arXiv subjects

Christoph Döpmann

Publications and source records attributed to Christoph Döpmann.

5 recordsLinked to original sources

arXiv2025

Progressive Pruning: Analyzing the Impact of Intersection Attacks

Stream-based communication dominates today's Internet, posing unique challenges for anonymous communication networks (ACNs). Traditionally designed for independent messages, ACNs struggle to account for the inherent vulnerabilities of streams, such as susceptibility to intersection attacks. In this work, we address this gap and introduce progressive pruning, a novel methodology for quantifying the susceptibility to intersection attacks. Progressive pruning quantifies and monitors anonymity sets over time, providing an assessment of an adversary's success in correlating senders and receivers. We leverage this methodology to analyze synthetic scenarios and large-scale simulations of the Tor network using our newly developed TorFS simulator. Our findings reveal that anonymity is significantly influenced by stream length, user population, and stream distribution across the network. These insights highlight critical design challenges for future ACNs seeking to safeguard stream-based communication against traffic analysis attacks.

cs.CR↗

arXiv2023

Modeling Tor Network Growth by Extrapolating Consensus Data

Since the Tor network is evolving into an infrastructure for anonymous communication, analyzing the consequences of network growth is becoming more relevant than ever. In particular, adding large amounts of resources may have unintentional consequences for the system performance as well as security. To this end, we contribute a methodology for the analysis of scaled Tor networks that enables researchers to leverage real-world network data. Based on historical network snapshots (consensuses), we derive and implement a model for methodically scaling Tor consensuses. This allows researchers to apply established research methods to scaled networks. We validate our model based on historical data, showing its applicability. Furthermore, we demonstrate the merits of our data-driven approach by conducting a simulation study to identify performance impacts of scaling Tor.

cs.NI↗

arXiv2022

Optimization-Based Predictive Congestion Control for the Tor Network: Opportunities and Challenges

Based on the principle of onion routing, the Tor network achieves anonymity for its users by relaying user data over a series of intermediate relays. This approach makes congestion control in the network a challenging task. As of today, this results in higher latencies due to considerable backlog as well as unfair data rate allocation. In this paper, we present a concept study of PredicTor, a novel approach to congestion control that tackles clogged overlay networks. Unlike traditional approaches, it is built upon the idea of distributed model predictive control, a recent advancement from the area of control theory. PredicTor is tailored to minimizing latency in the network and achieving max-min fairness. We contribute a thorough evaluation of its behavior in both toy scenarios to assess the optimizer and complex networks to assess its potential. For this, we conduct large-scale simulation studies and compare PredicTor to existing congestion control mechanisms in Tor. We show that PredicTor is highly effective in reducing latency and realizing fair rate allocations. In addition, we strive to bring the ideas of modern control theory to the networking community, enabling the development of improved, future congestion control. We therefore demonstrate benefits and issues alike with this novel research direction.

cs.NI↗

arXiv2021

Operating Tor Relays at Universities: Experiences and Considerations

In today's digital society, the Tor network has become an indispensable tool for individuals to protect their privacy on the Internet. Operated by volunteers, relay servers constitute the core component of Tor and are used to geographically escape surveillance. It is therefore essential to have a large, yet diverse set of relays. In this work, we analyze the contribution of educational institutions to the Tor network and report on our experience of operating exit relays at a university. Taking Germany as an example (but arguing that the global situation is similar), we carry out a quantitative study and find that universities contribute negligible amounts of relays and bandwidth. Since many universities all over the world have excellent conditions that render them perfect places to host Tor (exit) relays, we encourage other interested people and institutions to join. To this end, we discuss and resolve common concerns and provide lessons learned.

cs.NI↗

arXiv2020

PredicTor: Predictive Congestion Control for the Tor Network

In the Tor network, anonymity is achieved through a multi-layered architecture, which comes at the cost of a complex network. Scheduling data in this network is a challenging task and the current approach shows to be incapable of avoiding network congestion and allocating fair data rates. We propose PredicTor, a distributed model predictive control approach, to tackle these challenges. PredicTor is designed to schedule incoming and outgoing data rates on individual nodes of the Tor architecture, leading to a scalable approach. We successfully avoid congestion through exchanging information of predicted behavior with adjacent nodes. Furthermore, we formulate PredicTor with a focus on fair allocation of resources, for which we present and proof a novel optimization-based fairness approach. Our proposed controller is evaluated with the popular network simulator ns-3, where we compare it with the current Tor scheduler as well as with another recently proposed enhancement. PredicTor shows significant improvements over the previous approaches, especially with respect to latency.

cs.NI↗