植基於有意義的分享影像之像素非擴展式視覺密碼技術

Pixel Unexpanded Visual Cryptography Techniques Based on Meaningful Shadows

蔡欣儀(Hsin-Yi Tsai)

指導教授 ： 張真誠

國立清華大學/電機資訊學院/資訊系統與應用研究所/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00064

摘要

傳統的機密分享機制中，機密資訊將利用複雜的數學運算方法來產生兩個以上無意義的share。然而，此方法在解碼過程中將浪費大量時間與運算能力。而後，視覺密碼學的產生將用來解決傳統機密分享方法在解密與加密的過程中浪費大量運算時間的缺點。此方法可利用人類視覺系統來回復原始影像，進而改善計算時間的浪費。然而此方法有項重大缺失，在於原始影像大小上會因此擴展，將導致於在攜帶性與儲存上的困難。而且所產生的無意義share並非安全，在傳輸的過程中亦有機會遭受攻擊者的注意，且在辨認上將產生管理上的困難。因此，避免上述的問題以及保護機密資訊是項重要的議題。
因而在本論文中我們提出了兩個user-friendly且無擴展影像的機密分享方法。在第一個方法中結合了多項式機密影像分享機制(PISS)與視覺機密影像分享機制(VSS)進而產生有意義的share，使得機密影像不僅可利用人類視覺機制預先瀏覽影像，且可以無失真的方法完整回復原始影像。而為了藏入更多的機密資訊，在第二個方法中，我們預先設計一個像素無擴展式的編碼簿，利用此編碼簿將兩張機密影像編碼成兩張有意義的share。而且根據不同的旋轉角度，兩張機密影像可以同時的藏入兩張share中。並且在解密的過程當中，我們將根據不同的旋轉角度以利用疊合的技巧來堆疊兩張share，進而萃取出兩張藏入的機密影像。然而，此方法有個顯著的特點在於疊合的結果中可完整的呈現原始影像中的黑色像素點，使得影像可以清楚的被辨識。

關鍵字

視覺機密分享 ； 預覽影像 ； 無擴展影像 ； 驗證機制

並列摘要

Traditional secret sharing scheme which encrypts secret image based on mathematical calculation to construct two or more shares that often requires the complicated computation to extract secret. Later on, conventional visual cryptography scheme was developed to deal with the perplexed calculation in encryption and extraction of previous schemes. The stack-to-see technique can be used easily to reveal the secret by human visual system, which can shorten computation time. However, the expansion of image size and the noise-liked shares of previous schemes lead to the difficulty in transmission and storage. Moreover, the noise-liked shares are insecure which may attract the attention of eavesdroppers and also difficult to identify and manage. To prevent above problems and protect the security of secret information is an important issue.
Thus, this study proposes two schemes of user-friendly and unexpanded secret sharing mechanism. The first scheme with two decoding options based on polynomial based image secret sharing (PISS) and Visual secret sharing (VSS) scheme. The scheme is to generate the user-friendly shares and offer a previewing result of the secret image according to the stacking operation, while it can retrieve a lossless secret image. To embed more confidential information, the second scheme uses a pre-defined codebook to encode two secret images into two meaningful shares without pixel expansion. According to the turning mechanism, two secret images can be embedded into two shares simultaneously. The decryption process allows the user to get two secrets via turning and stacking. A notable feature of our scheme is that the black pixel value of the secret image can be completely extracted and the vision quality of stacking results can be identified clearly.

並列關鍵字

Visual secret sharing ； preview ； user-friendly ； unexpanded ； authentication

參考文獻

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