By Damon Smith

DECEMBER 7, 1999: 

The Code Book: The Evolution of Secrecy from Mary, Queen of Scots to Quantum Cryptography by Simon Singh (Doubleday), 402 pages, $24.95.

Today corporations and civil libertarians routinely join forces in the US to lobby for secure encryption software, much to the dismay of law enforcers and the National Security Agency. Few parties would claim to understand the technology and mathematical logic behind such programs, however. In The Code Book, an admirably lucid account of the evolution of cryptography, Simon Singh writes of the codes and ciphers that have been used to ensure privacy from the ancient world to the computer age. As he did in his acclaimed book Fermat's Enigma, Singh masterfully weds historiography and science writing, carefully elucidating the often mind-boggling mechanics of encryption while spinning tales of political intrigue and skullduggery, wartime bravery and great mathematical ingenuity.

The Code Book is a highly entertaining guide to the world of enigmas and the peaks of human cleverness, an overview of world history seen through the x-ray goggles of a fun-loving scientist. "History is punctuated with codes," Singh writes in his introduction. "They have decided the outcomes of battles and led to the deaths of kings and queens." To reinforce this point, Singh recounts one of the most famous episodes in British history: the 16th-century plot to assassinate Queen Elizabeth. With the dramatic sense of an accomplished novelist, Singh tells how the plan was foiled when a government minister deciphered a letter sent by Mary Queen of Scots to her fellow Catholic conspirators -- a revelation that resulted in her execution, marking a turning point in the fate of Britain.

Singh uses this story primarily to illustrate the basic weakness of an encryption technique known as monoalphabetic substitution, which prevailed through the European Renaissance even though Arab scholars had learned long before to break it using frequency analysis. He explains that it was eventually replaced by the polyalphabetic Vigenère square, which protected military and government dispatches for 250 years, until the eccentric genius Charles Babbage (who developed a prototype for the first modern computer) discovered a method for cracking it in the mid 19th century.

Throughout his book, Singh tantalizes the reader with fascinating stories of how ciphers have played a role not only in historical events but in some of Western civilization's best-kept secrets, such as the mysterious identity of the Man in the Iron Mask, made famous by Alexandre Dumas. He also relates the story of the Beale treasure, a $20 million fortune amassed in the Old West and buried somewhere in Virginia, the directions to which are contained in a set of encrypted papers that have thus far eluded the sharpest analytic minds, not to mention professional treasure hunters. Part of the allure of these tales is that Singh has a special talent for creating suspense, revealing just enough information to engage one's imagination, but cloaking the essential details until the last possible moment.

In addition to charting the development of encryption practices, one of Singh's primary objectives is to show how the indefatigable efforts of cryptanalysts -- those who decipher coded messages -- have spurred important scientific advancements. For instance, the invention of radio at the turn of the century made it easier for government cryptanalysts to gather intelligence, as anyone with an antenna could easily intercept enemy communications, but it also drove the need for stronger encryption methods. This eventually resulted in the "mechanisation of secrecy," the creation of machines to scramble messages beyond the pen-wielding abilities of human beings, which has given rise to the public-key cryptography widely used today by businesses and governments.

Another theme of The Code Book is the ongoing struggle between code makers and code breakers, a dynamic Singh characterizes as "an intellectual arms race that has had a dramatic impact on the course of history." Certainly this was the case during the First and Second World Wars. Singh tells the story of Alan Turing, a brilliant mathematician who devoted himself to the war effort at Bletchley Park and helped to crack the Enigma code machines used by the Nazis. Turing and his colleagues' breakthroughs prevented U-boat attacks and ultimately shortened World War II, but because of the British intelligence community's policy of maintaining secrecy for its operations, his important work was never recognized.

Delicately approaching the subject of binary code (the language of computers) in the final chapters, Singh manages to give a cogent explanation of how software encryption developed from modular arithmetic, one-way functions, and huge prime numbers without losing the careful balance between suspenseful narrative and technical detail. And he presents the latest theories on how a truly unbreakable code -- a far-out system based on the emission of polarized photons -- may be at the doorstep of scientific knowledge.

The only criticism one might make of The Code Book is that Singh occasionally coddles the reader, overexplaining fundamental ideas or rehashing problems he's already elaborated fully. Still, that kind of repetition is reassuring to the nontechnical reader. Peppering the text with graphs and diagrams, the former BBC producer just wants to make sure anyone can follow along on his journey. People with a general interest in world history, linguistics, or mathematics, and especially crossword fanatics, will find this fascinating survey of secret writing particularly hard to put down.

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