Academics discover hidden HTTPS SNI filtering system in China's Great Firewall

I wish browser vendors would collectively pick some date in the future to make eSNI/ECH mandatory for HTTPS connections. Force China to either block the entire West, or not block anything at all.

This explanation of this as a "second system" in the form of a "backup middlebox" feels extremely strange, as the behavior described--particularly how the "two" mechanisms are contingent: if the "primary" happens the "backup" does not (which the authors keep noting and seem to think is very surprising, due to their assertion that this is two otherwise separate middleboxes)--makes it feel like this is much more likely to be a single middlebox doing some stateful flow analysis that bails after deciding to kill a connection.

During the TLS handshake, is the server's TLS certificate sent encrypted? If sent in plaintext, it seems to me, the GFW could easily block connections based on the certificate, even if eSNI is used.

Based on this [1] description of the handshake, the DH random values are exchanged before the certs, so they could in principle encrypt the certs. But it doesn't say if this is actually been done.

[1] https://docs.microsoft.com/en-us/windows/win32/secauthn/tls-...