Reference on cryptography methods I'm looking for a good reference, possibly a survey, on the different types of cryptography methods. As far as I understand, the security of a cryptographic method depends on some hardness assumptions, and I've heard of methods based on the hardness of factorization, discrete logarithm, NP-complete problems (such as the Knapsack problem) and problems on lattices.

Is there any good text addressing the different existing paradigms? 

In particular, I would be interested on open problems and questions on less studied methods.

Answers for this question may include both references to a text giving an overview of the area but also to specific methods.
A good start would be Katz and Lindell's Introduction to Modern Cryptography. 

Alternatively, you might want to take one of the crypto courses on Coursera: I recommend the ones taught by Jonathan Katz and by Dan Boneh (search for "cryptography" on Coursera). They are both free.