CS255 Intro to Cryptography was one of my favorite courses as a Stanford student. Dan is an incredible instructor. If you want more Stanford security course material, I also recommend CS253 Web Security (https://web.stanford.edu/class/cs253/) (disclosure: I created this course) and CS356 Topics in Computer and Network Security (https://cs356.stanford.edu/).
Seconding this - I loved 155, 255, and 251 from Professor Boneh. He's very talented and was one of my favorite instructors for multiple years; great at explaining concepts.
Videos for CS253 are online here: https://www.youtube.com/playlist?list=PL1y1iaEtjSYiiSGVlL1cH...