If you want to discover what crypto is I recommend you take a look at The Matasano Crypto Challenges.
These free exercises are very very very interesting. Some are "easy" and some are really challenging. They cover many subjects and you'll learn a lot. Some of the described attacks made me think about the security of my websites. I changed a few things to prevent crypto attacks.
What I love is the wording of the exercises. They give you just enough information to do them. They make you think. You really have to understand what you are doing. You won't find the solutions on search engines ;-)
I've done 46 of the current 48 exercises. I am still scratching my head on #47. Good luck to you!