[Cryptography] cheap sources of entropy

[Peter Gutmann]

ianG <iang at iang.org> writes:

>Jon Callas (I think) a long time ago suggested pointing your cheapo USB
>camera at a photographer's grey card in low light.  The theory is that the
>cells in a camera seek for information and if they don't see something that
>is worth reporting, it drives them a little tipsy.  The claim is that this
>effect can drive them into some form of quantum uncertainty.

... unless your camera, or the driver software, is doing postprocessing to 
remove noise.  If you're using a DSLR for this then you can just force it to 
return data in raw mode, but with anything else you have no idea how much 
noise is being removed by aggressive postprocessing.  Or, more importantly, 
whether a future software update won't change things so that your currently 
nicely noisy image is de-noised.

So by all means point your camera out the window at the leaves of a tree or
something similar, but don't rely on noise from a static image like a test
card.

Peter.