[11146] in cryptography@c2.net mail archive
Re: Maybe no stego on eBay afterall
daemon@ATHENA.MIT.EDU (Peter Wayner)
Fri Jul 19 16:25:25 2002
In-Reply-To: <p05111701b95e076ce166@[207.172.123.55]>
Date: Fri, 19 Jul 2002 16:14:12 -0400
To: Jon Simon <jon@jonsimon.com>, cryptography@wasabisystems.com
From: Peter Wayner <pcw2@flyzone.com>
At 11:18 AM -0700 7/19/02, Jon Simon wrote:
>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?
Yup. You can see my book, _Disappearing Cryptography_, for any
complicated mechanism for creating arbitrarily complex data.
-Peter
http://www.wayner.org/books/discrypt2/
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