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Timeline of notable cryptology events (in white), spanning 500 CE up to 1500 CE. Includes notable linguistic, scientific and anthropological events of contextual importance (in blue). Click on More » for more information.

725 CE to 790 CE

Abu Abd al-Rahman al-Khalil ibn Ahmad ibn Amr ibn Tammam al Farahidi al-Zadi al Yahmadi writes the first book devoted to the subject of plaintext-attack cryptanalysis. Yahmadi solved a Byzantine cryptographic puzzle written in Greek by guessing that the puzzle began with "In the name of God". Based on that assumption, he figured out the rest of the text.
850 CE

Arab polymath Abu-Yusuf Ya’qub ibn Ishaq al-Kindi writes A Manuscript on Deciphering Cryptographic Messages, the first known recorded explanation of frequency analysis.
855 CE

Abu Bakr Ahmad ben `Ali ben Wahshiyya an-Nabati publishes Kitab Shawq al-Mustaham which details several cipher alphabets for mystical use.
963 CE to 1187 CE

The Ghaznavid empire (which covers much of present day Iran, Afghanistan, northwest India and Pakistan) utilizes ciphertext in government documents. High officials were supplied with a personal cipher before setting out for new posts.
1226 CE

Political cryptography spreads through Venice, Rome, the Vatican, the secular principalities of Italy, and throughout Europe
1250 CE

English philosopher and alchemist Roger Bacon writes Epistola de Secretis Operibus Artis et Naturae, et de Nullitate Magiae (The Secret Works of Art and of Nature and Also on the Nullity of Magic) in which seven cipher methods are listed. The last three chapters are written in a cryptogramic alchemical jargon. Note the last five words in this passage:
We can, with saltpeter and other substances, compose artificially a fire that can be launched over long distances... By only using a very small quantity of this material much light can be created accompanied by a horrible fracas. It is possible with it to destroy a town or an army ... In order to produce this artificial lightning and thunder it is necessary to take saltpeter, sulfur, and Luru Vopo Vir Can Utriet.
The last five gibberish words are an anagram that conceals the proportion of powdered charcoal needed to make the explosive.

Bacon also notes:"a man is crazy who writes a secret in any other way than one which will conceal it from the vulgar."
1377 CE

Arab historian Ibn Khaldun writes the Muqaddimah, the first of a seven part universal history. Topics include ciphers used by tax and army bureaus:
They use a very special code among themselves, which is like a puzzle. It makes use of the names of perfumes, fruits, birds, or flowers to indicate the letters, or it makes use of forms different from the accepted forms of the letters. Such a code is agreed upon by the correspondents between themselves, in order to be able to convey their thoughts in writing.
1379 CE

The first European cryptography manual appears. It is a collection of ciphers by Gabrieli di Lavinde. The manual describes nomenclator cryptosystems, which combine a codebook with homophonic substitution. Until the 19th century, nomenclators enjoyed widespread use in the trading states of southern Europe and the Catholic Church. They were superceded by commercial codes which provided greater economy of transmission.
1392 CE

The Equatorie of the Planetis is written. This treatise on astronomy is sometimes attributed to Geoffrey Chaucer. It includes six passages written in a substitution cipher of letters, numbers and symbols.
1412 CE

Shihab al-Din abu `l-`Abbas Ahmad ben `Ali ben Ahmad `Abd Allah al-Qalqashandi writes the Subh al-a 'sha, a 14-volume encyclopedia that includes a two-part chapter on cryptography, including substitution and transposition ciphers. Also mentioned is the technique for encrypting a plaintext via multiple substitution ciphers.
1466 CE

Italian polymath Leon Battista Alberti publishes Trattati in cifra (A Treatise on Ciphers). Alberti invented the polyalphabetic cipher and machine-assisted encryption using his cipher disk (Captain Midnight Decoder Badge) to simplify the process.
1473 CE

A manuscript by Arnaldus de Bruxella uses five lines of cipher to conceal the crucial part of the operation of making a philosopher's stone.
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