Re: [RFC][PATCH] Make cryptoapi non-optional?

Andries Brouwer
2003-08-15T07:55:09Z

On Fri, Aug 15, 2003 at 12:40:04AM -0700, David S. Miller wrote:
> Andries Brouwer <aebr@win.tue.nl> wrote:
>
> > On Thu, Aug 14, 2003 at 06:17:13PM -0600, Val Henson wrote:
> >
> > > entropy(x) >= entropy(x xor y)
> > > entropy(y) >= entropy(x xor y)
> >
> > Is this trolling? Are you serious?
>
> These lemma are absolutely true.

David, did you read this line:

> > Try to put z = x xor y and apply your insight to the strings x and z.

Let us do it. Let z be an abbreviation for x xor y.

The lemma that you believe in, applied to x and z, says

entropy(x) >= entropy(x xor z)
entropy(z) >= entropy(x xor z)

But x xor z equals y, so you believe for arbitrary strings x and y that

entropy(x) >= entropy(y)
entropy(x xor y) >= entropy(y).

This "lemma", formulated in this generality, is just plain nonsense.

Andries