SSL / TLS

TLS is often called SSL, although both protocols encrypts traffic between clients and servers and proves the server's identity with certificates, SSL is just the predecessor of TLS, which is more modern and secure. Expired certs, hostname mismatches, broken chains, and failed renewals cause some of the most visible production outages. openssl is the essential tool for inspecting handshakes, validating chains, and debugging certificate problems.

As of today, the industry has completely upgraded from SSL to TLS, however, certificates and other TLS products are still referred to as "SSL" due to historical habit.