[149136] in cryptography@c2.net mail archive
Re: [Cryptography] cheap sources of entropy
daemon@ATHENA.MIT.EDU (=?iso-8859-15?Q?Kriszti=E1n_Pint=E)
Mon Jan 20 12:57:42 2014
X-Original-To: cryptography@metzdowd.com
Date: Mon, 20 Jan 2014 18:54:03 +0100
From: =?iso-8859-15?Q?Kriszti=E1n_Pint=E9r?= <pinterkr@gmail.com>
To: ianG <iang@iang.org>
In-Reply-To: <52DA388D.8040708@iang.org>
Cc: cryptography@metzdowd.com
Errors-To: cryptography-bounces+crypto.discuss=bloom-picayune.mit.edu@metzdowd.com
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.
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