[Cryptography] True RNG: elementary particle noise sensed with surprisingly simple electronics

[Bill Cox]

The noise you are describing is called "thermal noise", and is ensured to
be there by basic physics.  You have discovered the method used by
"Turbid".  I reviewed their system a while back:

http://www.metzdowd.com/pipermail/cryptography/2014-October/023417.html

Looking at my review, I don't think I gave them enough credit early enough
for doing the basic research on this TRNG method.  It really is excellent
work.  That said, I agree with a lot of Bear's comments, such as using
simple devices, and even the glitter nail polish.

Bill

On Thu, Sep 15, 2016 at 12:34 PM, Thierry Moreau <
thierry.moreau at connotech.com> wrote:

> Hi!
>
> A true random number generation strategy is no better than its
> trustworthiness. Here is a suggestion for a simple scheme which rests on a
> common digital electronic design.
>
> While helping an undergrad student in a weight scale project, I
> encountered an A-to-D conversion circuit datasheet where some fundamental
> noise was explicitly quantified.
>
> After a little research, I learned that a foremost unavoidable noise
> source is resistor "current noise" (i.e. occurring due to an elementary
> physics phenomenon):
>
> <citation>
> Thick-film resistors are made of a mixture of conductive particles
> (metallic grains) with a glassy binder and an organic fluid. This “ink” is
> printed on a ceramic substrate and heated in an oven. During this firing
> process the conductive particles within the glassy matrix are fused to the
> substrate and form the resistor.
>
> [All types of resistors] have in common that the total noise can be
> divided into thermal noise and excess noise. Excess current noise is the
> bunching and releasing of electrons associated with current flow, e.g. due
> to fluctuating conductivity based on imperfect contacts within the
> resistive material. The amount of current-noise depends largely on the
> resistor technology employed.
>
> [T]hick film resistors show large excess noise.
> <citation/>
>
> Source: Frank Seifert, "Resistor Current Noise Measurements," April 14,
> 2009
>
> The classical weight scale design is based on an 24 bits A-to-D (analog to
> digital) conversion with the sensing circuit made of a wheatstone bridge (a
> simple resistor network arrangement) that amplifies minute variations in
> individual resistor voltage caused by strain gauge deformation (a small
> directional stress on a strain gauge induce a change in resistor value).
> The basic idea of turning this classical design into a true noise sensing
> application is this one: replace the (minutely) variable resistor by a
> fixed resistor with a high noise level.
>
> The surprisingly simple electronics is illustrated by two A-to-D
> integrated circuits (Avia Semiconductor HX711 and Texas Instrument ADS1232)
> and the open hardware design for a weight scale microprocessor board
> (SparkFun OpenScale).
>
> Obviously the evil is in the details, and some refinements are desirable
> since a) the noise sensing application is better served with a larger
> signal amplification, and b) the confidence in the noise sampling approach
> is (presumably) raised if noise sources other than current noise are
> reduced with appropriate circuit design techniques. But none of this is
> rocket science (e.g. compared with other elementary physics noise sampling
> such as so-called quantum noise generators).
>
> Unavoidable current noise source:
>  - thermal noise
>  - excess current noise caused by the above resistor material construction
> Noise sources to be reduced (as a matter of sampling approach coherency)
>  - electrostatic ...
>  - electromagnetic ...
>
> Any thoughts?
>
> Regards,
>
> - Thierry Moreau
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