CITP Luncheon Speaker Series:
Roya Ensafi – The Great Firewall of China:
From Internet Filtering to Actively Attacking Anti-censorship Tools

CITP Luncheon Series

Date: Tuesday, December 1, 2015
Location: 306 Sherrerd Hall
This talk will not be livestreamed or videotaped.

Food and discussion begin at 12:30 pm. Open to current Princeton faculty, staff, and students. Open to members of the public by invitation only. Please contact Laura Cummings-Abdo at if you are interested in attending a particular lunch.

Almost 20 years ago, the Chinese government initiated legislations to regulate the Internet in Mainland China resulting in the birth of a national firewall known as Great Firewall of China (GFW). The GFW’s main goal is to monitor incoming and outgoing traffic, and disrupt prohibited connections. In the past couple of years, the operational development of the GFW has significantly escalated state-level information control; in order to efficiently enforce their censorship policies, the GFW developed and implemented sophisticated techniques to actively attack anti-censorship tools. In this talk, Ensafi will explain her latest work on detecting and documenting two offensive systems used by the GFW: the GFWs active probing system and the Great Cannon. The GFW’s active probing system is responsible for passively monitoring the network for suspicious traffic, then actively probing the corresponding servers, and blocking any that are determined to run circumvention servers such as Tor. The Great Cannon is another offensive system that is used to launch distributed denial-of-service attacks on websites by intercepting massive amounts of web traffic and redirecting them to targeted websites. After covering these offensive systems, Ensafi will discuss the policy implications raised by their use, including the potential imposition on any user whose browser might visit (even inadvertently) any Chinese web site.


Roya Ensafi is currently a Postdoctoral researcher at Princeton University, working closely with Nick Feamster. Her main research interests lie in the areas of computer networking and network measurement. The primary goal of her current research is to better understand and bring transparency to network interference caused by middleboxes. Most of her latest research projects center around studying national firewalls, especially the Great Firewall of China (GFW). In collaboration with others, she documented two offensive systems used by GFW: the Great Cannon and the GFWs active probing systems. Her work has been published in USENIX Security, PETS, and ACM IMC. Her dissertation measured network interference remotely using side channels and passed with distinction. She received the University of New Mexico Sigma Xi research Excellence award as well as the UNM Best Graduate Student Mentor award of 2014.