1. An Innovative Steganographic Scheme Based on Vector Quantization
Chin-Chen Chang
Chair Professor, Feng Chia University
Honorary and Hopewell Appointed Professor, National Chung Cheng University
Hopewell Appointed Professor, National Tsing Hua University

2. Introduction Images have been widely used in our daily life.
The image security has become an important issue in current computer world.
Image cryptology is a very useful tool to defend the information security.
2019/2/17

3. Apply the Traditional Cryptosystem on Images
Cipher Image
Original Image
Decrypted Image
encryption
decryption
2019/2/17

4. Problems The cipherimage is meaningless. Image Camouflage
Image size is huge
Image Compression
The decrypted image containing a small distortion is usually acceptable.
Vector Quantization
2019/2/17

5. Virtual Image Cryptosystem
Original Image
Advantages:
camouflage
security
compression
acceleration
Decrypted Image
Cipher Image
Virtual Image
2019/2/17
encryption
decryption

6. VQ Encoding Index table Original Image Codebook
(120,155,…,80) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
(90,135,…,120)
(100,125,…,150) …
Index table
Original Image
(49,117,…,25)
(50,42,…,98)
(20,65,…,110)
Codebook
2019/2/17
How to get a good codebook?

7. LBG Algorithm Step 1: Training Images Training vectors setx0 x1 .
Dividing the images into vectors
x59997
X59998
x59999
Training Images
Training vectors set
2019/2/17

8. LBG Algorithm Step 2: Initial codebook Training vectors setx0 X1 .
x73
x342 .
Randomly choose 256 initial code-vectors
256 code-
vectors
x24312
x49810
x59997
x59998
x59999
Initial codebook
Training vectors set
2019/2/17

9. The set of training vectors = {x0, x1, … , x59999}
LBG Algorithm
Step 3:
Vector-groups 1 . x0 X1 .
{x5, x5431, … }
{x1, x306, … }
{x67, x822, … }
. . .
254
255
x59997
x59998
x59999
Codebook
The set of training vectors = {x0, x1, … , x59999}
Join the closest code-vectors, and to form 256 vector-groups.
2019/2/17

10. LBG Algorithm Step 4: Vector-groups {x5, x5431, …} {x1, x306, … }1 .
254
255
{x5, x5431, …}
{x1, x306, … }
{x67, x822, …}
. . .
Compute mean value of each group,
replace the old code-vectors
New Codebook
Go to Step3 to repeat training until the total distortion has stabilized.
Chang, C. C. and Lin, C. Y., (2007): "Density-Based Image Vector Quantization Using a Genetic Algorithm," The Proceedings of 13th International MultiMedia Modelling Conference (MMM2007), (Cham, T. J., Cai, J., Dorai, C., Rajan, D., Chua, T. S. and Chia, L. T. Eds.), Springer Verlag, Part I, Singapore, Jan. 2007, pp
2019/2/17

11. The Principle of the Virtual Image Cryptosystem
Separate O into a set of vectors {O1, O2, O3,…, Ono}.
Separate V into another set of vectors {V1, V2, V3, … , Vnv}.
Let O be the original image.
Let {V1, V2, V3, …, Vnv} be the codebook.
2019/2/17

12. Encryption
Randomly generate the transformed-origin G and the project-direction D.
Project {V1, V2, V3, …, Vnv} to D based on G.
Sort the projected results, and obtain {V’1, V’2, V’3, …, V’nv}.
2019/2/17

13. 2019/2/17

14. Hide wc, hc, noc, Gc, Dc, and Ic into the pixels of V.
Encrypt w, h, no, G, and D into wc, hc, noc, Gc, and Dc by DES-like, respectively.
Encrypt I into Ic, where Ic=IXORX and X is the bit-string containing G, D, G, D,… only.
Hide wc, hc, noc, Gc, Dc, and Ic into the pixels of V.
Cipher Image Vc
2019/2/17

15. Decryption
2019/2/17

16. Empirical Tests-Test 1
Original Image
Airplane
512 X 512
2019/2/17

17. Empirical Tests-Test 1 Virtual Image Lena 256 X 256 Cipher Image Lena
PSNR=37.87dB
2019/2/17

18. Empirical Tests-Test 1 Decrypted Image Airplane 512 X 512 PSNR=30.22dB
2019/2/17

19. Empirical Tests-Test 2
Original Image
Airplane
512 X 512
2019/2/17

20. Empirical Tests-Test 2 Virtual Image Cipher Image Lena Lena 360 X 360
PSNR=45.13dB
2019/2/17

21. Decrypted Image Airplane
Empirical Tests-Test 2
Decrypted Image Airplane
512 X 512
PSNR=31.36dB
2019/2/17

22. Original Image Peppers
Empirical Tests-Test 3
Original Image Peppers
512 X 512
2019/2/17

23. Empirical Tests-Test 3 Cipher Image Virtual Image Lena Lena 256 X 256
PSNR=37.60dB
2019/2/17

24. Empirical Tests-Test 3 Decrypted Image Peppers 512 X 512 PSNR=29.91dB
2019/2/17