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Re: [Demexp-dev] VIA x86-like processors with cryptographic facilities

From: Brian Hurt
Subject: Re: [Demexp-dev] VIA x86-like processors with cryptographic facilities
Date: Sun, 19 Sep 2004 17:27:44 -0500 (CDT)

On Sun, 19 Sep 2004, David MENTRE wrote:

> And BTW, it is possible that the random generator is not a proper
> generator based on a physical device like thermal noise. But, in that
> case, cryptographically hashing them wouldn't help: if the source of the
> cryptographic hash is predictable, then the hashed value is
> predictable. That's why having a real source of randomness is important.

IIRC, they added a delibertly noisy circuit they sample.  And then they
try to clean up the sample.  Note that all I said is that I'd be concerned
with bias.  In the simple case, this means that a bit is more likely to be
(for example) a 1 instead of a 0.  This bias may be very small- say,
50.0000001% 1's vr.s 49.9999999% 0's.  Or maybe more severe- say 60% 1's
and 40% 0's.  This would make it easier to figure out what the random
source was- certain input numbers become signifigantly more probable than
others.  You try the probable ones first.

But there is still random information there.  Even if the number is 70%
1's and 30% 0's, you're still getting (approximately) 0.6 bits of random
information per bit (actually, it's a little bit less than this- I'm
forgetting the actual formula at the moment).  So if you need 256 bits of
truely random bits, you'd need to collect 256/0.6 or 427 bits of biased
bits, and then hash the value down to 256 bits, "concentrating" the

Personally, I don't think cryptography is going to be the problem area.  
Well, maybe on the server- although I'd bet DB is going to be more
expensive.  On the client side, I think a 1MHz 8-bit CPU would have enough
HP for what we want.  On the client side, the constraints is going be
cost, especially cost of the video.

Although, if we could find a really cheap PCI video card (we're not using
the machines for games), I'd be tempted to go with a cheap PPC or 68K or
ARM.  All of which I know have PCI bus master capabilities built in.

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