Maybe no stego on eBay afterall

Peter Wayner pcw2 at flyzone.com
Fri Jul 19 16:14:12 EDT 2002


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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