Re: Against TEMPEST

From: Guy Macon (http://www.guymacon.com)
Date: 06/18/04 

Date: Fri, 18 Jun 2004 05:20:18 -0700

Mok-Kong Shen <mok-kong.shen@t-online.de> says...
>
>Guy Macon <http://www.guymacon.com> wrote:
>
>> Mok-Kong Shen <mok-kong.shen@t-online.de> says...
>>
>>>Guy Macon <http://www.guymacon.com> wrote:
>>>
>>>>Why bother with Enigma-style encryption? I can build an RC4
>>>>encryption device that runs on fluid power - no electricity
>>>>- and can even add the "discard the first 256 outputs" and
>>>>"discard 15 out of every 16 outputs" modifications. Nobody
>>>>has shown any practical method of attacking such a system, so
>>>>adding another computer-based encryption level would just be
>>>>icing on the cake.
>>>
>>>I think user comfort is essential. You could try to build
>>>a prototype of your RC4 device and see how that works.
>>>(I intuitively quite doubt its practicality.)
>>
>> It would be expensive (two valves per bit plus a couple of hundred
>> valves for counters, etc. but anyone who has designed fluid power
>> logic will tell you that it's a straightforward engineering exercise
>> that any first-year student cuold do. All of the functions needed
>> (memory, selectors, XOR, etc.) were worked out long ago - all you
>> need to do is to string them together.
>
>Where do you get the power to drive the fluid?

A tank of compressed air is traditional.

>I guess (as layman) that the size of the apparatus will at
>least likely to be larger than an modern version of machine
>of Enigma kind

Yes. An Enigma (electric or pneumatic) could be built that is the
size of a D-Cell battery plus whatever you need for keyboard and
display. The thousand or so valves needed to do RC4 would take up
a cube 0.5 meters on a side - about as big as the original Enigma.
Then again, an Enigma code is easily broken.

>and the maintenace might be more troublesome.

Not really. Pneumatic valves are very, very reliable. I would
expect more trouble with the custom rotors that an Enigam would
require.

>What's wrong with electro-mechanical devices, if TEMPEST
>isn't an issue?

They are several orders of magnitude less reliable, more
expensive and slower than a microcontroller. 

-- 
Guy Macon, Electronics Engineer & Project Manager for hire. 
Remember Doc Brown from the _Back to the Future_ movies? Do you 
have an "impossible" engineering project that only someone like 
Doc Brown can solve?  My resume is at http://www.guymacon.com/