Reminds me of my cryptography class in college. Before taking the class I had written a peer to peer encrypted messaging tool for fun and to learn about encryption. It had its own handshake, custom RSA, AES, ephemeral messages, tooling to discover peers...

Anyway in the last year of my CS degree I had a class on encryption, got barely a passing grade on the exam. One of the questions I remember was "What color is the lock in the address bar of Google Chrome that indicates a website is encrypted?", there were a bunch of others like that.