Transport Layer Security (TLS)

Transport Layer Security encrypts application sessions above the transport layer, most visibly as the S in HTTPS. The handshake does the clever part: the client validates the server’s certificate, then the two sides use asymmetric encryption (a key exchange such as ephemeral Diffie-Hellman) to agree fresh session keys. Bulk traffic is then protected with symmetric encryption, which is orders of magnitude faster, so the asymmetric work happens once per session and symmetric ciphers carry the data.

SSL is the deprecated predecessor, and the distinction is deliberate exam bait: every SSL version is broken and prohibited, so the correct term and the correct choice is always TLS (1.2 or 1.3), whatever the marketing phrase “SSL certificate” suggests. Trust rests on the certificate chain up to a root CA, which is why a compromised or rogue CA undermines TLS wholesale; certificate pinning hardens high-value clients against exactly that by accepting only a known certificate or key.

Exam relevance: if a scenario mentions HTTPS, a handshake, or protecting one application’s session in transit, the answer is TLS, and any option naming SSL is a distractor. Contrast IPsec, which secures all IP traffic at the network layer regardless of application; TLS protects a single session between one client and one service.