Abstract

Evaluation of predicates on the state of a distributed system is complicated b y the lack of either a common clock or common memory. I n these systems, message passing is often used to order local events globally. This leads to a partial, causal ordering of system events. Predicate evaluation algorithms based on this causal ordering generally cannot determine if an unstable predicate was true at some instani! of real time without freezing the underlying application. They only determine whether or not the predicate could have occurred. This ordering is suficient f o r evaluating stable predicates, but algorithms based on it require a good deal of message passing.I n this paper, we present two algorithms which conclusively evaluate both stable and a restricted class of unstable predicates for a given execution. The algorithms are based on the use of roughly synchronized clocks. We present an algorithm for sche,duled evaluation as well as a centralized detection algorithm.

No abstract

A mutual anonymity system enables communication between a client and a service provider without revealing their identities. In general, the anonymity guarantees made by the protocol are enhanced when a large number of participants are recruited into the anonymity system. Peer-to-peer (P2P) systems are able to attract a large number of nodes and hence are highly suitable for anonymity systems. However, the churn (changes in system membership) within P2P networks, poses a significant challenge for low-bandwidth reliable anonymous communication in these networks. This paper presents MuON, a protocol to achieve mutual anonymity in unstructured P2P networks. MuON leverages epidemic-style data dissemination to deal with churn. Simulation results and security analysis indicate that MuON provides mutual anonymity in networks with high churn, while maintaining predictable latencies, high reliability, and low communication overhead.

No abstract