Another chromatic review, this time of Disappearing Cryptography. It is a fortunate circumstance that even as governments -- and others -- are becoming more interested in peering over your shoulder, or at least at your data traffic, the exchange of large files suitable for hiding messages has become commonplace. Peter Wayner is also the author of Free For All , reviewed here on Slashdot a few months back.
The ScoopCryptography, argues the author, has the potential to balance power relationships between individuals and governments. Forcing people to conduct all communications in publicly-readable forms allows the honest to be oppressed by tyrants, criminals, and pranksters. Why should the innocent suffer to help authories track stupid criminals?
Wayner mainly concentrates on steganography, hiding secret communications in plain sight. Instead of using ciphers and algorithms to generate a message mathematically indistinguishable from pure random noise, one might instead replace the lowest significant bits of a JPG image with the message. Only those who analyze the image may potentially reconstruct the text.
What's to Like?Each chapter has three sections, arranged by increasing complexity. The first contains a short anecdote to illustrate the point of the chapter. (Some make immediate sense, while others seem only tangentially related.) The second section discusses the theory. The final section gets into the guts, mathematics and algorithms, analysis and common problems. This division allows readers to go only as deeply as they prefer.
Early sections on information theory lay the framework for later chapters. While discussions of error correction and density don't have the cloak and dagger thrill of spy stuff, they're fundamental to serious analysis of techniques. Serious students would do well to use Wayner's extensive and excellent bibliography of books and papers to improve their knowledge.
The middle of the book is excellent. A lengthy discussion of text mimicry starts with analysis techniques, producing in a program hiding a secret message in an innocent-seeming baseball play-by-play. (It includes a dissertation on effective and reversible context-free grammars.) The next chapter, on Turing machines and reversable computing, is particularly interesting (especially after reading The Diamond Age).
More than just data hiding, the final section of the text covers privacy. Anonymous remailers can provide double-blind communication (but see the caveat below). The Dining Cryptographers algorithm of chapter 11 may be used to send a secret message without divulging the sender's identity. The final chapter adds a philosophical spin, explaining the author's biases and his reasoning for promoting secrecy. (He's Cypherpunk friendly.)
What's to Consider?This is not a book for beginners. Some of the initial theory throws around summations and other pre-calculus constructs as an integral (pardon the pun) explanation of entropy. One of the two large examples is written in Pascal. A second year computer science student should have no trouble understanding the text. A layman might not get past the second chapter (though he could safely skip most of the math.)
This book is also dated -- in fact, Hemos recommended it for review partly to prompt the author and publisher to produce a new version. The anonymous remailer chapter is seriously out of date, and it would be nice to have new information about distributed.net, secure peer-to-peer communications, and web stuff. In addition, some of the softwares described have been superceded by new versions and successors.
The SummaryAging but written with the future in the mind, Disappearing Cryptography favors theory and principles, for the most part. It makes a good introduction to steganography and the study of patterns in digital communications, leading naturally to more detailed works. It may also serve as a starting point to new ideas and discussions. Perhaps 2001 will bring us a new version.
Table of Contents
- Framing Information
- Error Correction
- Secret Sharing
- Basic Mimicry
- Grammars and Mimicry
- Turing and Reverse
- Life in the Noise
- Anonymous Remailers
- Secret Broadcasts
- Mimic Code
- Baseball CFG
- Reversable Grammar Generator
You can purchase this book at Fatbrain.