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