Читать книгу Cryptography, Information Theory, and Error-Correction - Aiden A. Bruen - Страница 52

In examining these methods for breaking the Vigenère cipher, we have stated many times that these methods are only probabilistic, that is, they are only likely to work, not guaranteed. It is possible that we could go through the above process, only to decipher a given cipher text incorrectly. The question of how many messages encipher to a given cipher text is discussed in Chapter 15, and it turns out that we can roughly expect there to be only one intelligible message fitting with a given cipher text when the cipher text has more than 28 letters.