Security News > 2020 > August > China now blocking ESNI-enabled TLS 1.3 connections, say Great-Firewall-watchers

China is now blocking encrypted HTTPS traffic that uses TLS 1.3 with ESNI enabled, according to observers at the Great Firewall Report.

While TLS hides the content of a user's communication, it cannot always hide the server they are communicating with because its handshake optionally contains a Server Name Indication field designed to explain where traffic is going.

To address that privacy gap, TLS introduced Encrypted SNI. ENSI encrypts the SNI so that intermediaries cannot view it and thus, in theory at least, prevent overzealous censors from sniffing and blocking traffic headed to and from places they don't like.

According to the GFR, China has found one way around this: outright block all TLS 1.3 connections with ESNI enabled.

The GFR team also found that any time an ESNI connection was black-holed, any connection with the same tuple triple of source IP, destination, and destination port would continue to be blocked for up to 180 seconds.

News URL

https://go.theregister.com/feed/www.theregister.com/2020/08/11/china_blocking_tls_1_3_esni/