Researchers in Sweden have found out that the Chinese government has updated the “Great Firewall” making it harder for citizens to use the Tor network for surfing the Internet anonymously. The government has been blocking access to some IP addresses or using the HTTP header filters to block traffic.
Philipp Winter and Stefan Lindskog of Karlstad University discovered that the Chinese government recently increased the filtering tools by blocking Tor bridges. Tor bridges are the entry points to the Tor network. The two researchers have found out how the blocking is being done and have suggested ways to get around it. The firewall searches Internet traffic that indicate a network connection as a Tor and initiates a scan of the host. The scan attempts to “speak Tor” to the host and if the interaction is successful, the bridge is blocked.
“The scanners are mostly random IP addresses originating from address pools of ISPs. Therefore it is very hard for a bridge to differentiate between a legitimate user from China and a scanner,” said Winter in an interview with V3.
Some of the tools that helps get around the Great Firewall include obfsproxy. It makes the connection appear to be Skype traffic. “Unfortunately, China is blocking the few publicly available obfsproxy bridges at the moment but non-public obfsproxy bridges work,” added Winter.