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Date:      Sat, 22 Jul 2000 16:36:14 +0200
From:      Poul-Henning Kamp <phk@critter.freebsd.dk>
To:        "Louis A. Mamakos" <louie@TransSys.COM>
Cc:        Brian Fundakowski Feldman <green@FreeBSD.ORG>, Kris Kennaway <kris@FreeBSD.ORG>, arch@FreeBSD.ORG
Subject:   Re: Quantifying entropy 
Message-ID:  <406.964276574@critter.freebsd.dk>
In-Reply-To: Your message of "Sat, 22 Jul 2000 10:32:24 EDT." <200007221432.KAA66024@whizzo.transsys.com> 

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In message <200007221432.KAA66024@whizzo.transsys.com>, "Louis A. Mamakos" writ
es:

>I think we're overestimating the extent of the threat.  Hell, an attacker
>could fire a particle beam at phk's geiger counter and comprise it as well.

Actually, he would just give me more random bits that way :-)

The way to use a geiger is to time three events:

	e1	e2	e3
	 |-T1---|---T2--|

	if T1 > T2
		bit == 0
	else if T1 < T2
		bit == 1
	else
		try_again;

And invert every other bit to remove any systematic bias.

--
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD coreteam member | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.


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