中央研究院 資訊科學研究所

Tor is a free-software anonymizing network that helps people around the world use the Internet in safety. Tor's 1800 volunteer relays carry traffic for several hundred thousand users including ordinary citizens who want protection from identity theft and prying corporations, corporations who want to look at a competitor's website in private, and soldiers and aid workers in the Middle East who need to contact their home servers without fear of physical harm. Tor was originally designed as a civil liberties tool for people in the West. But if governments can block connections to the Tor network, who cares that it provides great anonymity? A few years ago we started adapting Tor to be more robust in countries like China. We streamlined its network communications to look more like ordinary SSL, and we introduced "bridge relays" that are harder for an attacker to find and block than Tor's public relays. In the aftermath of the Iranian elections in June 2009, and then the periodic blockings in China, we've learned a lot about how circumvention tools work in reality for activists in tough situations. I'll give an overview of the Tor architecture, and summarize the variety of people who use it and what security it provides. Then we'll focus on the use of tools like Tor in countries like Iran and China: why anonymity is important for circumvention, why transparency in design and operation is critical for trust, the role of popular media in helping -- and harming -- the effectiveness of the tools, and tradeoffs between usability and security. After describing Tor's strategy for secure circumvention (what we thought would work), I'll talk about how the arms race actually seems to be going in practice