1,649 research outputs found
Defending Tor from Network Adversaries: A Case Study of Network Path Prediction
The Tor anonymity network has been shown vulnerable to traffic analysis
attacks by autonomous systems and Internet exchanges, which can observe
different overlay hops belonging to the same circuit. We aim to determine
whether network path prediction techniques provide an accurate picture of the
threat from such adversaries, and whether they can be used to avoid this
threat. We perform a measurement study by running traceroutes from Tor relays
to destinations around the Internet. We use the data to evaluate the accuracy
of the autonomous systems and Internet exchanges that are predicted to appear
on the path using state-of-the-art path inference techniques; we also consider
the impact that prediction errors have on Tor security, and whether it is
possible to produce a useful overestimate that does not miss important threats.
Finally, we evaluate the possibility of using these predictions to actively
avoid AS and IX adversaries and the challenges this creates for the design of
Tor
Representing Network Trust and Using It to Improve Anonymous Communication
Motivated by the effectiveness of correlation attacks against Tor, the
censorship arms race, and observations of malicious relays in Tor, we propose
that Tor users capture their trust in network elements using probability
distributions over the sets of elements observed by network adversaries. We
present a modular system that allows users to efficiently and conveniently
create such distributions and use them to improve their security. The major
components of this system are (i) an ontology of network-element types that
represents the main threats to and vulnerabilities of anonymous communication
over Tor, (ii) a formal language that allows users to naturally express trust
beliefs about network elements, and (iii) a conversion procedure that takes the
ontology, public information about the network, and user beliefs written in the
trust language and produce a Bayesian Belief Network that represents the
probability distribution in a way that is concise and easily sampleable. We
also present preliminary experimental results that show the distribution
produced by our system can improve security when employed by users; further
improvement is seen when the system is employed by both users and services.Comment: 24 pages; talk to be presented at HotPETs 201
Measuring and mitigating AS-level adversaries against Tor
The popularity of Tor as an anonymity system has made it a popular target for
a variety of attacks. We focus on traffic correlation attacks, which are no
longer solely in the realm of academic research with recent revelations about
the NSA and GCHQ actively working to implement them in practice.
Our first contribution is an empirical study that allows us to gain a high
fidelity snapshot of the threat of traffic correlation attacks in the wild. We
find that up to 40% of all circuits created by Tor are vulnerable to attacks by
traffic correlation from Autonomous System (AS)-level adversaries, 42% from
colluding AS-level adversaries, and 85% from state-level adversaries. In
addition, we find that in some regions (notably, China and Iran) there exist
many cases where over 95% of all possible circuits are vulnerable to
correlation attacks, emphasizing the need for AS-aware relay-selection.
To mitigate the threat of such attacks, we build Astoria--an AS-aware Tor
client. Astoria leverages recent developments in network measurement to perform
path-prediction and intelligent relay selection. Astoria reduces the number of
vulnerable circuits to 2% against AS-level adversaries, under 5% against
colluding AS-level adversaries, and 25% against state-level adversaries. In
addition, Astoria load balances across the Tor network so as to not overload
any set of relays.Comment: Appearing at NDSS 201
Dovetail: Stronger Anonymity in Next-Generation Internet Routing
Current low-latency anonymity systems use complex overlay networks to conceal
a user's IP address, introducing significant latency and network efficiency
penalties compared to normal Internet usage. Rather than obfuscating network
identity through higher level protocols, we propose a more direct solution: a
routing protocol that allows communication without exposing network identity,
providing a strong foundation for Internet privacy, while allowing identity to
be defined in those higher level protocols where it adds value.
Given current research initiatives advocating "clean slate" Internet designs,
an opportunity exists to design an internetwork layer routing protocol that
decouples identity from network location and thereby simplifies the anonymity
problem. Recently, Hsiao et al. proposed such a protocol (LAP), but it does not
protect the user against a local eavesdropper or an untrusted ISP, which will
not be acceptable for many users. Thus, we propose Dovetail, a next-generation
Internet routing protocol that provides anonymity against an active attacker
located at any single point within the network, including the user's ISP. A
major design challenge is to provide this protection without including an
application-layer proxy in data transmission. We address this challenge in path
construction by using a matchmaker node (an end host) to overlap two path
segments at a dovetail node (a router). The dovetail then trims away part of
the path so that data transmission bypasses the matchmaker. Additional design
features include the choice of many different paths through the network and the
joining of path segments without requiring a trusted third party. We develop a
systematic mechanism to measure the topological anonymity of our designs, and
we demonstrate the privacy and efficiency of our proposal by simulation, using
a model of the complete Internet at the AS-level
The Maestro Attack: Orchestrating Malicious Flows with BGP
We present the Maestro Attack, a Link Flooding Attack (LFA) that leverages Border Gateway Protocol (BGP) engineering techniques to improve the flow density of botnet-sourced Distributed Denial of Service (DDoS) on transit links. Specific-prefix routes poisoned for certain Autonomous Systems (ASes) are advertised by a compromised network operator to channel bot-to-bot ows over a target link. Publicly available AS relationship data feeds a greedy heuristic that iteratively builds a poison set of ASes to perform the attack. Given a compromised BGP speaker with advantageous positioning relative to the target link in the Internet topology, an adversary can expect to enhance flow density by more than 30 percent. For a large botnet (e.g., Mirai), the bottom line result is augmenting the DDoS by more than a million additional infected hosts. Interestingly, the size of the adversary-controlled AS plays little role in this effect; attacks on large core links can be effected by small, resource-limited ASes. Link vulnerability is evaluated across several metrics, including BGP betweenness and botnet flow density, and we assess where an adversary must be positioned to execute the attack most successfully. Mitigations are presented for network operators seeking to insulate themselves from this attack
Systematizing Decentralization and Privacy: Lessons from 15 Years of Research and Deployments
Decentralized systems are a subset of distributed systems where multiple
authorities control different components and no authority is fully trusted by
all. This implies that any component in a decentralized system is potentially
adversarial. We revise fifteen years of research on decentralization and
privacy, and provide an overview of key systems, as well as key insights for
designers of future systems. We show that decentralized designs can enhance
privacy, integrity, and availability but also require careful trade-offs in
terms of system complexity, properties provided, and degree of
decentralization. These trade-offs need to be understood and navigated by
designers. We argue that a combination of insights from cryptography,
distributed systems, and mechanism design, aligned with the development of
adequate incentives, are necessary to build scalable and successful
privacy-preserving decentralized systems
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