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Re: Entropy Patch with Linebreaks


From: Marcus Brinkmann
Subject: Re: Entropy Patch with Linebreaks
Date: Thu, 23 Aug 2007 13:07:30 +0200
User-agent: Wanderlust/2.14.0 (Africa) SEMI/1.14.6 (Maruoka) FLIM/1.14.8 (Shij┼Ź) APEL/10.6 Emacs/23.0.0 (i486-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO)

At Sun, 12 Aug 2007 11:47:28 +0200,
Samuel Thibault <samuel.thibault@ens-lyon.org> wrote:
> > +    /* Sune Kirkeby's entropy patch (which was a port of the
> > +       linux entropy drivers for GNU mach) placed the keyboard
> > +       entropy source here. I looked at that for an idea of where
> > +       how to do write this driver.  */
> > +   entropy_putchar(scancode | (up ? 0200 : 0), ENTROPY_LOW_QUALITY);
> 
> Why low quality? I know people always use the same commands (ls, mv...)
> but the order in which they type them is to my mind a very good source
> of entropy. Also, the _time_ when characters are typed should be the
> best source of entropy, you should really take that into account.

A careful analysis of "quality" produced by various sources can be found in:

Thomas Biege
Analysis of a strong Random Number Generator
http://www.suse.de/~thomas/papers/random-analysis.pdf

This paper does not include keyboard and mouse activity but focuses on
initialization at boot time.  Thus, more important than the result
(which, in summary, is that booting to a static configuration does not
produce good entropy) is the description of the methods used to
measure entropy.

It's a good idea to be conservative about entropy measurements.
Commonly it is overestimated by a large margin.

Thanks,
Marcus





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