Following on from Part 3 , Eric Lippert has posted Part 4 of his series of posts on Hashing and security he also discusses Keberos...If you're really into this sort of stuff but not from an overly mathematical background (like me) the best book I've found on Cryptography is Practical Cryptography by Niels Ferguson and Bruce Schnier this covers pretty much everything the non-NSA employee could need to know about this topic.