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Stego-SIRDS William L. Bahn CS-591 Project 07 December 2005
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A Common Steganographic Technique Use a 24-bit image file Strip 1 or 2 LSB’s from each byte Replace with the Stego-data
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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.
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2-bit Stego-Image (25% fill factor) (taken from Wikipedia)
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Normal image at 50% fill Unmodified Cover Image Stego-image w / 50% fill
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Normal image at 75% reverse fill Unmodified Cover Image Stego-image w / 75% rev fill
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Unmodified SIRDS image
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Strong stereo image even with only the most significant bit retained! Unmodified Cover Image Stego-image w / 87.5% fill
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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!
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Even side by side it isn’t too obvious Unmodified Cover Image Stego-image w / 50% fill
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So what does it hide? Stego-image w / 50% fill My house!
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87.5% fill is a waste of time Unmodified Cover Image Stego-image w / 87.5% fill
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75% fill has obvious artifacts - very difficult to view stereo-image Unmodified Cover Image Stego-image w / 75% fill
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75% reverse fill shows minor artifacts but is viewable as a stereo image Stego-image w / 75% rev fill Unmodified Cover Image
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