Changing of the Guards: A Framework for Understanding and Improving Entry Guard Selection in Tor

Tariq Elahi, Kevin Bauer, Mashael AlSabah, Roger Dingledine, Ian Goldberg

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract / Description of output

Tor is the most popular low-latency anonymity overlay network for the Internet, protecting the privacy of hundreds of thousands of people every day. To ensure a high level of security against certain attacks, Tor currently utilizes special nodes called entry guards as each client's long-term entry point into the anonymity network. While the use of entry guards provides clear and well-studied security benefits, it is unclear how well the current entry guard design achieves its security goals in practice.

We design and implement Changing of the Guards (COGS), a simulation-based research framework to study Tor's entry guard design. Using COGS, we empirically demonstrate that natural, short-term entry guard churn and explicit time-based entry guard rotation contribute to clients using more entry guards than they should, and thus increase the likelihood of profiling attacks. This churn significantly degrades Tor clients' anonymity. To understand the security and performance implications of current and alternative entry guard selection algorithms, we simulate tens of thousands of Tor clients using COGS based on Tor's entry guard selection and rotation algorithms, with real entry guard data collected over the course of eight months from the live Tor network.
Original languageEnglish
Title of host publicationProceedings of the 2012 ACM Workshop on Privacy in the Electronic Society
Place of PublicationNew York, NY, USA
Number of pages12
ISBN (Print)978-1-4503-1663-7
Publication statusPublished - 15 Oct 2012
Event2012 ACM workshop on Privacy in the electronic society - Raleigh, United States
Duration: 15 Oct 201215 Oct 2012

Publication series

NameWPES '12


Conference2012 ACM workshop on Privacy in the electronic society
Abbreviated titleWPES'12
Country/TerritoryUnited States
Internet address

Keywords / Materials (for Non-textual outputs)

  • entry guard, predecessor attack, quality of service, tor


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