1. 資訊偽裝術 張真誠 講座教授 多媒體暨網路安全實驗室 http://www.cs.ccu.edu.tw/~ccc

2. CCC

3. Vector Quantization (VQ) Concept Encoding and Decoding

4. Vector Quantization (VQ)
Image compression technique
Image w h
Index table
Vector Quantization Encoder

6. 標準向量量化編碼法

7. Original image (512*512 pixels)
機密影像
機密影像 (64*64 pixels)
Original image (512*512 pixels)

8. 找出相近的Pairs

9. 發現 d(CW0, CW8) > TH d(CW13, CW14) > TH 藏 1 藏 0 CW1 CW11 ,CW2
Unused
CW0, CW8, CW13, CW14

10. 4 4
Encode
Unused
CW0, CW8, CW13, CW14
Index Table
Image
Index Table

11. Secret message 1 1 1 1 1 1 1 1
Index Table
Secret message
CW1, CW2,
CW4, CW5
CW6, CW7
CW11, CW3
CW15, CW10
CW12, CW9
藏 1
藏 0

12. Secret message: 1 1 1 1 1 1 1 1
Index Table
Secret message
CW1, CW2,
CW4, CW5
CW6, CW7
CW11, CW3
CW15, CW10
CW12, CW9
藏 1
藏 0

13. Secret message: 1 1 1 1 1 1 1 1
Index Table
Secret message

14. 隱像術

15. 隱像術
Introduction
Virtual Image Cryptosystem
Empirical Tests

16. 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.

17. Apply the Traditional Cryptosystem on Images
encryption
decryption
Original Image
Cipher Image
Decrypted Image

18. Problems The cipherimage is meaningless. Image size is huge.
Image Camouflage(影像偽裝)
Image size is huge.
Image Compression(影像壓縮)
The decrypted image containing a small distortion is usually acceptable.
Vector Quantization(向量量化編碼法)

19. Virtual Image Cryptosystem
Advantages:
Camousflage
Security
Compression
Acceleration
Original Image
Decrypted Image
Virtual Image
encryption
decryption
Cipher Image

20. Vector Quantization Encoderw
VQ encoder h
Codeword i k i
‧‧‧‧‧‧ ‧ ‧
Compressed Data
(indices)
Codebook
Original Image

21. Vector Quantization Decoderw
VQ decoder h
Codeword i k i
‧‧‧‧‧‧ ‧ ‧
Compressed Data
(indices)
Codebook
Decompressed image

22. 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.

23. 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}.

24. Encryption (cont.) VQ encoder w h Codeword i i Relationship Ik
V’3 i
‧‧‧‧‧‧ ‧ ‧
Relationship I
between O and V
V’nV
Codebook
Virtual Image V
Original Image O

25. Encryption (cont.)
Encrypt w, h, no, G, and D into wc, hc, noc, Gc, and Dc by DES-like, respectively.
Encrypt I into Ic, Where Ic=IXOR X 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

26. Decryption VQ Decoder w h Codeword i i Relationship I between O and Vk
V’3 i
‧‧‧‧‧‧ ‧ ‧
Relationship I
between O and V
V’nV
Codebook
Virtual Image V
Original Image O

27. Original Image Airplane
Empirical Tests
Test1:
Original Image Airplane
512X512

28. Virtual Image
Lena
256X256
Cipher Image
Lena
256X256
PSNR=37.87 dB

29. Decrypted Image Airplane
512X512
PSNR=30.22 dB

30. Original Image Airplane
Test2:
Original Image Airplane
512X512

31. Virtual Image
Lena
360X360
Cipher Image
Lena
360X360
PSNR=45.13 dB

32. Decrypted Image Airplane
512X512
PSNR=30.22 dB

33. Original Image Peppers
Test 3:
Original Image Peppers
512X512

34. Virtual Image
Lena
256X256
Cipher Image
Lena
256X256
PSNR=37.60 dB

35. Decrypted Image Peppers
512X512
PSNR=29.91 dB

36. Original Image Peppers
Test 4:
Original Image Peppers
512X512

37. Virtual Image
Boat
256X256
Cipher Image
Boat
256X256
PSNR=37.74 dB

38. Decrypted Image Peppers
512X512
PSNR=30.31 dB

39. Security Analyses
The camouflage is the first safeguard of our cryptosystem.
Suppose the illegal users detect that the virtual image is fake:
We have proven that none can break our cryptosystem by any attack.

40. Conclusions The advantages of our image cryptosystem:
Camousflage
Security
Compression
Acceleration
This image cryptosystem is suitable for all applications of images; such as printer, scanner, and camera.