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The Trithemius cipher, however, provided a progressive, rather rigid and predictable system for switching between cipher alphabets. [note 1] In 1586 Blaise de Vigenère published a type of polyalphabetic cipher called an autokey cipher – because its key is based on the original plaintext – before the court of Henry III of France. [7]
The number of "coincidences" goes up sharply when the bottom message is shifted by a multiple of the key length, because then the adjacent letters are in the same language using the same alphabet. Having found the key length, cryptanalysis proceeds as described above using frequency analysis .
It is very similar to the Vigenère cipher, making many scholars call Bellaso its inventor, although unlike the modern Vigenère cipher Bellaso didn't use 26 different "shifts" (different Caesar's ciphers) for every letter, instead opting for 13 shifts for pairs of letters. The system is still periodic although the use of one or more long ...
On Vigenère's trips to Italy he read books about cryptography and came in contact with cryptologists. Giovan Battista Bellaso described a method of encryption in his 1553 book La cifra del. Sig. Giovan Battista Belaso, published in Venice in 1553, [16] which in the 19th century was misattributed to Vigenère and became widely known as the "Vigenère cipher". [17]
The Alberti cipher by Leon Battista Alberti around 1467 was an early polyalphabetic cipher. Alberti used a mixed alphabet to encrypt a message, but whenever he wanted to, he would switch to a different alphabet, indicating that he had done so by including an uppercase letter or a number in the cryptogram.
"The Alphabet Cipher" was a brief study published by Lewis Carroll in 1868, describing how to use the alphabet to send encrypted codes. [1] It was one of four ciphers he invented between 1858 and 1868, and one of two polyalphabetic ciphers he devised during that period and used to write letters to his friends. [2]
1854 – Charles Wheatstone invents the Playfair cipher; c. 1854 – Babbage's method for breaking polyalphabetic ciphers (pub 1863 by Kasiski) 1855 – For the English side in Crimean War, Charles Babbage broke Vigenère's autokey cipher (the 'unbreakable cipher' of the time) as well as the much weaker cipher that is called Vigenère cipher ...
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