The Tor Project is a free network run by volunteers that hides users locations and usage from surveillance and traffic analysis. Essentially, it provides online anonymity to anybody who wants it.
Tor users can send email and instant message, surf websites and post content online without anyone knowing who or where they are. Consequently, it is widely acknowledged as an important tool for freedom of expression.
That's clearly a worry for authoritarian regimes that want to control and limit their citizens' access to the outside world. The biggest and most powerful of these is China and the government there operates a firewall that denies its citizens online access to the outside world.
It's no surprise then that the Great Firewall of China, as it is called, actively blocks access to the Tor network. So an interesting question is how this censorship works and how it might be circumvented.
Today, Philipp Winter and Stefan Lindskog at Karlstad University in Sweden provide an answer.
These guys have conducted a comprehensive analysis of the way the Great Firewall of China blocks Tor and how these measures might be sidestepped.