China briefly blocked nearly all encrypted internet traffic in the early hours of Aug. 20, in what cybersecurity researchers and engineers believe was a large-scale test of an upgraded version of the country’s internet censorship system, known as the Great Firewall.
From 12:34 a.m. to 1:48 a.m. Beijing time on Aug. 20, China’s internet filtering system injected forged reset signals into all connections using TCP port 443—the standard port for HTTPS traffic. It caused widespread connectivity failures between users in China and overseas websites, according to a technical analysis by the Great Firewall Report, a foreign research group that monitors Chinese internet censorship.
