Vigenère cipher

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The Vigenère cipher (French pronunciation: [viʒnɛːʁ]) is a method of encrypting alphabetic text where each letter of the plaintext is encoded with a different Caesar cipher, whose increment is determined by the corresponding letter of another text, the key. In a Caesar cipher, each letter of the alphabet is shifted along some number of places. In a Caesar cipher of shift 3, a would become D, b would become E, y would become B and so on. The Vigenère cipher has several Caesar ciphers in sequence with different shift values. For example, if the plaintext is attacking tonight and the key is oculorhinolaryngology, then the first letter of the plaintext, a, is shifted by 14 positions in the alphabet (because the first letter of the key, o, is the 14th letter of the alphabet, counting from zero), yielding o; the second letter, t, is shifted by 2 (because the second letter of the key, c, is the 2nd letter of the alphabet, counting from zero) yielding v; the third letter, t, is shifted by 20...

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