Vigenere Cipher Algorithm

The Vigenere cipher is a polyalphabetic encryption algorithm that enciphers a message using a whole sequence of different Caesar cipher shifts rather than just one, with each letter of a repeating keyword setting the shift applied to the corresponding letter of the message. Despite carrying his name, the cipher was not invented by Blaise de Vigenere, who in 1586 actually described a different and stronger autokey cipher; the polyalphabetic method now known by his name was really devised by Giovan Battista Bellaso in 1553, and the two techniques were mixed up in later centuries. For roughly three hundred years the cipher was called le chiffre indechiffrable, the indecipherable cipher, and it genuinely resisted every attempt to break it until 1863, when Friedrich Kasiski published a general method of attack that exploited the repeating pattern created by a short keyword reused across a long message, finally ending its reputation for unbreakable security.