Information-Theoretic Analysis of Information Hiding

[David Honig]

At 12:30 AM 7/15/03 -0400, Don Davis wrote:
>"An electrical engineer at Washington University
> in St. Louis has devised a theory that sets the
> limits for the amount of data that can be hidden
> in a system and then provides guidelines for how
> to store data and decode it. Contrarily, the
> theory also provides guidelines for how an
> adversary would disrupt the hidden information.

"But the theory answers the questions, what is the optimal attack.."

There are ways of preventing any modification (attack) of the
carrier.  E.g., sign the carrier (with the private
half of a widely published public key).  Although this
technique would attract attention until widespread.

Note that Disney has to do this as well as Osama,
lest someone post Disney content, with the "not ok to copy freely"
watermark mutated.  Otherwise a downloader would
protest, "but the file said it was free, and the
included-file-hash said it was intact!"  (Because
the mutator also provided a new hash.)

(Disney's situation is worse, of course, because 
even the pristine, Disney-signed content is copyable at the
analog (etc) level.  And Osama can use multiple images as carriers
for a single message.)






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