[Cryptography] cheap sources of entropy

[ianG]

On 20/01/14 20:54 PM, Krisztián Pintér wrote:
> 
> 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.


Indeed.  I should mention that the context was the key creation ceremony
where I could monitor the situation.  I don't see it as a general solution.

iang