Shaped like a big old fashioned magnifying
glass that Sherlock Holmes would be
proud to own.
You move the device over the document
and read the unencrypted plain-text.
So: you set up a PGP private/public key
pair. Encrypt a standard document using
your public key.
Software converts
the encrypted bytes to a
rectangular bit-map format : probably
would have to contain some extra
positional data. (Labeling smaller areas
within the large bit map with x,y coords).
The "Magnifying glass" is actually a
scanner on one side and an LCD display on
the other.
First, hold the magnifying glass over the
entire bitmap, then scan over sections -
the text appearing on the display. Purely
for effect, it could magnify the text as you
moved in and out of the document.....
This device has no real actual real-world
use that I can think, but it hold a certain
novelty value - perhaps a child's toy.
It could come with a crooked pipe with a
big fat glowing red LED in the end whose
brightness varied when you 'dragged on'
the pipe.
And a hat with flappy bits on this side.
(Perhaps motorized-flaps, so you could
emote 'aha!' moments when you
discovered a clue etc).