[11143] in cryptography@c2.net mail archive
Re: Maybe no stego on eBay afterall
daemon@ATHENA.MIT.EDU (Jon Simon)
Fri Jul 19 16:02:19 2002
In-Reply-To: <E17Vc2C-00022m-00@smtp10.atl.mindspring.net>
Date: Fri, 19 Jul 2002 11:18:20 -0700
To: cryptography@wasabisystems.com
From: Jon Simon <jon@jonsimon.com>
At 1:55 PM -0400 7/19/02, Peter Wayner wrote:
>The basic scheme is very simple. Generally the inserted message has
>higher entropy than the raw LSBs of an image. So the entropy of the
>picture/message combo should be higher than the picture alone. So
>you look at the entropy and choose all images that pass a threshold.
>You can do better by using your understanding of normal images to
>create more sophisticated statistics. But there's little you can do
>about large images and small messages. As the proportion of changed
>pixels drops, the statistics end up closer and closer to the norm.
If this is the case, then wouldn't a thorough stego program filter
the image post hiding to lower the entropy, making searching by this
method far less useful than its already sad state?
-Jon Simon
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