Resources

cryptohack,org 

A fun platform for learning modern cryptography by getting your hands dirty while learning about modern cryptographic protocols by solving a series of interactive puzzles and challenges.

This is a different way to learn about crypto than taking a class or reading a book. We give you problems to solve. They're derived from weaknesses in real-world systems and modern cryptographic constructions. We give you enough info to learn about the underlying crypto concepts yourself. When you're finished, you'll not only have learned a good deal about how cryptosystems are built, but you'll also understand how they're attacked.

picoctf.com

Pico CTF is a free learning platform, hosting a wide array of cryptography challenges.