From: Sergey Goldgaber <sergey@delbruck.pharm.sunysb.edu>
Date: Mon, 28 Feb 94 21:56:34 PST
To: Norman Hardy <norm@netcom.com>
Subject: Re: standard for steganography?
In-Reply-To: <199403010523.VAA00389@mail.netcom.com>
Message-ID: <Pine.3.89.9403010051.A12975-0100000@delbruck.pharm.sunysb.edu>
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On Mon, 28 Feb 1994, Norman Hardy wrote:

> Has anyone done statistical studies of low bits of pixels or sound samples?
> I suspect that they are often far from random. A flat 50% distribution in
> the low bits might standout like a sore thumb. I can imagine the the low
> bit can be distributed dependently on such things as the next to low bits
> or 60 cycle power at the recorder. Some AD converters are known to produce
> 60% ones or some such.  Like mechanical typewriters, AD systems probably
> have there own idiosyncrasies. Given a flat stream of cipher data, there
> are techniques to reversably introduce such variations to mimic the biases
> of real AD converters without much data expansion.
> 
> It is my wild guess and conjecture that with such statistical variation
> built in there would be no effective statistical test for a given file
> containing hidden messages.
> 
> 

Yes, pure white noise would be anamalous.  I have suggested that one use 
a Mimic function with a "garbage grammar".  Implemented correctly, it should
withstand statistical analysis.

What is an AD converter?  And what are the techniques you speak of that 
mimic those AD converters?


Sergey