What is TLS?
The cryptographic protocol that encrypts and authenticates network traffic, the security layer under HTTPS, SMTPS, and most modern protocols.
TLS (Transport Layer Security) provides three guarantees: confidentiality (no third party can read the traffic), integrity (no third party can modify it without detection), and authentication (the client knows it's really talking to the named server, via the certificate chain).
A TLS handshake negotiates a cipher suite, exchanges certificates, and derives a session key, all in 1-2 round trips for TLS 1.3. After that, every byte of application data is encrypted with a symmetric cipher (typically AES-GCM or ChaCha20-Poly1305) until the session ends.
TLS 1.3 (2018) was a substantial cleanup over 1.2: fewer round trips, simpler cipher suite choices, mandatory forward secrecy, and the removal of many known-weak primitives. As of 2026 TLS 1.3 is the default in every major browser and server stack.