerjee, Rick McGeer, Ben Zhao and Kevin Almeroth. "Scalable Access Control For Web Services." Proceedings of the 2007 Fifth International Conference on Creating, Connecting and Collaborating through Computing, January 2007 [pdf]

Abstract. Controlling access to a large, distributed web service is a potentially error prone process that may negatively impact request throughput and usability. Our Authorization-Based Access Control (or ABAC) URL rewriter solves this problem by providing locally verifiable authorizations and delegation tracking compatible with common web tools. Our access control mechanism is reusable, distributed and meets the scaling requirements of large distributed web services. We demonstrate the successful operation of our proposed mechanism on HP's real-time network monitoring and measurement web service, S³.

    Journals

• Gayatri Swamynathan, Ben Zhao and Kevin Almeroth. "Exploring the Feasibility of Proactive Reputations." Concurrency and Computation: Practice and Experience, Special Issue on Recent Advances in P2P Systems and Security. Vol. 20, No. 2, Pgs 155-166. May 2007 [pdf]

  Abstract. Reputation mechanisms help peers in a peer-to-peer system avoid unreliable or malicious peers. In application-level networks, however, short peer lifetimes mean reputations are often generated from a small number of past transactions. These reputation values are less "reliable", and more vulnerable to bad-mouthing or collusion attacks. We address this issue by introducing proactive reputations, a first-hand history of transactions initiated to augment incomplete or short-term reputation values.We present several mechanisms to generate proactive reputations, along with a statistical similarity metric to measure their effectiveness.

• Gayatri Swamynathan, Ben Zhao, Kevin Almeroth, and Heather Zheng. "Globally Decoupled Reputations for Large Distributed Networks." Advances in Multimedia. Vol. 2007, No. 1. Jan 2007 [pdf]
Abstract. Reputation systems help establish social control in peer-to-peer networks. To be truly effective, however, a reputation system should counter attacks that compromise the reliability of user ratings. Existing reputation approaches either average a peer's lifetime ratings or account for rating credibility by weighing each piece of feedback by the reputation of its source.While these systems improve cooperation in a P2P network, they are extremely vulnerable to unfair ratings attacks. In this paper, we recommend that reputation systems decouple a peer's service provider reputation from its service recommender reputation, thereby, making reputations more resistant to tampering. We propose a scalable approach to system-wide decoupled service and feedback reputations and demonstrate the effectiveness of our model against previous nondecoupled reputation approaches. Our results indicate that decoupled approache significantly improves reputation accuracy, resulting in more successful transactions. Furthermore, we demonstrate the effectiveness and scalability of our decoupled approach as compared to PeerTrust, an alternative mechanism proposed for decoupled reputations. Our results are compiled from comprehensive logs collected fromMaze, a large file-sharing system with over 1.4 million users supporting searches on 226TB of data.

• Building Reliable Reputation Systems: A Survey. Work in Submission.

PhD Defense

• Defense Slides
• Thesis Abstract

PhD Proposal

• Proposal Abstract

Major Area Examination

• Abstract
• MAE Documents

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