How to Disable the Google Chrome ‘TLS 1.3 Early Data’ Flag

The Zero Round Trip Time Protocol

Transport Layer Security (TLS) is the cryptographic protocol that secures HTTPS connections on the web. Historically, establishing a secure TLS connection required multiple “round trips” of data between your browser and the server to negotiate the encryption keys before any actual website data could be sent. TLS 1.3 introduced a highly experimental feature known as “Early Data” (or 0-RTT, Zero Round Trip Time). This feature allows Chrome to remember the encryption keys from a previous visit to a website and immediately send encrypted HTTP requests on the very first packet of a new connection, theoretically speeding up page load times slightly.

While performance improvements are always welcome, 0-RTT carries a specific security vulnerability known as a “replay attack.” Because the first packet of data is sent before the server can fully guarantee the freshness of the connection, a malicious actor on the network could theoretically intercept that initial packet (which might contain a login request or a database modifying command) and “replay” it to the server multiple times. While servers are supposed to implement mitigations against this, many do not. If you prioritize absolute cryptographic security over saving a few milliseconds of connection time, you should disable this experimental TLS feature.

How to Turn Off TLS 1.3 Early Data

You can force Chrome to use standard, secure TLS handshakes via the experimental flags menu.

1. Open Google Chrome.
2. Click inside the main address bar at the top of the browser window.
3. Type chrome://flags and press Enter.
4. On the “Experiments” page, use the search bar to look for TLS 1.3 Early Data.
5. The specific flag controlling 0-RTT will be highlighted in yellow. Click the dropdown menu next to it.
6. Change the setting from “Default” to Disabled.
7. Click the blue Relaunch button at the bottom of the screen.

Upon restarting, Chrome will always perform a full, mathematically verified TLS handshake before sending any HTTP requests, protecting you against potential replay attacks on vulnerable servers.