What are the best practices for configuring TLS false start in Chrome?

1 What is TLS false start and how does it work?

TLS, or Transport Layer Security, is a protocol that encrypts and authenticates the communication between a browser and a server. It consists of two phases: the handshake and the data exchange. The handshake is where the browser and the server agree on the encryption parameters, such as the cipher suite, the key exchange method, and the certificates. The data exchange is where the browser and the server send and receive the actual application data, such as web pages, images, or scripts.

TLS false start is a feature that allows the browser to skip the last round trip of the handshake and start sending application data right after it receives the server's finished message. This can save up to 30% of the time needed to establish a secure connection, especially for short-lived or latency-sensitive requests. However, it also means that the browser does not wait for the server to verify its finished message, which could expose it to some attacks, such as renegotiation or truncation.

2 How to enable or disable TLS false start in Chrome?

Chrome supports TLS false start by default, but it also provides some options to enable or disable it manually. You can use the following flags to control the behavior of TLS false start in Chrome:

-

--enable-tls13-early-data        

: This flag enables TLS false start for TLS 1.3 connections, which use a new mechanism called early data to send application data before the handshake is completed. This flag is enabled by default in Chrome 86 and later.

-

--ssl-false-start        

: This flag enables TLS false start for TLS 1.2 and lower connections, which use the standard TLS false start feature. This flag is enabled by default in Chrome, but it may be disabled by some enterprise policies or extensions.

-

--disable-ssl-false-start        

: This flag disables TLS false start for all connections, regardless of the TLS version. This flag may be useful for debugging or testing purposes, or for users who prefer to sacrifice some performance for more security.

You can add these flags to the Chrome shortcut or command line, or use the chrome://flags page to access them.

3 What are the benefits and drawbacks of TLS false start in Chrome?

TLS false start in Chrome can offer some benefits and drawbacks, depending on the context and the scenario. Faster page load times, improved user experience, and more efficient resource utilization are some of the advantages of TLS false start. However, compatibility issues, security trade-offs, and privacy concerns may arise as well. TLS false start can reduce the time needed to establish a secure connection by one round trip, which can translate into faster page load times for websites that use HTTPS or HSTS. Additionally, it can make web pages more interactive and responsive. Furthermore, it can reduce the network overhead and CPU usage by sending application data earlier and avoiding unnecessary handshakes. On the other hand, TLS false start may not work with some servers or intermediaries that do not support it or expect a full handshake before receiving application data. This could cause connection errors or timeouts. Moreover, it may expose the browser to attacks that exploit the lack of verification of the finished message, such as renegotiation or truncation attacks. Lastly, it may reveal information about the browser or user to the server or an observer before the connection is established, such as user agent, cookies, or requested URL.

4 How to test and troubleshoot TLS false start in Chrome?

If you want to test or troubleshoot TLS false start in Chrome, you can use a variety of tools and methods to monitor and analyze the behavior and performance of your web applications. For instance, Chrome DevTools can be used to inspect network activity and security details, such as the timing and size of requests/responses, TLS version and cipher suite used, as well as certificate and protocol information. Additionally, SSL Labs can be used to evaluate security and compatibility of web servers, revealing supported TLS versions/features, cipher suites/key exchange methods, vulnerabilities/warnings, and how they handle TLS false start/early data. Lastly, Wireshark allows one to capture/analyze network traffic/TLS packets, observing details/contents of each packet, handshake/data exchange phases, flags/messages of each connection; filters/statistics can also be used to focus on aspects or issues of network activity.

5 How to optimize TLS false start in Chrome?

If you want to optimize TLS false start in Chrome, you can follow some best practices and recommendations to enhance the speed and the security of your web applications. TLS 1.3 or higher should be used, as it reduces the number of round trips for the handshake from two to one and introduces features such as early data and forward secrecy. Compatible cipher suites should also be used, such as ECDHE or DHE which generate ephemeral keys for each session, rather than static keys like RSA or PSK. Finally, reliable servers and intermediaries should be used that are compatible with TLS false start and early data, or configured properly to handle them.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?