From: jim@bilbo.suite.com (Jim Miller)
Date: Sun, 6 Mar 94 16:17:41 PST
To: cypherpunks@toad.com
Subject: Re: some technical steganography
Message-ID: <9403070012.AA20650@bilbo.suite.com>
MIME-Version: 1.0
Content-Type: text/plain



>
>> I assert that an "unrecognizable encrypted message" will be a 

>> random sequence of bits.  Is my assertion correct?  

>
> It's neither correct or incorrect because the specific
> notion of randomness hasn't been specified.
>

I don't understand what you mean by "specific notion of randomness  
hasn't been specified".  How many different "notions of randomness"  
are there?


> Your statement is falsifiable, however, since
> sometimes a non-random string of bits is what you want to
> get out, if what you would expect to get out normally was
> also non-random.  And you want them to be non-random in the
> same way. 

> 


I agree.  The output of the reverse stego process should produce  
similar results, regardless of the presence of a hidden message.   
That's the point I've been trying to make.  I've been attempting to  
make that point by describing a hypothetical stego system that, when  
run in reverse, produces a random sequence of bits.  I suppose there  
could be other hypothetical stego systems that produce non-random  
output, but then you would need a decryption system that could  
understand and decrypted that non-random output.  I prefer random bit  
sequences.  Or perhaps I should say - bit sequences with no apparent  
structure.


> > Of course, this assumes there is no other way to detect a
> > hidden message besides reversing the stego process and
> > testing the result. 

> > 

> 

> Don't count on it.  Statistical tests can find
> correlations you hadn't suspected were there.  In fact,
> for some message types, _not_ finding the correlations
> may indicate dithering, or maybe a steganographic
> message. 

> 


I agree completely.   This is a large part of what makes effective  
steganography so difficult to achieve.


Jim_Miller@suite.com