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

[Nick Piggin]

Måns Rullgård wrote:

> Andries Brouwer <aebr@xxxxxxxxxx> writes:
>
>
> > > > > 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.
>
> Not quite non-sense, but it would mean that for any strings x and y, 
>
>  entropy(x) == entropy(y),
>
> which seems incorrect.

Well, just the line entropy(x) >= entropy(y) is incorrect. ie. proof
by contradiction.


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