Modern Cryptography: Theory and Practice

It's a pretty good one too, but it's still a college text. The orientation of this book is far more theoretical than practical, complete with abstract mathematical notation that sometimes does more to confuse than to elucidate (although the author, to his credit, includes a glossary of mathematical notation early in the text). Still, the book is complete and up-to-date, covering everything from probability theory and number theory through the latest stuff on PKI, symmetric crypto (including AES), and authentication. Cryptography is not an easy subject, and this book will take a while to wade through for all but the most mathematically astute readers. Nonetheless, for those wanting a "deep dive" into the theoretical underpinnings of the subject, this is a good book. Security practitioners will likely find Schneier's "Applied Cryptography" an easier, more enjoyable, and equally beneficial read, although it is due for an update.