Thursday, February 9, 2023

Cryptography

Babbage achieved notable results in cryptography, though this was still not known a century after his death. Letter frequency was category 18 of Babbage's tabulation project. Joseph Henry later defended interest in it, in the absence of the facts, as relevant to the management of movable type.[125]

As early as 1845, Babbage had solved a cipher that had been posed as a challenge by his nephew Henry Hollier, and in the process, he made a discovery about ciphers that were based on Vigenère tables. Specifically, he realised that enciphering plain text with a keyword rendered the cipher text subject to modular arithmetic.[136] During the Crimean War of the 1850s, Babbage broke Vigenère's autokey cipher as well as the much weaker cipher that is called Vigenère cipher today.[137] His discovery was kept a military secret, and was not published. Credit for the result was instead given to Friedrich Kasiski, a Prussian infantry officer, who made the same discovery some years later.[138] However, in 1854, Babbage published the solution of a Vigenère cipher, which had been published previously in the Journal of the Society of Arts.[136][139] In 1855, Babbage also published a short letter, "Cypher Writing", in the same journal.[140] Nevertheless, his priority was not established until 1985.[136][141]

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