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Date:      Mon, 23 Oct 2006 19:37:12 +0200
From:      Roland Smith <rsmith@xs4all.nl>
To:        freebsd-stable@freebsd.org, matthieu.michaud@epita.info
Subject:   Re: VIA C7 support
Message-ID:  <20061023173712.GA17079@slackbox.xs4all.nl>
In-Reply-To: <20061023172712.GA16379@slackbox.xs4all.nl>
References:  <45393A29.3080100@epita.info> <200610231649.k9NGnLgQ065468@lurza.secnetix.de> <20061023172712.GA16379@slackbox.xs4all.nl>

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On Mon, Oct 23, 2006 at 07:27:12PM +0200, Roland Smith wrote:
> On Mon, Oct 23, 2006 at 06:49:21PM +0200, Oliver Fromme wrote:
> > Matthieu Michaud wrote:
> >  > Oliver Fromme wrote:
> >  > > Also take into account that you usually don't read that
> >  > > much data from /dev/random.  Quality is much more important
> >  > > than speed.
> >  >=20
> >  > you are right. do you know an easy way to evaluate this quality ?
> >=20
> > There is no easy way, I'm afraid.
>=20
> Start reading here: http://www.random.org/essay.html
> And follow the links.
>=20
> A test of 1 MB random data with "ent" [http://www.fourmilab.ch/random/]:
>=20
> dd if=3D/dev/random of=3Drand.dat bs=3D1k count=3D1k
> ./ent rand.dat=20
> Entropy =3D 7.999843 bits per byte.
>=20
> Optimum compression would reduce the size
> of this 1048576 byte file by 0 percent.
>=20
> Chi square distribution for 1048576 samples is 227.43, and randomly
> would exceed this value 75.00 percent of the times.
>=20
> Arithmetic mean value of data bytes is 127.6223 (127.5 =3D random).
> Monte Carlo value for Pi is 3.133839164 (error 0.25 percent).
> Serial correlation coefficient is -0.000504 (totally uncorrelated =3D 0.0=
).
>=20
>=20
> According to the same fourmilab page this is quite decent. There is
> about 1 bit of entropy in approx. ~6000 bytes!=20

That should be 1 bit of _non_ entropy. Oops.

> The chi square value is
> of the same order as one generated by timing radioactive decay events.

Repeating the cycle of dd/ent commands gives varying values for the chi
square test. It probably depends on the ratio of random bytes that you
need versus the number of really random bytes harvested by the system.
=20
Roland

--=20
R.F.Smith                                   http://www.xs4all.nl/~rsmith/
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