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Institute
Users of an onion routing network, such as Tor, depend on its anonymity properties. However, especially malicious entry nodes, which know the client’s identity, can also observe the whole communication on their link to the client and, thus, conduct several de-anonymization attacks. To limit this exposure and to impede corresponding attacks, we propose to multipath traffic between the client and the middle node to reduce the information an attacker can obtain at a single vantage point. To facilitate the deployment, only clients and selected middle nodes need to implement our approach, which works transparently for the remaining legacy nodes. Furthermore, we let clients control the splitting strategy to prevent any external manipulation.
Security and Performance Implications of BGP Rerouting-resistant Guard Selection Algorithms for Tor
(2020)
Website fingerprinting (WFP) aims to infer information about the
content of encrypted and anonymized connections by observing
patterns of data flows based on the size and direction of packets. By
collecting traffic traces at a malicious Tor entry node — one of the
weakest adversaries in the attacker model of Tor — a passive eavesdropper can leverage the captured meta-data to reveal the websites visited by a Tor user. As recently shown, WFP is significantly more effective and realistic than assumed. Concurrently, former WFP defenses are either infeasible for deployment in real-world settings or defend against specific WFP attacks only.
To limit the exposure of Tor users to WFP, we propose novel
lightweight WFP defenses, TrafficSliver, which successfully counter
today’s WFP classifiers with reasonable bandwidth and latency
overheads and, thus, make them attractive candidates for adoption
in Tor. Through user-controlled splitting of traffic over multiple
Tor entry nodes, TrafficSliver limits the data a single entry node
can observe and distorts repeatable traffic patterns exploited by
WFP attacks.We first propose a network-layer defense, in which we
apply the concept of multipathing entirely within the Tor network.
We show that our network-layer defense reduces the accuracy from
more than 98% to less than 16% for all state-of-the-art WFP attacks
without adding any artificial delays or dummy traffic. We further
suggest an elegant client-side application-layer defense, which is
independent of the underlying anonymization network. By sending
single HTTP requests for different web objects over distinct Tor
entry nodes, our application-layer defense reduces the detection
rate of WFP classifiers by almost 50 percentage points. Although it
offers lower protection than our network-layer defense, it provides
a security boost at the cost of a very low implementation overhead and is fully compatible with today's Tor network.
Out-of-the-box Multipath TCP as a Tor Transport Protocol: Performance and Privacy Implications
(2020)
Node discovery is a fundamental service for any overlay network, including anonymization networks. Although anonymization and node discovery are two disjoint services, the node discovery has a direct impact on the anonymization. Centralized methods require a trusted third party, limit the network scalability, and are vulnerable to intersection (statistical disclosure) attacks. Therefore, several distributed node discovery methods were proposed to meet the security requirements of anonymization networks through additional structures within Distributed Hash Tables (DHTs). However, they require a high management overhead, a strict cooperation between nodes, and are susceptible to active and passive attacks.We propose WhisperChord—an alternative distributed node discovery approach, which incorporates gossiping into structured overlays. WhisperChord is based on a Chord DHT and neither creates any additional structures within the DHT nor requires any trusted third party. Via simulations, we show that our method provides superior protection against active attacks than prior methods and can effectively thwart information leakages.