1. Stego-SIRDS William L. Bahn CS-591 Project 07 December 2005

2. A Common Steganographic Technique  Use a 24-bit image file  Strip 1 or 2 LSB’s from each byte  Replace with the Stego-data

3. How to embed the buried data?  As part of the fundamental image.  Use data source as random number source.  Mark non-random pixels.  Between 20% and 75% of pixels are random.  Fill factors of up to 60% to 70% achievable.  Full pixel replacement  Use some agreed upon selection function.  Fill factors of 25% to 33% achievable.  The typical way – LSB replacement.  Random data – fill factors of 87.5% achievable.  Raw data – fill factors of 50% to 75% achievable.

4. 2-bit Stego-Image (25% fill factor) (taken from Wikipedia)

5. Normal image at 50% fill Unmodified Cover Image Stego-image w / 50% fill

6. Normal image at 75% reverse fill Unmodified Cover Image Stego-image w / 75% rev fill

7. Unmodified SIRDS image

8. Strong stereo image even with only the most significant bit retained! Unmodified Cover Image Stego-image w / 87.5% fill

9. BUT….  Prior image used pseudorandom buried data.  Use of encryption/compression can randomize data.  Random buried data can sometime ease analysis.  But this is not the case here - the “R’ in SIRDS!

10. Even side by side it isn’t too obvious Unmodified Cover Image Stego-image w / 50% fill

11. So what does it hide? Stego-image w / 50% fill My house!

12. 87.5% fill is a waste of time Unmodified Cover Image Stego-image w / 87.5% fill

13. 75% fill has obvious artifacts - very difficult to view stereo-image Unmodified Cover Image Stego-image w / 75% fill

14. 75% reverse fill shows minor artifacts but is viewable as a stereo image Stego-image w / 75% rev fill Unmodified Cover Image