Here. I'll start you on better class on cryptography than any video, pdf, or slide deck you're going to find.
Go to this repository, grab the code, and figure out how you can attack it: https://github.com/jackjack-jj/jeeq (of course, along the way go learn whatever you need to). There are several interesting weaknesses in this code, and yet it's not just a toy: it was briefly deployed in a widely used application.
(If you google for it, you might find some of my analysis on it, which would potentially spoil the learning experience, so I suggest you don't. Though if you finish with this one I can dig up some other weak cryptosystems.)
Go to this repository, grab the code, and figure out how you can attack it: https://github.com/jackjack-jj/jeeq (of course, along the way go learn whatever you need to). There are several interesting weaknesses in this code, and yet it's not just a toy: it was briefly deployed in a widely used application.
(If you google for it, you might find some of my analysis on it, which would potentially spoil the learning experience, so I suggest you don't. Though if you finish with this one I can dig up some other weak cryptosystems.)