The Code Book by Simon Singh Read Free Book Online Page B

cipher, one that Soro might not have been able to break.
    Elsewhere in Europe, other courts were also beginning to employ skilled cryptanalysts, such as Philibert Babou, cryptanalyst to King Francis I of France. Babou gained a reputation for being incredibly persistent, working day and night and persevering for weeks on end in order to crack an intercepted message. Unfortunately for Babou, this gave the king ample opportunity to carry on a long-term affair with his wife. Toward the end of the sixteenth century the French consolidated their codebreaking prowess with the arrival of François Viète, who took particular pleasure in cracking Spanish ciphers. Spain’s cryptographers, who appear to have been naive compared with their rivals elsewhere in Europe, could not believe it when they discovered that their messages were transparent to the French. King Philip II of Spain went as far as petitioning the Vatican, claiming that the only explanation for Viète’s cryptanalysis was that he was an “archfiend in league with the devil.” Philip argued that Viète should be tried before a Cardinal’s Court for his demonic deeds; but the Pope, who was aware that his own cryptanalysts had been reading Spanish ciphers for years, rejected the Spanish petition. News of the petition soon reached cipher experts in various countries, and Spanish cryptographers became the laughingstock of Europe.
    The Spanish embarrassment was symptomatic of the state of the battle between cryptographers and cryptanalysts. This was a period of transition, with cryptographers still relying on the monoalphabetic substitution cipher, while cryptanalysts were beginning to use frequency analysis to break it. Those yet to discover the power of frequency analysis continued to trust monoalphabetic substitution, ignorant of the extent to which cryptanalysts such as Soro, Babou and Viète were able to read their messages.
    Meanwhile, countries that were alert to the weakness of the straightforward monoalphabetic substitution cipher were anxious to develop a better cipher, something that would protect their own nation’s messages from being unscrambled by enemy cryptanalysts. One of the simplest improvements to the security of the monoalphabetic substitution cipher was the introduction of nulls , symbols or letters that were not substitutes for actual letters, merely blanks that represented nothing. For example, one could substitute each plain letter with a number between 1 and 99, which would leave 73 numbers that represent nothing, and these could be randomly sprinkled throughout the ciphertext with varying frequencies. The nulls would pose no problem to the intended recipient, who would know that they were to be ignored. However, the nulls would baffle an enemy interceptor because they would confuse an attack by frequency analysis. An equally simple development was that cryptographers would sometimes deliberately misspell words before encrypting the message. Thys haz thi ifekkt off diztaughting thi ballans off frikwenseas—making it harder for the cryptanalyst to apply frequency analysis. However, the intended recipient, who knows the key, can unscramble the message and then deal with the bad, but not unintelligible, spelling.
    Another attempt to shore up the monoalphabetic substitution cipher involved the introduction of codewords. The term code has a very broad meaning in everyday language, and it is often used to describe any method for communicating in secret. However, as mentioned in the Introduction, it actually has a very specific meaning, and applies only to a certain form of substitution. So far we have concentrated on the idea of a substitution cipher, whereby each letter is replaced by a different letter, number or symbol. However, it is also possible to have substitution at a much higher level, whereby each word is represented by another word or symbol—this would be a code. For example,

    Technically, a code is defined as substitution at the level