Practical Cryptography [ペーパーバック]

For those of you (including myself) who were expecting an updated version of the Applied Cryptography, this book is NOT it. Based on the pre-publication blurbs here and there, I thought it may be a simple how-to book without too much theory. The book didn't turn out to be that sort of thing either.

This book is, sort of an executive summary of Applied Cryptography (AC), with some updates. It touches upon the insights that Scheneier mentioned in Secret and Lies (like crypto is the easy part and that won't solve security). It mentions some newer material, notably AES related stuff. The description is, in effect, a simplified version of AC. Also, it doesn't try to cover everything, and yes, some explanations about the practical applications are stressed slightly more than in AC.

So if you want to be practical, just go over the essential and latest stuff, this is a good book to read. But I must say that it's not as fun to read as AC. Not as many jokes, and absolutely no crazy stuff (like bio-computing and the significance of dark matters). Oh well, maybe that's what being practical means... But it doesn't give you the feeling of throughness that AC gave. Maybe this comes from my reading AC too much in detail (I actually translated the whole book into Japanese), but I think it is inherent in the book itself. In trying to cover as much ground as possible, the book hurries a lot.

So if you are in a hurry to cover just enough important stuff, get this book. And if you need some explanation on the newer stuff, get this. But I also recommend getting AC as well.

I've read a large number of cryptography books. Very few of them come down to brass tacks. They give you a description of a few algorithms, their strengths and weaknesses, and leave it at that. Either that, or they describe in lovingly complex detail the implementation of a particular protocol, one usually so fraught with options and details that you wonder how, at the end of it, that anybody writes a conforming implementation.

Practical Cryptography does neither of these things. It presents algorithm classes, why they exist, and what the best known algorithms are in each class. It explains how the various strengths and weaknesses of algorithms in each class combine to make a cryptosystem weaker or stronger. Then it goes on to show you how to use that information to build working cryptosystems.

This book is NOT a careful discussion of the implementation details or plusses and minuses of particular algorithms. They give detailed implementation instructions and advice for some algorithms (such as RSA or Diffie-Hellman) that tend to end up being misunderstood or implemented poorly, but the main focus of the book is about putting all the information together to build a real system. This is something that I feel is sorely lacking in the field of cryptography as it stands in 2005 (when I last updated this review).

The book does have a flaw. The authors present several algorithms and techniques that they recently invented and are not 'tried-and-true'. They present good arguments as to why they're secure. But the only real test of such things is lots of peer review and real-world testing. And, since they're new, they haven't been tested in that way.

People have complained about the book's seeming schizophrenia. On one hand, the authors are trying to show you how to build a secure cryptosystem. On the other, they're telling you how hopeless a task it is to build one that has no vulnerabilities, even if you're an expert in such things.

This can be annoying, but I more find it refreshing. Writing a secure cryptosystem is very hard. People should be aware that it is hard, and they are likely to make mistakes. It isn't something that should be attempted lightly. The current state of computer security is depressingly abysmal. People should be encouraged, as much as possible, to not contribute to the problem.

I'm not following my own advice, and I am building a new cryptosystem. I have found this book a more valuable resource than any other book on cryptography that I have yet read. Even if you aren't building your own cryptosystem, I think you will find the insights this book has into complexity and design to be useful tools in evaluating other cryptosystems.

As one other reader pointed out this book can be called Applied Cryptography Light. It is true, it gives you more theory and very little math. I did not like this book by itself since I was interested in actual implementation and i wanted to see full algorithms and math. I did end up buying Applied Cryptography and those 2 books combined provide an excellent reference. I was not able to give more than 3 stars since I did not feel i got any knowledge out of this book to be able to apply it in real life except reading: "Cryptography is hard, you might need to hire an expert..." while I want to become an expert myself one day!