another feature RNGs could provide

[Travis H.]

On 12/21/05, Perry E. Metzger <perry at piermont.com> wrote:
> > Good ciphers aren't permutations, though, are they? Because if they
> > were, they'd be groups, and that would be bad.
>
> Actually, by definition, a cipher should be a permutation from the set
> of plaintexts to the set of ciphertexts. It has to be 1 to 1 bijective
> or it isn't an encryption algorithm.

Isn't the question people normally care about whether encryption over
all keys is closed or not, and only relevant if you're trying to
increase the keyspace through multiple encryption?

The other day I was thinking of using a very large key to select a
permutation at random from the symmetric group S_(2^x).  That would be
a group, but I don't see how you knowing that I'm using a random
permutation would help you at all.
--
http://www.lightconsulting.com/~travis/
"I once went to a mathematics conference.  I got the room number Pi.  It was
easy to find, but took forever to dial on the in-house phone." -- Steven Wright
GPG fingerprint: 50A1 15C5 A9DE 23B9 ED98 C93E 38E9 204A 94C2 641B

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