Showing papers by "Paul Syverson published in 2011"

Trust-based anonymous communication: adversary models and routing algorithms

Abstract: We introduce a novel model of routing security that incorporates the ordinarily overlooked variations in trust that users have for different parts of the network. We focus on anonymous communication, and in particular onion routing, although we expect the approach to apply more broadly.This paper provides two main contributions. First, we present a novel model to consider the various security concerns for route selection in anonymity networks when users vary their trust over parts of the network. Second, to show the usefulness of our model, we present as an example a new algorithm to select paths in onion routing. We analyze its effectiveness against deanonymization and other information leaks, and particularly how it fares in our model versus existing algorithms, which do not consider trust. In contrast to those, we find that our trust-based routing strategy can protect anonymity against an adversary capable of attacking a significant fraction of the network.

Probabilistic Analysis of Onion Routing in a Black-box Model

Abstract: We perform a probabilistic analysis of onion routing. The analysis is presented in a black-box model of anonymous communication in the Universally Composable framework that abstracts the essential properties of onion routing in the presence of an active adversary that controls a portion of the network and knows all a priori distributions on user choices of destination. Our results quantify how much the adversary can gain in identifying users by exploiting knowledge of their probabilistic behavior. In particular, we show that, in the limit as the network gets large, a user u's anonymity is worst either when the other users always choose the destination u is least likely to visit or when the other users always choose the destination u chooses. This worst-case anonymity with an adversary that controls a fraction b of the routers is shown to be comparable to the best-case anonymity against an adversary that controls a fraction \surdb.

A peel of onion

Abstract: Onion routing was invented more than fifteen years ago to separate identification from routing in network communication. Since that time there has been much design, analysis, and deployment of onion routing systems. This has been accompanied by much confusion about what these systems do, what security they provide, how they work, who built them, and even what they are called. Here I give an overview of onion routing from its earliest conception to some of the latest research, including the design and use of Tor, a global onion routing network with about a half million users on any given day.