Yixin Sun will present her Pre FPO, "Enhancing Anonymity Systems under Network and User Dynamics" on April 24, 2019 at 3pm in CS 402. The members of her committee are as follows: Prateek Mittal (reader), Nick Feamster (reader), Mung Chiang (advisor), Jennifer Rexford (non-reader), Ed Felten (non-reader) Everyone is invited to attend her talk. The talk title and abstract follow below. Title: Enhancing Anonymity Systems under Network and User Dynamics Abstract: Privacy on the Internet is eroding rapidly. Anonymity systems have been designed to protect the identity and privacy of users from untrusted destinations and third parties on the Internet. However, many anonymity systems assume that important system components, such as the network infrastructure and client location, are static. In practice, these components are highly dynamic and exhibit changes over time. In this dissertation, I exploit network and user dynamics to uncover new attacks in anonymity systems, and consequently build defenses to protect user anonymity from such new attacks. First, we present Raptor attacks, that can be launched by Autonomous Systems (ASes) to compromise user anonymity in the Tor network. AS-level adversaries can exploit the asymmetric nature of Internet routing and launch active routing attacks to observe user traffic and deanonymize users via traffic correlation analysis. We successfully demonstrate the attacks in the wild with 95% accuracy rate. Second, we design the Counter-Raptor defense to safeguard Tor against active routing attacks via a new Tor guard relay selection algorithm that incorporates the resilience of relays into consideration. We show that the algorithm successfully improves the security for Tor clients by up to 36% on average (up to 166% for certain clients). Finally, we present Tempest attack that exploits client mobility to compromise anonymity. Using experimental analysis on real-world datasets, we demonstrate that mobility degrades user privacy across a wide range of anonymity systems, including deployed systems such as Tor; path-selection protocols for Tor such as DeNASA and Counter-RAPTOR; and network-layer anonymity protocols for Internet routing such as HORNET.