lkml.org 
[lkml]   [2003]   [Aug]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC][PATCH] Make cryptoapi non-optional?
On Sat, Aug 16, 2003 at 06:27:44AM +0000, David Wagner wrote:
> Val Henson wrote:
> >If entropy(x) == entropy(y), then:
> >
> >entropy(x) >= entropy(x xor y)
> >entropy(y) >= entropy(x xor y)
>
> No, that's still wrong. Please see my earlier email with a counterexample.
> That counterexample disproves not only the earlier claim, but also this more
> recent revised claim.

Sigh. Yes, I was thinking of the case where x and y already have
maximum entropy, in which case

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

For any y. The point I was really trying to make (badly) is that
xoring won't increase entropy on average in this particular case
(folding the output of SHA-1). In other words, xoring won't make
anything better, and has the possibility of making things worse. In
any way I evaluate it, folding and truncating are just as good for
this particular case, except that folding costs more
computationally. (The computational cost was significant enough to
have a measurable effect on throughput, so I'm not arm-chair
optimizing here.)

I sacrifice any earlier points I attempted to make on the altar of
hasty mathematics.

-VAL
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:47    [W:0.141 / U:0.224 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site