Cryptography is part of my work, a part time hobby, and (with my current reading list) something I do during my free time. So let me pass along some of my wonder.
I found a spectacular NOVA article on Enigma . Specifically how it worked. If you are interested in security in general then be sure to check out Cryptome. Its technical articles has be kinda “thick” at times but much of its information is useful for other purposes. And, because we all need to improve ourselves one way or another, here is Bred Miller’s Guide to Lock Picking.