From: roy@sendai.cybrspc.mn.org (Roy M. Silvernail)
Date: Sun, 19 Jun 94 08:41:39 PDT
To: pfarrell@netcom.com (Pat Farrell)
Subject: Re: Hardware Random Numbers
In-Reply-To: <199406182254.PAA22537@netcom3.netcom.com>
Message-ID: <940619.094713.8w5.rusnews.w165w@sendai.cybrspc.mn.org>
MIME-Version: 1.0
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In list.cypherpunks, thus spake pfarrell@netcom.com (Pat Farrell):

> A while ago some folks talked about being willing to pay for
> a hardware random number generator. Not a PRNG, but a real
> one. There are lots of uses listed in TCMay's document that
> can't be named, but generating blinding factors for digital cash 
> is my favorite.
> 
> I've got a friend who is a professional electronics engineer that
> is willing to help, but he has some questions on the design.

[...]

> 3. Maybe it should go on the PC bus as an adapter card.

This is the way to go.  Serial port real estate is way too scarce in the
average PC.  Besides, this approach makes the design easier and has
another advantage...

> While I'd like to think that I really control my PC, once you get 
> networking TSRs, smartdrv, APSI drivers, CDROM and Soundcard drivers, 
> HIMEM, etc. loaded, do you really _know_ that they are your friends? 
> Is this a real problem?

Yes, this can be a real problem.  So design the card such that the noise
source runs continuously at a high speed, and feeds an 8-bit shift
register.  Place a latch on the output of the register, and set up
decoding logic to read the latch in a memory-mapped port position.
Ports are available, if you look and plan around the popular ones (such
as UARTs, soundblasters, CD-ROM cards, etc.).  You'll want to make it
configurable to several possible ports.  This design assures that each
random byte can only be read once.  A TSR couldn't read the card in
parallel (because reading a port doesn't require hooking an interrupt),
so the only way to compromise it is to subvert the application reading
the card.  Conventional anti-virus protection can see to it that the app
remains trustworthy.

> Cypherpunks write code (or maybe work on hardware :-) !

I hack both.  Hardware is fun!
- -- 
Roy M. Silvernail --  roy@sendai.cybrspc.mn.org will do just fine, thanks.
          "Does that not fit in with your plans?"
                      -- Mr Wiggen, of Ironside and Malone (Monty Python)
        PGP 2.3a public key available upon request (send yours)

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