Description from the site: We've built a collection of 48 exercises that demonstrate attacks on real-world crypto. 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. http://cryptopals.com/ This is a pretty interesting resource to learn more about crypto.