VCPSS ： A two-in-one two-decoding-options image sharing method combining visual cryptography (VC) and polynomial-style sharing (PSS) approaches Sian-Jheng Lin, Ja-Chen Lin Pattern Recognition Society, 2007 指導老師：李南逸 Speaker ： Tzu-Chen Huang 1

Outline Introduction Visual cryptography PSS Encoding Decoding Conclusion 2

Introduction If the decoding computer is temporarily not available, we can stack to get a vague black- and-white view of the secret image. The computer is finally available, we can get a much finer gray-valued view of the secret image using the information hidden earlier in the shadows. 3

Visual cryptography Input: An integer threshold t, and an integer n (t ≦ n). Output: A pair of basis matrices [B0] and [B1] 4

Visual cryptography 5

PSS To share an image by Thien and Lin’s sharing scheme 6

SSecret image HHalftone binary version of the image S Compressed version of S Shadows Transparency LTable L which has entries. wWhite elements bBlack elements tGet the shared secret in n transparencies KA security key nProduced n transparencies 7

Encoding The flowchart to summarize the idea of encoding 1 8

Encoding Input :S,L,K Output:  Step 1. Compressed S obtain a  Step 2. Use K to encrypt  Step 3. create 9

Encoding Step 4. S transformed the halftone version (H). Step 5. H is created to Step 6. Partition the S to n regions (S/n block) Step 7. 10

Decoding The flowchart of the decoding algorithm. 11

Decoding of stacking Input ： Any t of the n transparencies, L Output ： H  Step 1. Stack all t collected transparencies to get an enlarged H.  Step 2. By counting black/white elements of each block, we get H. 12

Decoding of extraction Input ： Any t of the n transparencies, L,K Output ：  Step 1. Extract the hidden in region I of the i) Use L inspecting the |S|/n blocks in region i of  Step 2. Get of the n shadows i) is a digit string of |S|/n, and each digit is in ii) each digit string from base  Step 3. Recover (encrypted) from the t shadows { } i) Using the inverse processing of the PSS ii) Recover the t coefficients { }  Step 4. Decrypt by K  Step 5. Get the gray-value secret image 13

Conclusion Proposed a new method which combines two major branches of image sharing. In the decoding issue, this new method is more flexible than applying VC or PSS. 14

2007/8/29 meeting 再找看看有沒有更新的 Paper 來看 (2007 年 ) 。 15