Glossary / TLS

What is TLS

TLS (Transport Layer Security) is the protocol that encrypts data between a browser and a server so it cannot be read or tampered with in transit. It is what puts the S in https and the padlock in the browser. TLS replaced the older SSL protocol, though people still say SSL out of habit.

When a browser connects to a site, the two run a handshake: they agree on a TLS version, exchange keys, and verify the server's certificate. After that all traffic is encrypted, and anyone in between sees only a meaningless stream of bytes.

The current versions are TLS 1.2 and TLS 1.3. The older TLS 1.0 and 1.1, along with all of SSL, are considered unsafe and modern browsers reject them. TLS 1.3 is faster because it shortens the handshake and drops outdated algorithms.

TLS does not only protect websites. The same protocol secures email, messengers, APIs, and other connections. For a regular site owner, though, what matters is a fresh certificate and modern TLS versions enabled on the server.

Example

TLS 1.3, cipher TLS_AES_128_GCM_SHA256

Common mistakes

• Treating SSL and TLS as different technologies. TLS is just the newer name for the same protection, SSL is long obsolete.
• Leaving old TLS 1.0/1.1 enabled for compatibility, which reopens known vulnerabilities.
• Thinking TLS hides which site you visit. The domain is visible, only the content is encrypted.

Related terms

• SSL certificate What is an SSL certificate
• HTTPS What is HTTPS
• wildcard certificate What is a wildcard certificate
• Let's Encrypt What is Let's Encrypt
• certificate chain What is a certificate chain