Something weird happened with the Great Firewall of China (GFW), which the Chinese government uses to control internet access within the country, on August 20. A site dedicated to monitoring China’s internet censorship systems called GFW Report claimed the Great Firewall “exhibited anomalous behavior by unconditionally injecting forged TCP RST+ACK packets to disrupt all connections on TCP port 443” for approximately 74 minutes before resuming its normal processes. A quick aside: TCP port 443 is typically used for HTTPS — the more Secure version of the Hypertext Transfer Protocol that makes it more difficult for someone to spy on or tamper with the connection between devices — but the port and protocol aren’t inextricably linked. Systems can be configured to manage HTTPS via different ports. The behavior reported by GFW Report differs from China’s previous efforts to censor encrypted communications in that it specifically targeted port 443, with the report saying “the unconditional RST+ACK injections was on TCP port 443, but not on other common ports like 22, 80, 8443.” (Often used for SSH, HTTP, and as an alternative for HTTPS, respectively.)

Full report : China’s Great Firewall blocked all traffic to a common HTTPS port for over an hour, severing connection to the outside world — with no hint as to its intention.