Comment by burnt-resistor

Anyone with an undergraduate CS background should be able to handle Dan Boneh's course:

https://www.coursera.org/learn/crypto

Although there are continuums of teaching delivery from muddled to clear explanations of concepts, there are no student shortcuts to escape the irreducible mental exertion to acquire familiarity towards mastery. Uncurious people shouldn't be in the field (no pun intended).