Book review: Modern Cryptanalysis

Modern Cryptanalysis: Techniques for Advanced Code Breaking

The lack of the market for books on cryptography might be viewed as surprising. Given that the market can sustain over 200 books about PHP, how has a topic as sexy as cryptography not got more than a dozen or so books? It’s like the world saw Schneier’s Applied Cryptography and figured there wasn’t any point trying.

This isn’t actually that unreasonable. Schneier’s book might be showing its age these days, but trying to keep up with the leading edge of research is a game for mugs and crypto researchers, and neither one is in need of a textbook. The rest of us just need a primer on the principles of cryptography that covers the major protocols and widely-used algorithms without dumbing down, and if that’s what you’re after then Applied Cryptography is still the first and last book that need be on your list.

It does have one major hole, and that’s in the coverage of cryptanalysis. Admittedly, cryptanalysis is even further from the everyday reality of most developers than cryptograpy is: attempting to implement crypto algorithms yourself is risky and requires care, but attempting your own cryptanalysis of any non-trivial algorithm is a pointless exercise best reserved for a really rainy day, or just left to the experts. But I can’t have been the only one who feels very dissatisfied at knowing that something can be done, but not knowing how.

On the face of it, Modern Cryptanalysis is pretty much exactly the book I’ve been looking for all these years. It starts from modest assumptions about background knowledge, but covers real military-grade algorithms. It has good step-by-step tutorials and illustrates it with usable source code in Python. It’s reasonably priced (though certainly not cheap), and picks a good range of topics to get a reasonable overview of the field while still being a manageable length overall.

However, it left me feeling frustrated. A little too much time is spent on toy algorithms that are only of historical interest and are well covered by other books. It then attempts to teach the most basic mathematical background before ploughing into weighty topics in number theory such as factorisation and elliptic curves. In general I feel that the information on public-key systems was too much and too soon in the book: you can’t analyse RSA without postgraduate-level number theory. By the same token, not enough time was spent on symmetric block ciphers for my liking, as to me they strike a nice balance of being a rich topic that doesn’t require too much mathematical background for the casual reader to benefit from it.

Perhaps it was my relatively hurried reading of it, but I didn’t feel the explanations were quite clear enough, particularly in explaining linear and differential cryptanalysis. This was exacerbated by an extremely large number of typos, some of which occurred in mathematical expressions and obscured the meaning of the text.

Despite my reservations, this book actually does the job you most likely require of a book on cryptanalysis, which is to demystify it and give enough of a flavour that you know whether you want to read further. It’s not a classic, but it’s a fair starting point.

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