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From: nather@ut-sally.UUCP (Ed Nather)
Newsgroups: comp.arch
Subject: Re: random number generator in hardware
Message-ID: <6364@ut-sally.UUCP>
Date: Sun, 16-Nov-86 14:42:49 EST
Article-I.D.: ut-sally.6364
Posted: Sun Nov 16 14:42:49 1986
Date-Received: Sun, 16-Nov-86 20:21:19 EST
References: <317@zuring.mcvax.UUCP> <267@bath63.UUCP>, <2490@phri.UUCP> <7320@utzoo.UUCP>
Organization: U. Texas CS Dept., Austin, Texas
Lines: 30

In article <7320@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes:
> > 	Which brings up a point which has been bothering me for a long
> > time.  Why don't computers come with hardware random number generators?
> > It doesn't seem like it would be too hard (i.e. expensive) to build a bank
> > of 32 white noise generators hooked up to zero-crossing detectors...
> 
> My understanding is that the problem is avoiding bias in the resulting
> numbers.  Building a noise generator isn't hard, but one would like the
> probability of a 0 to be roughly equal to the probability of a 1.  Getting
> this sort of balance, and *keeping* it, apparently is almost impossible
> without constant tweaking.  It's viable for specialized applications like
> generating encryption keys, but too much hassle to be built into every
> computer.
> 

There are several different ways to build a "hardware random number generator"
mostly based on the detection of radiactive decay, which is a completely
random process.  When I proposed such a scheme to Computer Scientist who
wanted a fast one, he replied "Oh, I don't want anything THAT random!"
What he was trying to explain was that he would be unable, with such a
device, to reproduce the same set of numbers again and again, which he would
need to debug the program calling for the random number.  And indeed, by
definition, you wouldn't get the same set of numbers twice -- if you did,
the generator would be broken!

-- 
Ed Nather
Astronomy Dept, U of Texas @ Austin
{allegra,ihnp4}!{noao,ut-sally}!utastro!nather
nather@astro.AS.UTEXAS.EDU