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

Måns Rullgård
2003-08-15T08:06:48Z

Andries Brouwer <aebr@win.tue.nl> 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.

--
Måns Rullgård
mru@users.sf.net