Measuring and Mitigating AS-level Adversaries Against Tor.

Rishab Nithyanand, Oleksii Starov, Phillipa Gill, Adva Zair, Michael Schapira

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


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 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 under 3% 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 low-capacity relays.
Original languageEnglish
Title of host publicationNetwork and Distributed Systems Security (NDSS) Symposium 2016
Number of pages15
ISBN (Electronic)1-891562-41-X
StatePublished - 2016
EventNetwork and Distributed System Security (NDSS) Symposium 2016 - Catamaran Resort Hotel & Spa, San Diego, United States
Duration: 21 Feb 201624 Feb 2016


ConferenceNetwork and Distributed System Security (NDSS) Symposium 2016
Country/TerritoryUnited States
CitySan Diego
Internet address


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