Tools helping China's netizens to bypass the Great Firewall appear to be facing a fresh round of crackdowns in the run-up to the country's quinquennial party congress that will see a top leadership reshuffle. Greater censorship is not at all uncommon during countries' politically sensitive periods, but the stress facing censorship circumvention tools in China appears to be on a whole new level.

"Starting from October 3, 2022 (Beijing Time), more than 100 users reported that at least one of their TLS-based censorship circumvention servers had been blocked," writes GFW Report, a censorship monitoring platform focused on China, in a GitHub post.

TLS, or transport layer security, is a ubiquitous internet security protocol used for encrypting data sent across the internet. Because data shared over a TLS connection is encrypted and cannot be easily read, many censorship circumvention apps and services use TLS to keep people's conversations private. A TLS-based virtual private network, or VPN, directs internet traffic through a TLS connection instead of pushing that traffic to one's internet provider.

But Chinese censors seem to have found a way of compromising this strategy. "The blocking is done by blocking the specific port that the circumvention services listen on. When the user changes the blocked port to a non-blocked port and keeps using the circumvention tools, the entire IP address may get blocked," GFW Report says in the post.

According to GFW Report's estimates provided to TechCrunch, more than half of China's netizens who circumvent online censorship use some sort of TLS-based tools.

Tech-savvy users may buy their own domains and set up services to bypass the so-called "Great Firewall (GFW)", an elaborate censorship system developed by the Chinese authorities to regulate the country's internet access, such as blocking certain foreign web services or slowing down their traffic. But many netizens instead opt for ready-to-use subscription services from resellers, which rely heavily on TLS-based techniques, says GFW Report.