Re: [NEWBIE]vigenere

Mike Amling wrote:

> If the set of plaintexts and the set of ciphertexts have order N, then
> the set of keys of a perfect cipher must have order which is >=N and
> <=N!, and for each ciphertext c, the total probability of the keys that
> map plaintext p to c must equal the total probability of the keys that
> map plaintext q to c, for all p and q.
> There are quite a few perfect ciphers, and I don't see how you can
> claim that each of them is "adding" a key "to the plaintext".

The properties of a perfect cipher, as you stated above, are directly
equivalent to the properties of addition within a group.

> What is the group operation?

That depends on the isomorphism.
Received on Tue Jan 17 16:50:31 2006