I especially liked Part IV, which covers secure electronic commerce because it covered the full spectrum of technologies and the information is immediately useful to all IT and security professionals. Like in the first three parts of this book I came away with a complete understanding of how everything works.
This book epitomizes clear writing. Moreover, it is simply amazing how much knowledge can be relatively painlessly gained from reading this book. Although I am sure the authors intended to make the inner workings of cryptography accessible to non-security professionals (which they unquestionably accomplished), they also set a standard of excellence in technical writing by producing a book that is, in my opinion, near perfect in its ability to seamlessly use lively prose and well thought out illustrations to convey highly technical information. If you need to learn cryptography but are challenged by the math and the impenetratable writing of other books on the subject, start with this one.