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1.1.2 The Arab Cryptanalysts
• The year 750 heralded the golden age of Islamic civilization. The arts and sciences flourished in equal measure. The legacy of Islamic scientists is evident from the number of Arabic words that pepper the lexicon of modern science, such as algebra, alkaline, zenith. The social order relied on an effective system of administration, which in turn relied on secure communication achieved through the use of encryption.
• This monoalphabetic substitution cipher used symbols as well as letters.
• The Arab scholars invented cryptanalysis, the science of unscrambling a message without knowledge of the key. They cracked the monoalphabetic substitution cipher after several centuries of its successful use. This would not have been possible in a society until it had reached a sufficiently sophisticated level of scholarship in mathematics, statistics, and linguistics.
• The innocuous observation that some letters are more common than others in written documents would lead to the first great breakthrough in cryptanalysis. The method, called
frequency analysis is described in a treatise by Abu Yusuf Ya’qub ibn Is-haq ibn as-Sabbah ibn ‘omran ibn Ismail al-Kindi (let’s call him al-Kindi for short) in the ninth century.
• Table 1 on page 19 give the relative frequency of each letter of the English alphabet and is based on newspaper articles and novels. "e" is the most common letter, followed by "t" and then "a", and so on.
• In general, short texts are likely to deviate significantly from the standard frequencies, and if there are less than a hundred letters, then decipherment will be very difficult.
A counterexample:
La Disparition, and its translation into English (Appendix A, a 200-page novel that did not use any words containing the letter "e"!
• Besides logical thinking, frequency analysis requires guile, intuition, flexibility, and guesswork.
...
https://www.math.uci.edu/~brusso/freshman6.pdf
• The year 750 heralded the golden age of Islamic civilization. The arts and sciences flourished in equal measure. The legacy of Islamic scientists is evident from the number of Arabic words that pepper the lexicon of modern science, such as algebra, alkaline, zenith. The social order relied on an effective system of administration, which in turn relied on secure communication achieved through the use of encryption.
• This monoalphabetic substitution cipher used symbols as well as letters.
• The Arab scholars invented cryptanalysis, the science of unscrambling a message without knowledge of the key. They cracked the monoalphabetic substitution cipher after several centuries of its successful use. This would not have been possible in a society until it had reached a sufficiently sophisticated level of scholarship in mathematics, statistics, and linguistics.
• The innocuous observation that some letters are more common than others in written documents would lead to the first great breakthrough in cryptanalysis. The method, called
frequency analysis is described in a treatise by Abu Yusuf Ya’qub ibn Is-haq ibn as-Sabbah ibn ‘omran ibn Ismail al-Kindi (let’s call him al-Kindi for short) in the ninth century.
• Table 1 on page 19 give the relative frequency of each letter of the English alphabet and is based on newspaper articles and novels. "e" is the most common letter, followed by "t" and then "a", and so on.
• In general, short texts are likely to deviate significantly from the standard frequencies, and if there are less than a hundred letters, then decipherment will be very difficult.
A counterexample:
La Disparition, and its translation into English (Appendix A, a 200-page novel that did not use any words containing the letter "e"!
• Besides logical thinking, frequency analysis requires guile, intuition, flexibility, and guesswork.
...
https://www.math.uci.edu/~brusso/freshman6.pdf
