TLS
Transport Layer Security: handshake, chains, versions, ACME automation (concepts) and diagnostics.
TLS certificate validity reduction — CA/B Forum BR 2.1.6
CA/Browser Forum trajectory on public TLS certificate lifetimes and operational impacts (inventory, renewal).
TLS handshake and session encryption
Protocol negotiation, key exchange, server authentication and protection of the application session.
TLS chains of trust
Leaf certificate, intermediates, trust anchors and common incomplete-chain errors.
Cipher suites and TLS versions
TLS 1.2 / 1.3 comparison, cipher suite selection and disabling obsolete algorithms.
ACME and automatic renewal
ACME protocol, domain validation and renewal automation — general concepts (outside the product).
Common TLS errors and diagnostics
Expired certificate, name mismatch (SAN/CN), missing chain and reading browser or OpenSSL alerts.