This chapter serves to form an intuition about security protocols and their security properties, without requiring formal understanding. Two case studies are presented. The first case study develops an ePassport protocol by starting with a simple protocol that is not secure and iteratively improving it such that successively stronger secrecy and authentication properties are satisfied. Exercises provide an introductory hands-on tutorial, giving an early taste of using tools to verify those security protocols. The second case study examines compelling authentication vulnerabilities in the EMV protocol used for making payments.