臺灣博碩士論文加值系統

視覺機密分享(Visual Secret Sharing, VSS)是對影像進行加密的技術，其主要的精神是，解密時不需要透過任何的計算，只須使用人類的視覺系統(Human Visual System)就可以還原出原始的資訊。此外，視覺機密分享繼承了機密分享(Secret Sharing)的優點。概念是將一張機密影像加密成多張無意義的分享影像(Share)，參與分享的人都各持有一張分享影像，唯有疊合適當的分享影像才能還原出原始秘密訊息。

隨機網格(Random Grid)是視覺機密分享機制的一種技術，它的優點是不需建置密碼簿，產生出來的分享影像與原來的機密影像大小一樣，是一個簡單且低成本的技術。然而當實際把兩張分享影像疊合時，會有精準對齊的困難。

因此本研究提出了利用隨機網格方法，在不擴張像素的條件下，對機密影像做加密後得到兩張隨機影像，且在疊合兩張隨機影像時，即使沒有完全正疊，在其中一張平移(Shifting)或斜移(Diagonal Shifting)時，仍可還原機密影像達到可容錯的機制。如此可使視覺機密配置系統更具實用性。

Visual secret sharing(VSS) is a technology of image encryption, which does not requir any calculation at the time of decryption, just alone with the human visual system then the secret can be recovered. The concept of VSS is encrypting a secret image into two meaningless shares. We can only decrypt the secret image by stacking these shares together. Random grid, which is a skill for making a visual secret sharing scheme, the advantage is that it does not need the codebooks, and the size of each share will be the same size as the secret image. It is a simple and useful technique to share secret image. However, there would be problems in alignment when these two shares are staked by hand in practical. Therefore, this thesis presents the fault-tolerant schemes when stacking two shares that are acquired from secret image encryption without pixel expansion. When two shares are stacked, even without been perfectly stacked, we can restore the image to achieve fault-tolerant. Both theoretical analysis and simulation results demonstrate the effectiveness and practicality of the proposed schemes.

致謝I
論文摘要III
Abstract IV
Table of Contents V
List of Figures VII
List of Tables VIII
1 Introduction 1
2 Related Work 3
2.1 Visual Cryptography Concepts . . . . . . . . . . . . . . . . . . . . 3
2.2 Random Grid Encryption Algorithm . . . . . . . . . . . . . . . . 5
2.3 The Main Idea of Nakajima and Yamaguchi Scheme . . . . . . . . 8
2.4 The MTVSS Scheme . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 The Proposed Schemes 11
3.1 The Main Idea and Algorithm . . . . . . . . . . . . . . . . . . . . 11
3.2 The Experimental Results . . . . . . . . . . . . . . . . . . . . . . 17
4 Analysis and Comparison 22
4.1 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.2 Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5 Conclusion 45
References 46
Appendix 48

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