Position: Postdoctoral Fellow 

Current Institution: Princeton University


Position: Postdoctoral Research Associate

Studying the Great Firewall of China: From Internet Filtering to Actively Probing Anti-Censorship Tools

Almost 20 years ago, the Chinese government initiated legislation to regulate the Internet in Mainland China, resulting in the birth of a national firewall known as the Great Firewall of China (GFW). In the past couple of years, the operational development of the GFW has significantly escalated state-level information control. To enforce censorship policies, the Chinese government has augmented the GFW with sophisticated techniques that not only discover and block, but also actively attack anti-censorship tools. In this presentation, I will give a detailed overview of my research on this topic. First, I present how the Chinese government used its “Great Cannon” to attack CloudFlare and GitHub because they hosted mirrors of Greatfire.org (a website that distributes information about GFW censorship and circumvention). Then, I will describe how my co-authors and I used new side channel techniques to investigate the GFW over time and space. These side-channel techniques scale well, allowing us to answer questions that were previously out of reach. At the same time, the techniques are designed with ethical considerations in mind: they do not require active participation by clients behind the GFW and thus avoid exposing activists to legal reprisals by the Chinese government. Finally, I will paint a detailed picture of the GFW’s active probing system, which is deployed to detect and block hidden circumvention tools. I will show that the system makes use of a large number of IP addresses, provide evidence that all these IP addresses are centrally controlled, and determine the location of the Great Firewall’s sensors.

Roya Ensafi is a Postdoctoral Research Associate in Computer Science Department and a research fellow at the Center for Information Technology Policy (CITP) at Princeton University. Her research work focuses on computer networking and security, with an emphasis on network measurement. The primary goal of her current research is to better understand and bring transparency to network interference (e.g. censorship) by designing new tools and techniques. In her dissertation, which passed with distinction, Roya developed side channels to remotely measure TCP connectivity between two hosts, without requiring access to any of the hosts. Most of her latest research projects center around studying national firewalls, especially the Great Firewall of China (GFW). Her work studying how the Great Firewall of China discovers hidden circumvention servers received an IRTF Applied Networking Research Prize (ANRP) in 2016. Her work has been published in the USENIX Security Symposium, the ACM Internet Measurement Conference, and the Symposium on Privacy Enhancing Technologies. While a Ph.D. student at the University of New Mexico, she received the Sigma Xi Research Excellence and the UNM Best Graduate Student Mentor awards.