From: "Alexander 'Sasha' Chislenko" <sasha1@netcom.com>
Date: Sun, 10 Mar 1996 12:16:09 +0800
To: cypherpunks@toad.com (Cypherpunks mailing list)
Subject: Stego - images and sounds
Message-ID: <2.2.32.19960310030830.00ec2fc8@netcom.com>
MIME-Version: 1.0
Content-Type: text/plain


At 12:19 PM 3/8/96 -0800, Jim McCoy <mccoy@communities.com> wrote:
>
>Provided the bits are random in the way that they should be... The low-order
>bits in such files were chosen by implementors of stego programs because
>modification would not be noticed by the person viewing or listening to
>the file, not necessarily because there was actually randomness at this
>level which could be replaced.  Does anyone know of a survey of images or
>sound files which tested the statistical randomness of these bits?  They
>may not be as random as people think they are.
>

 This should depend on how the image/sound was obtained, though I am pretty
sure in most cases there would be easily detectable patterns.  They would
be the strongest in software-generated files, smaller in good reproductions
of precise recordings, and very small in noisy recordings.  In all cases,
the number of lower bits used for stego-messages may be chosen lower than
the existing noise of the signal.  Changing all lower bits in a good
rendered image may still be unnoticeable for the human viewer, but really
easy to detect to a program.

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Alexander Chislenko <sasha1@netcom.com>
Home:      http://www.lucifer.com/~sasha/home.html
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