Sergio Marti

Mitigating routing misbehavior in mobile ad hoc networks

This paper describes two techniques that improve throughput in an ad hoc network in the presence of nodes that agree to forward packets but fail to do so. To mitigate this problem, we propose categorizing nodes based upon their dynamically measured behavior. We use a watchdog that identifies misbehaving nodes and a pathrater that helps routing protocols avoid these nodes. Through simulation we evaluate watchdog and pathrater using packet throughput, percentage of overhead (routing) transmissions, and the accuracy of misbehaving node detection. When used together in a network with moderate mobility, the two techniques increase throughput by 17% in the presence of 40% misbehaving nodes, while increasing the percentage of overhead transmissions from the standard routing protocols 9% to 17%. During extreme mobility, watchdog and pathrater can increase network throughput by 27%, while increasing the overhead transmissions from the standard routing protocols 12% to 24%.

Taxonomy of trust: Categorizing P2P reputation systems

The field of peer-to-peer reputation systems has exploded in the last few years. Our goal is to organize existing ideas and work to facilitate system design. We present a taxonomy of reputation system components, their properties, and discuss how user behavior and technical constraints can conflict. In our discussion, we describe research that exemplifies compromises made to deliver a useable, implementable system.

Limited reputation sharing in P2P systems

The increasing popularity of resource exchange through peer-to-peer networks has encouraged the development of ways to support more complex commercial transactions over these networks. Unfortunately, the prospect of higher volume and higher value transactions attracts agents seeking to exploit or weaken the network by propagating bad information and services. This paper presents advantages and disadvantages of resource selection techniques based on peer reputation. We evaluate the effect of limited reputation information sharing on the efficiency and load distribution of a peer-to-peer system. We show that limited reputation sharing can reduce the number of failed transactions by a factor of 20.

DHT routing using social links

The equality and anonymity of peer-to-peer networks makes them vulnerable to routing denial of service attacks from misbehaving nodes. In this paper, we investigate how existing social networks can benefit P2P networks by leveraging the inherent trust associated with social links. We present a trust model that lets us compare routing algorithms for P2P networks overlaying social networks. We propose SPROUT, a DHT routing algorithm that significantly increases the probability of successful routing by using social links. Finally, we discuss further optimization and design choices for both the model and the routing algorithm.

SPROUT: P2P routing with social networks

In this paper, we investigate how existing social networks can benefit P2P data networks by leveraging the inherent trust associated with social links We present a trust model that lets us compare routing algorithms for P2P networks overlaying social networks.We propose SPROUT, a DHT routing algorithm that, by using social links, significantly increases the number of query results and reduces query delays.We discuss further optimization and design choices for both the model and the routing algorithm Finally, we evaluate our model versus regular DHT routing and Gnutella-like flooding.

Identity crisis: anonymity vs reputation in P2P systems

The effectiveness of reputation systems for peer-to-peer resource-sharing networks is largely dependent on the reliability of the identities used by peers in the network. Much debate has centered around how closely ones pseudo-identity in the network should be tied to their real-world identity, and how that identity is protected from malicious spoofing. We investigate the cost in efficiency of two solutions to the identity problem for peer-to-peer reputation systems. Our results show that, using some simple mechanisms, reputation systems can provide a factor of 4 to 20 improvement in performance over no reputation system, depending on the identity model used.

Peer-to-peer research at Stanford

n this paper we present recent and ongoing research projects of the Peers research group at Stanford University.

Quantifying agent strategies under reputation

Our research proposes a simple buyer/seller game that captures the incentives dictating the interaction between peers in resource trading peer-to-peer networks. We prove that for simple reputation-based buyer strategies, a sellers decision whether to cheat or not is dependent only on the length of its transaction history, not on the particular actions committed. Given a finite number of transactions, a peer can compute a utility optimal sequence of cooperations and defections. With the limited information provided by many reputation systems, a peer has incentive to defect on a large fraction of its transactions. If temporal information is used, equilibrium is reached when peers predominantly cooperate.

Authenticity and availability in PIPE networks

We describe a system, which we call a peer-to-peer information preservation and exchange (PIPE) network, for protecting, digital data collections from failure. A significant challenge in such networks is ensuring that documents are replicated and accessible despite malicious sites which may delete data, refuse to serve data, or serve an altered version of the data. We enumerate the services of PIPE networks, discuss a threat model for malicious sites, and propose basic solutions for managing these malicious sites. The basic solutions are inefficient, but demonstrate that a secure system can be built. We also sketch ways to improve efficiency.