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Physical Key Encryption

Secret screen overlay decoder
  [vote for,

However complicated software-based encryption gets, however long the keys, sooner or later the message is translated on a computer. If that computer or its screen has been hacked - someone is monitoring the house voltage, for example, and using that to interpret the screen image - then the value of all that encryption has just evaporated.

So let's go back to good, old-fashioned physical keys: now, you will be provided with a unique screen overlay, consisting of a plastic film covered with colored and opaque dots and tiny mirrors. The message will be embedded in an image which will only be clear when viewed on your particular screen model through your personal overlay. Sort of like Enigma for pictures.

Now the image is only interpreted outside the receiving computer, and the only way for someone to crack it is to look over your shoulder.

The application might need to use the keyboard arrow keys to nudge the image on the screen to line up exactly with the reference marks.

It would probably work best if it came in a box of wheaties, possibly in ring format.

dalek, Jan 20 2003

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       To provide any useful security, each overlay would have to be used once only. Reuse of an overlay would very easily allow the material encrypted with it to be decoded.   

       Still, an interesting notion. It's possible to use a graphical overlay to implement a one time pad; as such, if the overlay is only used once and is not compromised the security is absolute.
supercat, Jan 21 2003

       I seem to remember a product for sending encrypted faxes that worked something like this.
krelnik, Jan 21 2003

       Hardly: no overlay is involved, and you are entering secret data, not reading it.
dalek, Mar 04 2003

       Baked and gone stale. I remember copy protection for 80's-era games that used this scheme. It wasn't much fun, trying to line up the mesh.   

       Also I would be very surprised if what you described was not provably mathematically equivalent to encryption; in this case using a 2d matrix.   

       As described it would also be immediately vulnerable to a known-plaintext attack, unless the decryption key was used as a one-time pad; a very specialised application.   

       Also, I just upgraded to a 22" monitor, from a 20". This scheme would break.
koshua, Nov 29 2003


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