Elan Pavlov

Supporting Privacy in Decentralized Additive Reputation Systems

Previous studies have been suggestive of the fact that reputation ratings may be provided in a strategic manner for reasons of reciprocation and retaliation, and therefore may not properly reflect the trustworthiness of rated parties. It thus appears that supporting privacy of feedback providers could improve the quality of their ratings. We argue that supporting perfect privacy in decentralized reputation systems is impossible, but as an alternative present three probabilistic schemes that support partial privacy. On the basis of these schemes, we offer three protocols that allow ratings to be privately provided with high probability in decentralized additive reputation systems.

A generic scheme for building overlay networks in adversarial scenarios

This paper presents a generic scheme for a central, yet untackled issue in overlay dynamic networks: maintaining stability over long life and against malicious adversaries. The generic scheme maintains desirable properties of the underlying structure including low diameter, and efficient routing mechanism, as well as balanced node dispersal. These desired properties are maintained in a decentralized manner without resorting to global updates or periodic stabilization protocols even against an adaptive adversary that controls the arrival and departure of nodes.

Minimum-Weight Spanning Tree Construction in O (log log n ) Communication Rounds

We consider a simple model for overlay networks, where all n processes are connected to all other processes, and each message contains at most O(log n) bits. For this model, we present a distributed algorithm which constructs a minimum-weight spanning tree in O(log log n) communication rounds, where in each round any process can send a message to every other process. If message size is

Single-value combinatorial auctions and algorithmic implementation in undominated strategies

\Theta(n^\epsilon)

An incentive-compatible multi-armed bandit mechanism

for some

MST construction in O (log log n ) communication rounds

\epsilon>0

Byzantine agreement in the full-information model in O(log n) rounds

, then the number of communication rounds is

Generalized trade reduction mechanisms

O(\log{1\over\epsilon})

Mechanisms for a spatially distributed market

.

Optimal Unconditional Information Diffusion

In this article, we are interested in general techniques for designing mechanisms that approximate the social welfare in the presence of selfish rational behavior. We demonstrate our results in the setting of Combinatorial Auctions (CA). Our first result is a general deterministic technique to decouple the algorithmic allocation problem from the strategic aspects, by a procedure that converts any algorithm to a dominant-strategy ascending mechanism. This technique works for any single value domain, in which each agent has the same value for each desired outcome, and this value is the only private information. In particular, for “single-value CAs”, where each player desires any one of several different bundles but has the same value for each of them, our technique converts any approximation algorithm to a dominant strategy mechanism that almost preserves the original approximation ratio. Our second result provides the first computationally efficient deterministic mechanism for the case of single-value multi-minded bidders (with private value and private desired bundles). The mechanism achieves an approximation to the social welfare which is close to the best possible in polynomial time (unless P=NP). This mechanism is an algorithmic implementation in undominated strategies, a notion that we define and justify, and is of independent interest.