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.
University of Minnesota Ph.D. dissertation. October 2012. Major Computer science. Advisor: Nicholas J. Hopper. 1 computer file (PDF); xi, 199 pages.
Jansen, Robert G..
Privacy preserving performance enhancements for anonymous communication networks.
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