There have been a number of protocols proposed for anonymous network communication. In this paper we investigate attacks by corrupt group members that degrade the anonymity of each protocol over time. We prove that when a particular initiator continues communication with a particular responder across path reformations, existing protocols are subject to the attack. We use this result to place an upper bound on how long existing protocols, including Crowds, Onion Routing, Hordes, and DC-Net, can maintain anonymity in the face of the attacks described. Our results show that fully-connected DC-Net is the most resilient to these attacks, but it su ers from scalability issues that keep anonymity group sizes small. Additionally, we show how violating an assumption of the attack allows malicious users to setup other participants to falsely appear to be the initiator of a connection.

this paper we investigate attacks by corrupt group members that degrade the anonymity of each protocol over time. We prove that when a particular initiator continues communication with a particular responder across path reformations, existing protocols are subject to the attack. We use this result to place an upper bound on how long existing protocols, including Crowds, Onion Routing, Hordes, Web Mixes, and DC-Net, can maintain anonymity in the face of the attacks described. This provides a basis for comparing these protocols against each other. Our results show that fully-connected DC-Net is the most resilient to these attacks, but it su#ers from scalability issues that keep anonymity group sizes small. We also show through simulation that the underlying topography of the DC-Net has a#ects the resilience of the protocol: as the number of neighbors a node has increases both the communications overhead and the strength of the protocol increase

Among all the security issues in Voice over IP (VoIP) communications, one of the most difficult to achieve is traffic analysis resistance. Indeed, classical approaches provide a reasonable degree of security but induce large roundtrip times that are incompatible with VoIP. In this paper, we describe some of the privacy and security issues derived from traffic analysis in VoIP. We also give an overview of how to provide low-latency VoIP communication with strong resistance to traffic analysis. Finally, we present a server which can provide such resistance to hundreds of users even if the server is compromised.