To support position-dependent services, like matchmaking algorithms for online games or geographic backup routes, the estimation of peer locations became a key requisite for a range of applications, recently. However, exact localization may be impossible, e.g., due to nodes lacking Global Positioning System (GPS) access for reasons of cost, energy, or signal unavailability. Alternative approaches, e.g., by nearby WLAN BSSIDs or IP geolocation, rely on databases and normally contain large outliers, in particular when concerning underrepresented mapping locations. This led us to the study of a complementary idea: By embedding nodes on a sphere and periodically minimizing local positioning errors by delay-based multilateration, we efficiently estimate node positions by distributed means, given a fair amount of position hints. Based on simulations that rely on real-world PlanetLab latency data, we show that global-scope peer locations can be estimated with an accuracy of a few hundred kilometers, where the novel approach outperforms a previously proposed spring-mass-based method by about 50%.
Onion routing is a promising approach to implement anonymous voice calls. Uniform-sized voice packets are routed via multiple relays and encrypted in layers to avoid a correlation of packet content in different parts in the network. By using pre-built circuits, onion encryption may use efficient symmetric ciphers. However, if packets are forwarded by relays as fast as possible-to minimize end-to-end latency-network flow watermarking may still de-anonymize users. A recently proposed countermeasure synchronizes the start time of many calls and batch processes voice packets with the same sequence number in relays. However, if only a single link with high latency is used, it will also negatively affect latency of all other calls. This article explores the limits of this approach by formulating a mixed integer linear program (MILP) that minimizes latency "bottlenecks" in path selection. Furthermore, we suggest a different scheduling strategy for voice packets, i.e. implementing independent de-jitter buffers for all flows. In this case, a MILP is used to minimize the average latency of selected paths. For comparison, we solve the MILPs using latency and bandwidth datasets obtained from the Tor network. Our results show that batch processing cannot reliably achieve acceptable end-to-end latency (below 400 ms) in such a scenario, where link latencies are too heterogeneous. In contrast, when using de-jitter buffers for packet scheduling, path selection benefits from low latency links without degrading anonymity. Consequently, acceptable end-to-end latency is possible for a large majority of calls.
CCS CONCEPTS• Security and privacy → Privacy-preserving protocols.
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