[Cryptography] cheap sources of entropy

[Krisztián Pintér]

ianG (at Saturday, January 18, 2014, 9:17:17 AM):

> 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

collecting entropy is easy. extracting entropy is also easy. providing
a general solution that reliably produces entropy is hard. just as an
example, take this camera project. the following questions come up,
from the top of my head:

- what if the camera breaks?
- what if the camera entropy production degrades with time?
- what if lighting conditions change?
- what if the driver is updated, and starts filtering noise?
- what if the driver is updated, and stops producing data?
- what if temperature variations affect entropy production?
- what if an attacker can listen on in EM, and read your camera output?
- what if another software on the same machine can read camera output?
- what if the janitor accidentally unplugs the camera?

in short: if you have an engineer, some free hours to spend, and you
want to generate some randomness at a certain location, with a
specific hardware, in a specific setting, it is always easy to do. but
these solutions do not transfer to different situations, and does not
apply to anyone with no engineer hours to spend.