Reducing call blocking rates for anonymous voice over IP communications

Schatz, David; Rossberg, Michael; Schaefer, Guenter

doi:10.1109/icumt.2017.8255174

Cited by 4 publications

(4 citation statements)

References 18 publications

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“…Prior efforts on anonymous calling [7,13,22,38] unanimously agree with aforementioned shortcomings of Tor. Some conclude this based on potentially biased results [36], involving relays only in Europe or only conducted a few hundred calls [13], lacking diversity.…”

Section: Introductionmentioning

confidence: 89%

“…Overall, a major hindrance in the wide-scale adoption (and availability) of such systems, is the recruitment of new volunteered relays and users (which Tor already has in abundance). Schatz et al [38] also highlight this issue. Additionally, as previously mentioned, prior evaluations over Tor, provide very few insights as to how the interplay of network performance attributes affects the voice call quality.…”

Section: Prior Effortsmentioning

confidence: 97%

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The Road Not Taken: Re-thinking the Feasibility of Voice Calling Over Tor

Sharma

Chaudhary

Hassija

et al. 2020

Proceedings on Privacy Enhancing Technologies

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Anonymous VoIP calls over the Internet holds great significance for privacy-conscious users, whistle-blowers and political activists alike. Prior research deems popular anonymization systems like Tor unsuitable for providing the requisite performance guarantees that real-time applications like VoIP need. Their claims are backed by studies that may no longer be valid due to constant advancements in Tor. Moreover, we believe that these studies lacked the requisite diversity and comprehensiveness. Thus, conclusions from these studies, led them to propose novel and tailored solutions. However, no such system is available for immediate use. Additionally, operating such new systems would incur significant costs for recruiting users and volunteered relays, to provide the necessary anonymity guarantees.It thus becomes an imperative that the exact performance of VoIP over Tor be quantified and analyzed, so that the potential performance bottlenecks can be amended. We thus conducted an extensive empirical study across various in-lab and real world scenarios to shed light on VoIP performance over Tor. In over half a million calls spanning 12 months, across seven countries and covering about 6650 Tor relays, we observed that Tor supports good voice quality (Perceptual Evaluation of Speech Quality (PESQ) >3 and one-way delay <400 ms) in more than 85% of cases. Further analysis indicates that in general for most Tor relays, the contentions due to cross-traffic were low enough to support VoIP calls, that are anyways transmitted at low rates (<120 Kbps). Our findings are supported by concordant measurements using iperf that show more than the adequate available bandwidth for most cases. Hence, unlike prior efforts, our research reveals that Tor is suitable for supporting anonymous VoIP calls.

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Section: Introductionmentioning

confidence: 89%

Section: Prior Effortsmentioning

confidence: 97%

The Road Not Taken: Re-thinking the Feasibility of Voice Calling Over Tor

Sharma

Chaudhary

Hassija

et al. 2020

Proceedings on Privacy Enhancing Technologies

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“…Schatz et al [18] improve another aspect of Herd: Instead of using a full mesh for static padding, they suggest to pad fewer links in total. Due to the statistical multiplexing gain, more active calls can be supported (fewer calls are blocked due to saturated links).…”

Section: Related Workmentioning

confidence: 99%

“…subject to constraints (1) -( 8) and ( 16) (18) Our rationale for being more "greedy" here is to compensate for the additional delays introduced by the de-jitter buffers. Again, the latency of the entry and rendezvous links is not modeled.…”

Section: 35mentioning

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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