This tutorial book is a collection of notes and sample codes written by the author while he was learning PKI (Public Key Infrastructure) technologies himself. Topics include Root CA (Certificate Authorities); SSL (Secure Socket Layer), TLS (Transport Layer Security), and HTTPS (HyperText Transfer Protocol Secure) protocols; Server and client authentication processes; Communication data encryption; Using HTTPS with Chrome, Firefox, Edge and Internet Explorer; Managing certificates on Windows, iOS and Android systems; X.509 certificate format; Certificate store and management tools; Certificate validation chain; CSR (Certificate Signing Request); Digital signature on MS Word and OpenOffice documents; Get free personal certificate from Comodo.