Encrypt

It was probably religiously motivated textual analysis of the Qur’an which led to the invention of the frequency analysis technique for breaking monoalphabetic substitution ciphers sometime around 1000 CE (Ibrahim Al-Kadi -1992). It was the most fundamental cryptanalytic advance until WWII. Essentially all ciphers remained vulnerable to this cryptanalytic technique until the invention of the polyalphabetic cipher by Alberti (ca 1465), and many remained so thereafter.[citation needed]

Although Alberti is usually considered the father of polyalphabetic cipher, Prof. Al-Kadi’s 1990 paper (ref- 3), reviewing Arabic contributions to cryptography reported knowledge of polyalphabetic ciphers 500 years before Alberti, based on a recently discovered manuscript).

It appears that Abu Yusuf Yaqub ibn Is-haq ibn as Sabbah ibn ‘omran ibn Ismail Al- Kindi, who wrote a book on crytography called “Risalah fi Istikhraj al-Mu’amma” (Manuscript for the Deciphering Cryptographic Messages), circa 750 CE), may have described cryptanalysis techniques (including some for polyalphabetic ciphers), cipher classification, Arabic Phonetics and Syntax, and, most importantly, described the use of several statistical techniques for cryptanalysis. [This book seems to be the first post-classical era reference by about 300 years.] It also contains probability and statistical work some 800 years before Pascal and Fermat.

Cryptography became (secretly) still more important as a consequence of political competition and religious revolution. For instance, in Europe during and after the Renaissance, citizens of the various Italian states — the Papal States and the Roman Catholic Church included — were responsible for rapid proliferation of cryptographic techniques, few of which reflect understanding (or even knowledge) of Alberti’s polyalphabetic advance. ‘Advanced ciphers’, even after Alberti, weren’t as advanced as their inventors / developers / users claimed (and probably even themselves believed). They were regularly broken. This over-optimism may be inherent in cryptography for it was then, and remains today, fundamentally difficult to really know how vulnerable your system actually is. In the absence of knowledge, guesses and hopes, as may be expected, are common.

Cryptography, cryptanalysis, and secret agent/courier betrayal featured in the Babington plot during the reign of Queen Elizabeth I which led to the execution of Mary, Queen of Scots. An encrypted message from the time of the Man in the Iron Mask (decrypted just prior to 1900 by Étienne Bazeries) has shed some, regrettably non-definitive, light on the identity of that real, if legendary and unfortunate, prisoner. Cryptography, and its misuse, were involved in the plotting which led to the execution of Mata Hari and in the conniving which led to the travesty of Dreyfus’ conviction and imprisonment, both in the early 20th century. Fortunately, cryptographers were also involved in exposing the machinations which had led to Dreyfus’ problems; Mata Hari, in contrast, was shot.

Outside of Europe, after the end of the Muslim Golden Age at the hand of the Mongols, cryptography remained comparatively undeveloped. Cryptography in Japan seems not to have been used until about 1510, and advanced techniques were not known until after the opening of the country to the West beginning in the 1860s.

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