I am a student. I was assigned to the authentication and authorization part of the web service team project, so I wrote the code using the jwt token method. Since I followed someone else's code without understanding it, I searched for various videos to understand it, but I wasted time. This lecture is the answer. It is not important to have a jwt token or a jwt data structure, but the concept of cryptography. (Even if you don't know terms like jwt token or something, if you have a concept of cryptography, you will be able to understand it when you write the code.) The lecture title is "Memorize and finish", but the core concepts are explained very logically. "Memorize and finish" means "I will not prove it mathematically, but I will just organize the results and tell you." Anyway, I gained a lot of knowledge, and it was very fun. Maybe because the lecture title is cryptography, not many people seem to take it, but it is almost essential for developers to know.