[Cryptography] Best internet crypto clock: hmmmmm...

Tom Mitchell mitch at niftyegg.com
Mon Oct 27 21:14:32 EDT 2014

On Sun, Oct 26, 2014 at 6:22 AM, <dan at geer.org> wrote:

> > Here's Balasubramaniyan's PhD thesis describing the Pindr0p technology:
> >
> >
> https://smartech.gatech.edu/bitstream/handle/1853/44920/balasubramaniyan_vijay_a_201108_phd.pdf
> Along similar lines, small noise in image acquisition is now well
> enough understood and discernible to say "This camera did take that
> picture" as it does to say "This rifle did fire that bullet," which
> extends to "These two pictures/bullets came from the same camera/rifle."
How much of that image survives the conversion to a JPG compressed image.
At a RAW level this makes sense but RAW is very uncommon and most
of the raw formats are vendor specific.  EXIF data can be edited...

Extraction of noise from image data would be helped a lot by knowing
about the image source.  An opaque cover might be enough but would require
local physical activity.   Noise in a white image and noise in a black
image would
likely be very different.

Images of clouds (like lava lamps) or leaves on trees  would prove
difficult to correlate
well enough to understand noise.

Of interest Nikon went through a recall on their D600 camera where
splatters of lubrication
were showing up on the sensor over time.   Sensors (shutters) were replaced
and cleaned.  Also
the more expensive Nikon permit saving a reference image to help remove
noise and also
calibrate white balance.  The reference dust image changes with time enough
that it is
not a factory installed reference.

For images I am not convinced.   It is just too easy for a bad guy to scuff
an image
in difficult to detect ways.  To my knowledge there is nothing kin to the
dot code of copiers and printers in camera sensors (yet).  Printers good
enough to
worry the counterfeit folk early on were expensive enough to be engineered
cell phone image sensors and image software  has no budget room to make
hiding easy.

  T o m    M i t c h e l l
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