I've done some thinking about how this image signing device would have
to work. My guess is that the special compact flash card has two extra
things:
* A co-processor to compute the encryption
* A hidden secret "key" unique to that card
The card computes a signature Y based on the image and the key:
Y = f(image,key)
and stores it in the file header.
Even if the algorithm (f) is known and you have large numbers of image and
signature pairs there is no way to find the key better than brute force if
your algorithm is cryptographicaly "strong". The keys are probably at least
64 bits long, and likely much longer.
The verification software would copy an image file to the card and compare a
newly computed signature with the one stored in the image header.
--
Warren Marts <[EMAIL PROTECTED]> -- Socorro, NM, USA
Lover of travel, languages, good beer/wine, and anything with a motor
"There's two kinds of fools: one says 'This is old, and therefore good,'
and the other says 'This is new, and therefore better.'" - John Brunner
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