Encrypted Client Hello
ECH
The fix for HTTPS's last big privacy leak. Even on an encrypted connection, the site name was visible in the opening handshake — ECH encrypts that too, so the network can no longer see which sites you visit.
Encrypted Client Hello (ECH) is a TLS extension that encrypts the very first message of the TLS handshake — the "ClientHello" — including the SNI field that names the website you are connecting to. It closes a surprising gap: for years, even fully encrypted HTTPS connections announced their destination site in plain text at the start, letting any network observer build a list of every domain you visited.
The leak ECH closes
HTTPS encrypts the content of your connection, but the handshake that sets it up had a plain-text problem. The SNI field exists so that one server hosting many sites knows which certificate to present — but because it was unencrypted, it also told your ISP, network, or anyone on the path exactly which site you were loading.
| What an observer sees | Without ECH | With ECH |
|---|---|---|
| Your data / page content | Encrypted | Encrypted |
| The site name (SNI) | Visible in clear text | Encrypted |
| That you connected somewhere | Visible | Visible (destination IP) |
How it works
ECH uses a public key the website publishes (fetched via DNS) to encrypt the sensitive parts of the ClientHello. The connection is addressed to a shared front-end — typically a large CDN — which can decrypt the inner request and route it to the right site, all without the true site name ever appearing on the wire. To an outside observer, many different sites behind the same CDN look identical at the handshake stage.
Why it needs encrypted DNS
ECH depends on fetching the website's ECH keys, and that lookup happens over DNS. If DNS were unencrypted, an observer could still infer the destination from the DNS query — undoing ECH's benefit. So ECH is designed to work hand-in-hand with encrypted DNS like DoH or DoT. Together, encrypted DNS hides the lookup and ECH hides the handshake, removing the two main ways a network learns which sites you browse. Only the destination IP address remains visible — and with large CDNs, one IP serves countless sites.
Availability
ECH is a relatively new and still-deploying standard. It works automatically and invisibly when every piece lines up — your browser supports it, the site and its CDN have enabled it, and you are using encrypted DNS. Where any of those is missing, the connection simply falls back to the old behaviour. There is nothing to configure; as support spreads, more of your browsing gains this protection silently. It is the natural next step after HTTPS and encrypted DNS in the long march to make where you go online as private as what you do there.