YASS: Yet Another Steganographic ScHeme that Resists Blind Steganalysis

1. YASS: Yet Another SteganographicScHemethat Resists Blind Steganalysis Solanki et. Al Presented by Yamin Noor

2. Steganography - Historical Notes • Demaratus sent a warning about a forthcoming attack to Greece by writing it directly on the wooden backing of a wax tablet before applying its beeswax surface. • Histiaeus shaved the head of his most trusted slave and tattooed a message on it. After his hair had grown the message was hidden. The purpose was to instigate a revolt against the Persians.

3. Steganography - Now • Used for secured communication of secret message. • Hidden in digital images (host/cover). • Hidden message cannot be detected by statistical or perceptual analysis of Stego/Composite image. • Must be recoverable by receiver even after distortion.

4. Example of Steganography

5. Example of Steganography

6. Digital Image Steganography • JPEG is the most popular format. • Most methods hide data in the LSB of the quantized DCT coefficients of the image. • Hiding image in specific region or the whole image changes the histogram of DCT coefficient. • Steganalyzers can compare the histogram of DCT coefficients of the host and the stego. • Good steganography should yield stego with DCT coefficent histogram closest to that of the host.

7. Blind Steganalysis • Unavailability of the host image. • Approximate host image from the stego(self-calibration). • Better steganography need to be able to resist self-calibration. • Authors claimed that YASS can resist self-calibration and, thereby, resist blind steganlysis.

8. Recap • There will be difference in features between host and stego. • Steganlysists need host image or a good approximate of host image to find such differences. • Resisting the steganlysists from approximating the host image makes the steganography undecodable.

9. YASS • Implements randomized hiding of data. • No consistent assumption about the hiding process can be made. • Host image features cannot be reliably estimated.

10. Implementation of YASS N M

11. Implementation of YASS N M B B

12. Implementation of YASS N M 8x8 8x8 8x8 8x8 B B

13. Implementation of YASS N M 8x8 8x8 8x8 8x8 B B

14. Implementation of YASS N M B B

15. Implementation of YASS N M B B

16. Repeat-Accumulate Code • JPEG Compression can cause erroneous decoding by the receiver. • Repeat-Accumulate Code is an algorithm that can reduce error during JPEG compression through an iterative algorithm.

17. Performance of YASS • Embedding Capacity • Detection probability

18. Embedding Rate • Embedding rate or capacity is the number of bits that can be hidden in an host using a steganographic algorithm. • Embedding rate of YASS depends on • JPEG Quantizer Factors QFaand QFh • Dimension of Big Block Size B

19. JPEG Quantizer Factors

20. Dimension of B

21. Detection of YASS • Training a support vector machine (SVM) • Xo = Actual Host Image • X1 = Actual Stego Image • Yo = Observed Host Image • Y1 = Observed Stego Image

22. Detection of YASS • Farid – 72 dimensional vector based • PF-23 – 23 dimensional DCT based • PF-274 – 274 dimensional DCT and Markov based • DCT Histogram – Histogram of DCT Coeff • Xuan-39 – Spatial domain steganalysis • Chen-234 – JPEG Steganlysis

23. Detection of YAS

24. Trade-offs in YASS QFa- QFh QFa- QFh Embedding Capacity Steganalysis Performance

25. Trade-offs in YASS Big Block Dimension Big Block Dimension Embedding Capacity Steganalysis Performance

26. YASS vs. Other Steganography

27. Conclusion • YASS provides more security than other methods against blind steganlysis. • Randomly chosen blocks confuses staganlysists and reduces the consistency of steganlysis algorithm. • There is a real-estate cost for YASS, i.e. the number of bits that can be stored is less than other methods.

28. Questions ?