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Vigenère cipher

Like the Caesar cipher, the Vigenère cipher is a substitution cipher, but unlike the Caesar cipher, it works with 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. One key alphabet is used when ciphering a plaintext letter, and another is used when ciphering the following plaintext letter. The plaintext letters are individually ciphered with the alphabetically shifted letters of the keyword.

Vigenère cipher, where the plaintext was encrypted with the ciphertext word

Vigenère cipher, where the plaintext was 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, since it is in the third position of 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.

Englisch: Vigenère cipher
Updated at: 07.03.2019
#Words: 210
Links: Caesar cipher, substitution cipher, ciphertext (CT), method, encryption method
Translations: DE

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