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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

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.


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