Relay selection in wireless networks for optimal delay anonymity tradeoff

Wireless networks are susceptible to eavesdropping by unauthorized intruders who aim to extract information about the networked exchanges. Even when packets are encrypted, unsophisticated energy detectors can be used to identify the source destination pairs using the packet transmission timing on the wireless medium. Anonymous network protocols aim to prevent this information retrieval through the use of special intermediate relays that add artificial delays so as to confuse the eavesdropper. Previous studies have demonstrated that a tradeoff exists between the anonymity- secrecy of source destination pairs from timing analysis- provided by such relays and the latency incurred. The focus of this work is the tradeoff between anonymity and delay when a network of such relays are employed, as in practical anonymous systems such as Tor. Specifically, the problem of best route selection in anonymous networks that optimally trades off delay for anonymity has been investigated in this work. Using Shannon Entropy as the metric of anonymity, sufficient conditions on network parameters to achieve maximum anonymity are derived. The optimal route selection algorithm to obtain a desired tradeoff is shown to be computationally impractical, and a suboptimal route selection algorithm that effectively balances delay and anonymity has been proposed which has a negligible gap to the optimal solution, but requires far less computational resources. An incremental optimization which allows for real time addition of new users to the anonymous system is investigated and the performance compared with the centralized schemes.