The Stanford cryptography class (http://crypto.stanford.edu/~dabo/cs255/) and associated book (https://crypto.stanford.edu/~dabo/cryptobook/BonehShoup_0_4....) is almost everything you'd ever want to know about cryptography. If you really like that and want to see the frontiers of cryptography research, the next (and last!) class is https://crypto.stanford.edu/cs355/23sp/; alternatively, there's a security class (https://cs155.stanford.edu/) more focused on industry and application.

Pro tip: nearly every instance of both these classes is available online (all the way back to 1998!), so if something's not making sense, you can always go back and see if it was explained differently in a prior iteration of the class.