Browsing by Subject "Tor"

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    Privacy and Performance Trade-offs in Anonymous Communication Networks
    (2017-02) Geddes, John
    Anonymous communication systems attempt to prevent adversarial eavesdroppers from learning the identities of any two parties communicating with each other. In order to protect from global adversaries, such as nation states and large internet service providers, systems need to induce large amounts of latency in order to sufficiently protect users identities. Other systems sacrifice protection against global adversaries in order to provide low latency service to their clients. This makes the system usable for latency sensitive applications like web browsing. In turn, more users participate in the low latency system, increasing the anonymity set for everybody. These trade-offs on performance and anonymity provided are inherent in anonymous communication systems. In this dissertation we examine these types of trade-offs in Tor, the most popular low latency anonymous communication system in use today. First we look at how user anonymity is affected by mechanisms built into Tor for the purpose of increasing client performance. To this end we introduce an induced throttling attack against flow control and traffic admission control algorithms which allow an adversarial relay to reduce the anonymity set of a client using the adversary as an exit. Second we examine how connections are managed for inter-relay communication and look at some recent proposals for more efficient relay communication. We show how some of these can be abused to anonymously launch a low resource denial of service attack against target relays. With this we then explore two potential solutions which provide more efficient relay communication along with preventing certain denial of service attacks. Finally, we introduce a circuit selection algorithm that can be used by a centralized authority to dramatically increase network utilization. This algorithm is then adapted to work in a decentralized manner allowing clients to make smarter decisions locally, increasing performance while having a small impact on client anonymity.
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    Privacy preserving performance enhancements for anonymous communication networks
    (2012-10) Jansen, Robert G.
    An anonymous communication system hides the fact that two parties are communicating, and as a result, drastically improves the online privacy of those using it. Tor is the most popular anonymous communication system deployed, but its popularity has illuminated problems with its design that have made it unbearably slow for many users who would otherwise benefit from its protections. These performance problems have been recognized, but there has been little work on designing and properly evaluating practical solutions that improve performance while also preserving privacy. We initiate an exploration into Tor's system design and the quality of the communication it provides. First, we design and develop a simulation tool, called Shadow, that allows us to experiment with the Tor software in a safe but realistic and controllable manner. We then give a precise model of the Tor network, the backbone networks upon which it operates, and the user agents operating within it. We show that by combining our model with Shadow, our experimentation environment is capable of producing network interactions and performance qualities indicative of real systems. We then investigate performance enhancements in three major areas of Tor's design. We explore Tor's utilization of resources by evaluating both existing and new circuit scheduling techniques, and show the extent to which scheduling can be used to prioritize traffic in order to improve desirable quality metrics. We then design and evaluate algorithms focused on reducing network load by throttling agents that consume an unfair share of network resources. Finally, in an effort to supplement Tor's volunteered resources, we design and analyze two schemes that increase network capacity by providing incentives to those contributing resources to the system.