What are good sources for properly learning cryptography for a mathematician? I'm a pure mathematics student(currently in a Msc program) looking to get into cryptography. I imagine most "regular" introductory books on cryptography would avoid being too heavy on mathematical details due to the target audience. So I'd like to ask, if someone is perhaps able to recommend good books that provide an introduction to cryptography for someone rather unfamiliar with it, but having all the neccessary mathematical background to understand full details and justifications of the algorithms etc. 

Edit: I'm aware that I can't possibly know  every theorem etc. involved, but I think it's safe to assume that I should be able to lookup any such additional details in reasonable time, while going through the book.
Reference requests are off-topic here, so your question will likely be closed. Nevertheless, here are three pretty good introductory books that don't skimp on mathematical details. They're all intended for grad students with a good amount of mathematical maturity. 


Foundations of Cryptography volume 1, by Goldreich. This is the classic book in what I sometimes think of as "complexity-theoretic crypto", which starts with one-way functions (OWFs) and builds more complex primitives like pseudorandom generators and zero-knowledge proofs from OWFs. Another (soon-to-be-published) book of this type is Pass and shelat's "A Course in Cryptography"; you can google around for the most recent version.
Introduction to Modern Cryptography by Katz and Lindell. This is a newer book that covers what most people consider "applied cryptography" - that is, how do you build an encryption scheme that you would really implement to protect some data. Books in this genre generally start with the one-time pad instead of OWFs. Covers the basics of symmetric- and public-key cryptography well, but does not cover zero-knowledge proofs.
A Graduate Course in Applied Cryptography, by Boneh and Shoup. A draft of a not-yet-complete book on applied cryptography. The finished chapters cover a fairly large subset of what Katz/Lindell does, and some subjects (e.g. constructing PRFs) in more detail. Also has a lot of nice exercises and neat "case studies" on topics like side channels.


Because someone suggested it in a comment: I would avoid more specialty texts that only cover the mathematics of public-key crypto, at least for your first text. This includes Hoffstein et al.'s "...mathematical cryptography" and Koblitz's books. These are good books, but they'll only teach you enough modern cryptography (i.e. security reductions and definitions) to be dangerous. Learn how to do a proof by reduction and understand security definitions before you get into the deep mathematics of public-key cryptography.