[51889] in Cypherpunks
Re: Stego - images and sounds
daemon@ATHENA.MIT.EDU (E. ALLEN SMITH)
Sun Mar 10 21:03:18 1996
Date: Sun, 10 Mar 1996 20:46 EDT
From: "E. ALLEN SMITH" <EALLENSMITH@ocelot.Rutgers.EDU>
To: sasha1@netcom.com
Cc: cypherpunks@toad.com
X-Envelope-To: cypherpunks@toad.com
X-Vms-To: IN%"sasha1@netcom.com"
From: IN%"sasha1@netcom.com" "Alexander 'Sasha' Chislenko" 9-MAR-1996 22:59:54.01
>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.
Unless the picture, sound, whatever has a periodic function, the LSB
ought to have an approximately random distribution (barring all 0's and all
1's, for full color saturation). The periodic function part could be a problem.
-Allen
