Large-scale Latency Measurements in the Tor Network

Schatz, David; Rossberg, Michael; Schaefer, Guenter

doi:10.5281/zenodo.4911583

Cited by 2 publications

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“…We further used their consensus weight as an estimate for their bandwidth in kB s −1 [17]. Our raw dataset and further details about pre-processing are also publicly available [20].…”

Section: Quantitative Evaluationmentioning

confidence: 99%

Optimizing Packet Scheduling and Path Selection for Anonymous Voice Calls

Schatz

Rossberg

Schaefer

2021

Proceedings of the 16th International Conference on Availability, Reliability and Security

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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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“…We further used their consensus weight as an estimate for their bandwidth in kB s −1 [17]. Our raw dataset and further details about pre-processing are also publicly available [20].…”

Section: Quantitative Evaluationmentioning

confidence: 99%

Optimizing Packet Scheduling and Path Selection for Anonymous Voice Calls

Schatz

Rossberg

Schaefer

2021

Proceedings of the 16th International Conference on Availability, Reliability and Security

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Hydra: Practical Metadata Security for Contact Discovery, Messaging, and Voice Calls

2022

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Protecting communications’ metadata can be as important as protecting their content, i.e., recognizing someone contacting a medical service may already allow to infer sensitive information. There are numerous proposals to implement anonymous communications, yet none provides it in a strong (but feasible) threat model in an efficient way. We propose Hydra, an anonymity system that is able to efficiently provide metadata security for a wide variety of applications. Main idea is to use latency-aware, padded, and onion-encrypted circuits even for connectionless applications. This allows to implement strong metadata security for contact discovery and text-based messages with relatively low latency. Furthermore, circuits can be upgraded to support voice calls, real-time chat sessions, and file transfers—with slightly reduced anonymity in presence of global observers. We evaluate Hydra using an analytical model as well as call simulations. Compared to other systems for text-based messaging, Hydra is able to decrease end-to-end latencies by an order of magnitude without degrading anonymity. Using a dataset generated by performing latency measurements in the Tor network, we further show that Hydra is able to support anonymous voice calls with acceptable quality of service in real scenarios. A first prototype of Hydra is published as open source.

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Large-scale Latency Measurements in the Tor Network

Cited by 2 publications

References 0 publications

Optimizing Packet Scheduling and Path Selection for Anonymous Voice Calls

Optimizing Packet Scheduling and Path Selection for Anonymous Voice Calls

Hydra: Practical Metadata Security for Contact Discovery, Messaging, and Voice Calls

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