Re: [WM]: What is different bewteen watermarking and steganography

[Hans Georg Schaathun <georg+wmlist@ii.uib.no>]

On Fri, Feb 24, 2006 at 06:49:21PM -0800, huynh hoc wrote:
>   I am confusing about the terminology "watermarking" and 
> "steganography". Could you help me to classify these terminology. What is different bewteen watermarking and steganography?

There is probably more than one answer to this, but this is mine.
Please be invited to criticise.

Steganography is used for the following scenario:
  Alice wants to send a secret message to Bob, without
  Eve's knowing that there is a secret message.
  (This is usually obtained by hiding the secret message
  in an innocent message, but this is not important for the
  concept of steganography.)

[Cryptography:
  Alice wants to send a secret message to Bob, without
  Eve's knowing what the secret message is.
  (She is allowed to know that there is secret communications
  though.)
]

Robust watermarking:
  Alice want to send a information message coupled with a host
  message, in such a way that Bob (or anyone else) is not able
  to retransmit a message similar to the host without also
  retransmitting the information.  (The information is not
  necessarily secret.)

Fragile watermarking:
  Alice wants to send an information message coupled with a host
  message, in such a way that Bob (or anyone else) is not able
  to retransmit a modified message similar to the host while
  retaining the information.

Obviously, watermarking is more than one thing; these to are not the only ones.  My own background is in security/cryptography,
where steganography is fairly well-defined for a couple of millenia.
Watermarking covers many different things, which are widely different from a security perspective.


-- 
:-- Hans Georg                             http://www.ii.uib.no/~georg/

`This Universe never did make sense; I suspect that it was built
on government contract.'                                     (Heinlein)


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