What is Encrypted Client Hello (ECH)?

ECH is a TLSTLS: Transport Layer Security. The encryption that protects most internet traffic, such as HTTPS. extension that encrypts the sensitive part of the ClientHello, including the real server name, with a public key the site publishes in DNS. On the wire, an observer sees only an outer ClientHello carrying a shared public name, typically that of the content-delivery network hosting the site, instead of the actual site. It was designed for privacy: to stop anyone on the path, from a café Wi-Fi to an internet provider, from learning which site you visit. Major browsers support it and some large content-delivery networks offer it, so a share of web traffic already uses it, while most corporate and internal servers do not. ECH usually comes together with encrypted DNS, because otherwise the name would still leak through the DNS query. The certificate and the session content were already encrypted under TLS 1.3; ECH closes one of the last readable fields. For security teams it means fewer names and more reliance on behaviour.

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