TLS is the most important and widely-used protocol for secure and encrypted communication, e.g. HTTPS. It offers more than just encryption. TLS also ensures data integrity and strong authentication with X.509 certificates. Did you ever wonder how TLS and CAs actually work? I'll give you the rundown of the basic cryptographic building blocks, protocol handshake, inner structure of certificates, PKI, and what's new in TLS 1.3.