# [Cryptography] The ultimate random source

Phillip Hallam-Baker hallam at gmail.com
Sat Feb 15 23:46:00 EST 2014

```On Sat, Feb 15, 2014 at 11:22 PM, Arnold Reinhold <agr at me.com> wrote:

> On Thu, Feb 13, 2014 at 8:08 PM, Joseph Ashwood <ashwood at msn.com> wrote:
>
>
> From: Phillip Hallam-Baker
>
> I have a solution to the random number generator problem that can be
>
> built for about \$50 and is completely verifiable.
> [shake a flask of candy, take a picture]
>
>
> I'm not confident it will have as much entropy as you think. The design is
> a fairly basic modification of the lavarand design.
>
>
> Put aside the question of camera digitization noise and just consider the
> random placement of discrete objects in the camera's scene. For simplicity
> replace the flask with a flat bottom box, such as a shoe box, and maybe
> rectangular candies, small compared to the box. Standard machine vision
> algorithms can measure the edges, and hence position and orientation of
> such objects to sub-pixel precision, easily one part per thousand in X, Y,
> and Theta with a megapixel camera. We don't have to make the measurements,
> just know the information is in the image. That's 30 bits per object,
> assuming the objects are all visually distinct.  (If the objects
> are identical visually, subtract log2(10!), or about 22 bits.) And then
> there is the position and orientation of the camera, which can also be
> calculated from the image. So a photo of ten different objects, randomly
> placed should easily produce at least 256-bits of entropy before even
> considering other information in the image.
>
>
That was my conclusion.

I actually started with rather more elaborate steampunk devices that had
dice with different colored faces. These would be machine read somehow.

Then in the next iteration I had a grid of the dice being read at once.

Then I realized that I could read them with a camera.

Then I replaced the dice with colored balls.

I hadn't seen lavarand back in the day, but I had the idea after finding
one while looking for the flask to put the m&ms in...

What got me started on this course is that I don't like trusting the
assumed lack of bias in very small measurements. That is not repeatable or
measurable or auditable. I want to see devices that I can check and know
are functioning right.

Adding a camera to a Raspberry Pi is \$40 which is a lot less than almost
any custom circuit is going to be.

--
Website: http://hallambaker.com/
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