Cryptography II by Dan Boneh
It looks like the people at Coursera have added several more free online-courses that you can take. I'm in one of these right now, the class on quantum computing. It definitely seems to be off to a good start, although I wonder how many other students have the necessary background in linear algebra for it. If the linear algebra is easy for you, this particular class seems to be fairly straightforward, but if you're weak in that area it might end up being fairly inaccessible.
In any event, Cryptography II, which will be taught by Dan Boneh, was just added to the list of upcoming courses. The next session starts on January 21, 2013 and runs for six weeks. I've heard that the Crypto I class was very good, and it seems reasonable to assume that the sequel will be just as good.
Here's a description of this class and what it will cover:
Cryptography is an indispensable tool for protecting information in computer systems. This course is a continuation of Crypto I and explains the inner workings of public-key systems and cryptographic protocols. Students will learn how to reason about the security of cryptographic constructions and how to apply this knowledge to real-world applications. The course begins with constructions for digital signatures and their applications. We will then discuss protocols for user authentication and zero-knowledge protocols. Next we will turn to privacy applications of cryptography supporting anonymous credentials and private database lookup. We will conclude with more advanced topics including multi-party computation and elliptic curve cryptography. Throughout the course students will be exposed to many exciting open problems in the field. The course will include written homeworks and optional programming labs. The material is self-contained, but the course assumes knowledge of the topics covered in Crypto I as well as a basic understanding of discrete probability theory.