Stego-SIRDSStego-SIRDS

William L. Bahn

CS-591 Project

07 December 2005

A Common Steganographic TechniqueA Common Steganographic Technique

Use a 24-bit image fileUse a 24-bit image file Strip 1 or 2 LSB’s from each byteStrip 1 or 2 LSB’s from each byte Replace with the Stego-dataReplace with the Stego-data

How to embed the buried data?How to embed the buried data?

As part of the fundamental image.As part of the fundamental image. Use data source as random number source.Use data source as random number source. Mark non-random pixels.Mark non-random pixels. Between 20% and 75% of pixels are random.Between 20% and 75% of pixels are random. Fill factors of up to 60% to 70% achievable.Fill factors of up to 60% to 70% achievable.

Full pixel replacementFull pixel replacement Use some agreed upon selection function.Use some agreed upon selection function. Fill factors of 25% to 33% achievable. Fill factors of 25% to 33% achievable.

The typical way – LSB replacement.The typical way – LSB replacement. Random data – fill factors of 87.5% achievable.Random data – fill factors of 87.5% achievable. Raw data – fill factors of 50% to 75% achievable.Raw data – fill factors of 50% to 75% achievable.

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

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

Normal image at 50% fillNormal image at 50% fill

Unmodified Cover ImageUnmodified Cover Image Stego-image w / 50% fillStego-image w / 50% fill

Normal image at 75% reverse fillNormal image at 75% reverse fill

Unmodified Cover ImageUnmodified Cover Image Stego-image w / 75% rev fillStego-image w / 75% rev fill

Unmodified SIRDS imageUnmodified SIRDS image

Strong stereo image even with only the most significant bit retained!

Strong stereo image even with only the most significant bit retained!

Unmodified Cover ImageUnmodified Cover Image Stego-image w / 87.5% fillStego-image w / 87.5% fill

BUT….BUT….

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

Even side by side it isn’t too obviousEven side by side it isn’t too obvious

Unmodified Cover ImageUnmodified Cover Image Stego-image w / 50% fillStego-image w / 50% fill

So what does it hide?So what does it hide?

Stego-image w / 50% fillStego-image w / 50% fill My house!My house!

87.5% fill is a waste of time87.5% fill is a waste of time

Unmodified Cover ImageUnmodified Cover Image Stego-image w / 87.5% fillStego-image w / 87.5% fill

75% fill has obvious artifacts - very difficult to view stereo-image

75% fill has obvious artifacts - very difficult to view stereo-image

Unmodified Cover ImageUnmodified Cover Image Stego-image w / 75% fillStego-image w / 75% fill

75% reverse fill shows minor artifacts but is viewable as a stereo image

75% reverse fill shows minor artifacts but is viewable as a stereo image

Stego-image w / 75% rev fillStego-image w / 75% rev fillUnmodified Cover ImageUnmodified Cover Image