[MKS] Re: A Question of Permutations of Vectors of Bits

From: Simon G Best (s.g.best_at_btopenworld.com)
Date: 07/31/03 

Date: Thu, 31 Jul 2003 09:49:11 +0000 (UTC)

Mok-Kong Shen wrote:
>
> The problem arose with your saying a permutation of bits,
> which one would commonly understand to be a shuffling
> of bits.

I never said "a permutation of bits," I said, "a permutation of 2n-bit
vectors."

> A block cipher maps 2^n blocks, each containing
> n bits, to 2^n such blocks. That mapping is a permutation
> of the elements (each a block) of a sequence of length
> 2^n to another such sequence (because a block cipher
> does a bijecive mapping). So you should say P is
> a block encryption function or P is a bijective mapping
> of the space of n-bit entities to itself, in order
> to avoid confusion. (You see I am not the single person
> who got confused).
>
> M. K. Shen

I'd already cleared up the confusion. You even read the post in which I
cleared up the confusion (my first reply to David Wagner). Yet you
*are* "the single person" who (apparently) remained confused for five
more posts. And now you're telling me what I "should say" in order to
avoid confusion!

Here's the bit from my first reply to David Wagner:-

> I meant a bijective mapping of 2n-bit vectors to 2n-bit vectors;
> a permutation such as a block cipher's encryption function with
> a particular key.

I know you read that, because you yourself - in your first post in this
thread - said, "Your second post said that P is like a block cipher with
a particular key."

Despite that, you have subsequently ignored what I'd said, and are now
telling me that I should say, "P is a block encryption function or P is
a bijective mapping of the space of n-bit entities to itself," as if I
hadn't already said it several posts ago!

Simon