Quello che ho postato prima, l'ho preso dal libro "computer network capitolo 8.1.4".
Posto anche l'esempio che segue subito dopo il paragrafo del post precedente...è molto semplice e ti fa capire perchè questo cifrario è sicuro

An example of how one-time pads are used is given in Fig. 8-4. First, message 1, ''I love you.'' is converted to 7-bit ASCII. Then a one-time pad, pad 1, is chosen and XORed with the message to get the ciphertext. A cryptanalyst could try all possible one-time pads to see what plaintext came out for each one. For example, the one-time pad listed as pad 2 in the figure could be tried, resulting in plaintext 2, ''Elvis lives'', which may or may not be plausible (a subject beyond the scope of this book). In fact, for every 11-character ASCII plaintext, there is a one-time pad that generates it. That is what we mean by saying there is no information in the ciphertext: you can get any message of the correct length out of it.