Researchers discover first regional internet censorship in China

China's internet censorship is apparently becoming more decentralized: researchers from several US universities have documented for the first time a regional firewall in the Chinese province of Henan that operates independently of the “Great Firewall”. The “Henan Firewall”, which has been active since August 2023, monitors all outgoing internet traffic in the province with a population of 99 million and blocks much more aggressively than the national censorship – with over four million domains blocked at times compared to 741,000 by the Great Firewall.

With over 100 million inhabitants, Henan is one of the most populous provinces in central China. Known primarily as a grain producer, this part of China was the scene of protests in 2022. The demonstrations were directed against the ban on cash withdrawals and escalated when government officials attempted to suppress the protests with the help of pandemic measures.

Systematic tests on rental servers

The discovery of regional censorship began with complaints from internet users in Henan province, who reported in forums from August 2023 that certain websites were suddenly no longer accessible – although they remained accessible in other Chinese provinces. The researchers picked up on this information and rented their servers in Henan to verify the reports. In fact, they found that outgoing Internet traffic from the province was monitored by another censorship system in addition to the national Great Firewall.

To scientifically document the phenomenon, the researchers set up servers in seven Chinese provinces and systematically tested over 10,000 popular websites. In doing so, they discovered the decisive technical signature: while China's Great Firewall blocks connections with empty TCP RST packets, the Henan Firewall sends RST packets with a characteristic 10-byte data attachment. This unique identifier made it possible to distinguish between the two censorship systems and analyze their different blocking strategies.

Changing blocking policies

In a 13-month long-term study, the researchers tested one million domains daily and 227 million domains weekly. This revealed the full extent of regional censorship: the Henan Firewall blocked significantly more than the national Great Firewall. The volatile blocking policy was particularly striking: while the Great Firewall usually blocks websites permanently, in Henan 75 percent of all blocked domains are unblocked after less than 51 days, often by arbitrarily blocking entire country domains such as *.com.au or *.co.za.

Henan may serve as a test area to give local authorities more autonomy in controlling information. It remains unclear whether the use of artificial intelligence also plays a role in the Henan firewall. According to media reports, Chinese censors are toying with the idea of using the technology in the future to be able to block content more quickly and flexibly.

(mki)