[Cryptography] cheap sources of entropy

Jerry Leichter leichter at lrw.com
Mon Jan 20 11:45:49 EST 2014


On Jan 19, 2014, at 8:04 PM, "Christian Huitema" <huitema at huitema.net> wrote:
> [I]f the camera truly delivers the pixels that it sees, I
> wonder why I would rely specifically on pointing at a grey card. Simply
> pointing at a landscape or an interior scene will probably provide just as
> much entropy. Minute differences in the location and orientation of the
> camera will cause pixels to shift. In a handheld device like a cell phone,
> we can ask the user to take a series of pictures while randomly moving the
> phone. Hashing  the images will certainly deliver some pretty  good input to
> the entropy bucket.
Getting quality random bits when you have (a) almost any kind of high-rate real-world sensor and (b) a human being willing to help is an easy problem.  Any modern cellphone can provide tons of randomness if a person moves it around, talks to it, waves his hands around in front of it.  (The bigger challenge is making sure the software in the cellphone doesn't either strip away or "leak" all that fine randomness.)
                                                        -- Jerry

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