Simple inner transposition steganography

[Peter Wayner]

At 4:01 PM -0400 9/18/03, Victor.Duchovni at morganstanley.com wrote:
>On Thu, 18 Sep 2003, edo wrote:
>
>>  Maybe it works as a very, very weak form of encryption, one which can
>>  be decrypted at a glance by humans but would evade the most simplistic
>>  computer recognition systems.  But stego it ain't.
>>
>
>Steganography is in the eye of the beholder.

Very nice line.

I have to agree. There are always two channels in steganography and 
its cousin watermarking. You want to make changes in one channel so 
the other channel isn't affected. In this case, a munged word doesn't 
affect the human reader but it can carry log_2(n!) bits where n=count 
of non-duplicate letters - 2. So we have two channels.

Now, I will admit that a large number of munged words will trigger 
something in the human, but it's entirely possible that three or four 
munged words on a page WON'T EVEN BE NOTICED. Believe me. I've proof 
read books a number of times and it's surprising how much gets 
through even the best copy editors.

Three or four words per page is also enough to insert more than a few 
bits of watermarking. A seven letter word can carry almost seven 
bits. So let's call it 6 bits. If you change four seven letter words 
on a page, you've 24 bits. Not bad.



-Peter


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