1. Center for Information Security Technologies, Korea University Digital Image Steganalysis Kwang-Soo Lee

2. Outline Steganography LSB Steganography LSB Steganalysis

3. Cryptography Cryptography scrambles a message to obscure its meaning. Today secure communication is often identified with cryptography. However, cryptography reveals the fact that communication is happening. ??? @2*$#d(*%7*

4. Steganography The word “steganography” comes from Greek, steganos and graphein. Steganography is the art of hiding information in ordinary-looking objects. Steganography aims to conceal the existence of secret communication.

5. Classical Steganography Examples: Hidden tattoo, Covered writing, Invisible ink, Microdots, Character arrangement, Paper mask, etc. Hiding a secret message in physical objects. Secrecy depends on keeping the methods secret.

6. Modern Steganography Hiding information in digital objects, Invisibly. The Invisibility must depend on just the stego-key, not the stego system.

7. LSB Steganography Replacing least-significant-bits (LSBs) of digital data with message bits. Using digital multimedia, such as image, audio, video, as cover-objects. Embedding random message bits in LSBs will not cause any discernable difference from the cover-signals. Easy to implement, High payloads. 11001000 Extracting Embedding

8. Digital Images for Steganography Types of digital images: binary, gray-scale, RGB color, palette, JPEG, etc. The LSB plane of image data looks like random noise. Bit-plane decomposition of the Lena image in gray-scale. lena.bmp6 th Bit Plane4 th Bit PlaneLSB Plane

9. LSB Steganalysis Steganalysis is the science of detecting hidden messages in digital signals. It takes advantage of statistical or perceptual distinction of stego-signals from cover-signals. LSB steganalysis Visual attack, histogram analysis (PoV analysis), Closed color analysis, Regular-singular (RS) analysis, Sample pair (SP) analysis, LR Cube analysis, Etc.

10. PoV analysis Proposed by Westfeld and Pfizmann (IH 1999). PoV means a pair of values which differ just in the LSBs. 0 1 2 3 4 5 6 7 8 9 10 …… LSB embedding tends to equalize those frequencies of the values of each PoV. cover-image histogram stego-image histogram LSB Embedding

11. Sample Pair Analysis Proposed by Dumitrescu et al. (IH 2003) Based on symmetry of quantized noise distribution. Take advantage of spatial correlation such as pixel adjacency. Estimate the length of hidden message. Outperform PoV analysis. cover-image histogram stego-image histogram LSB Embedding

12. LR Cube Analysis Left and Right cube analysis (LRCA), developed by us (IH 2005) Our method uses high dim. vectors as basic units drawn from digital signals. Consider the vector noise distribution and its distortion of LSB embedding.

13. LR Cube Analysis Left cube and Right cube, and the possible cube patterns or complexities. Cover-signals show similar complex levels between the left cubes and the right cubes, but these are not the case for stego-signals after the LSB embedding LRCA works by measuring the similarities between these two distributions.

14. Center for Information Security Technologies, Korea University Thank you Kwang-Soo Lee kslee@cist.korea.ac.kr