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 http://filter.cs.ccu.edu.tw
CCC
Vector Quantization (VQ) Concept Encoding and Decoding
Vector Quantization (VQ) Image compression technique Image w h Index table Vector Quantization Encoder
標準向量量化編碼法
Original image (512*512 pixels) 機密影像 機密影像 (64*64 pixels) Original image (512*512 pixels)
找出相近的Pairs
發現 d(CW0, CW8) > TH d(CW13, CW14) > TH 藏 1 藏 0 CW1 CW11 ,CW2 Unused CW0, CW8, CW13, CW14
4 4 Encode Unused CW0, CW8, CW13, CW14 Index Table Image Index Table
Secret message 1 0 1 0 1 0 0 1 0 1 1 1 1 0 0 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
Secret message: 1 0 1 0 1 0 0 1 0 1 1 1 1 0 0 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
Secret message: 1 0 1 0 1 0 0 1 0 1 1 1 1 0 0 1 1 1 1 1 1 1 1 Index Table Secret message
隱像術
隱像術 Introduction Virtual Image Cryptosystem Empirical Tests
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.
Apply the Traditional Cryptosystem on Images encryption decryption Original Image Cipher Image Decrypted Image
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)
Virtual Image Cryptosystem Advantages: Camousflage Security Compression Acceleration Original Image Decrypted Image Virtual Image encryption decryption Cipher Image
Vector Quantization Encoder w VQ encoder h Codeword i k i ‧‧‧‧‧‧ ‧ ‧ Compressed Data (indices) Codebook Original Image
Vector Quantization Decoder w VQ decoder h Codeword i k i ‧‧‧‧‧‧ ‧ ‧ Compressed Data (indices) Codebook Decompressed image
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.
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}.
Encryption (cont.) VQ encoder w h Codeword i i Relationship I k V’3 i ‧‧‧‧‧‧ ‧ ‧ Relationship I between O and V V’nV Codebook Virtual Image V Original Image O
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
Decryption VQ Decoder w h Codeword i i Relationship I between O and V k V’3 i ‧‧‧‧‧‧ ‧ ‧ Relationship I between O and V V’nV Codebook Virtual Image V Original Image O
Original Image Airplane Empirical Tests Test1: Original Image Airplane 512X512
Virtual Image Lena 256X256 Cipher Image Lena 256X256 PSNR=37.87 dB
Decrypted Image Airplane 512X512 PSNR=30.22 dB
Original Image Airplane Test2: Original Image Airplane 512X512
Virtual Image Lena 360X360 Cipher Image Lena 360X360 PSNR=45.13 dB
Decrypted Image Airplane 512X512 PSNR=30.22 dB
Original Image Peppers Test 3: Original Image Peppers 512X512
Virtual Image Lena 256X256 Cipher Image Lena 256X256 PSNR=37.60 dB
Decrypted Image Peppers 512X512 PSNR=29.91 dB
Original Image Peppers Test 4: Original Image Peppers 512X512
Virtual Image Boat 256X256 Cipher Image Boat 256X256 PSNR=37.74 dB
Decrypted Image Peppers 512X512 PSNR=30.31 dB
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.
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.