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Vigenère cipher

The Vigenère cipher, like the Caesar cipher, is a substitution cipher, but unlike the Caesar cipher, it uses multiple ciphertext alphabets that are applied repeatedly. Unlike the Caesar cipher, which uses monoalphabetic substitution, the Vigenère cipher involves polyalphabetic substitution.

The Vigenère method is an encryption method that is several hundred years old and uses multiple key alphabets. When ciphering a plaintext letter, one key alphabet is used, and when ciphering the following plaintext letter, another key alphabet is used. The plaintext letters are individually ciphered with the alphabetically shifted letters of the keyword.

Vigenère cipher, where the plaintext has been encrypted with the ciphertext word 'cipher'.

Vigenère cipher, where the plaintext has been encrypted with the ciphertext word 'cipher'.

In the example, the first letter from the plaintext is in "S", which is encrypted with the offset letter of the keyword. The letter "C" from the keyword has an alphabetic offset of three, as it is third in the alphabet. If you now offset the letter "S" by three places, then the "S" encrypted becomes the "V". "H", the second letter of the keyword has an offset of eight, this leads to the second plaintext letter, the "U", to the ciphered letter "C", and so on. In principle, the Vigenère cipher uses the Caesar method several times.

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Englisch: Vigenère cipher
Updated at: 07.03.2019
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