分享機密影像於多張影像之改進方法

IMPROVED METHODS FOR SHARING A SECRET IMAGE IN MULTIPLE IMAGES

曾泳承(Yung-Cheng Tseng)

指導教授 ： 汪順祥

大同大學/電機資訊學院/電機工程學系所/碩士(2009年)

摘要

資訊安全領域中有一種和過去傳統密碼技術加解密方式不同，稱為資訊隱藏技術[1]，顧名思義就是一種將需要隱藏的資訊給藏入，讓人無法很輕易的去發現的技術。如此，確保了其資訊的安全性。
資訊隱藏技術中有一種稱為視覺密碼技術，此技術不需要靠電腦去計算，因為沒有繁瑣的計算式，只要用人的視覺系統透過顏色的對比方式和投影片的疊合,就可以將隱藏的資訊給辨識出來，此為Noar 和Shamir [3] 在1994提出的一門新的學問，稱為視覺密碼學(Visual Crypthography) 。
但由於視覺密碼技術運用上，其圖形像素上幾乎都是黑色和白色，因此不論在偽裝圖形上或是偽裝圖形投影片疊合還原回機密資訊，其圖形顏色表現都只限於黑色或是白色。所以衍生出彩色視覺密碼，加入色彩，讓圖形變的更活潑，也比較更融入人們中的生活。雖然是如此，但並不是每種彩色視覺密碼的編碼方式都能讓偽裝圖形以及偽裝圖形所疊合的資訊能貼近原圖原色。在文獻[2]中，由於其圖形偽裝後的偽裝圖效果並不是很好，且圖片也變大3X3，也就是圖形尺寸放大9倍，本論文就是根據原來的演算法提出幾個改進方法，去使偽裝圖形更貼近原掩護圖形，尺寸也縮小，由原來的3X3倍變成2X2倍，縮小放大比例。

關鍵字

顏色空間-YIQ

並列摘要

In the field of information security, there is a category of technology called Information Hiding Technique [1] which encrypts and decrypts in different ways from the traditional encryption technology in the past. It is based on the behavior of hiding secret information , thus ensure the security.
One of the Information Hiding Techniques, called Visual Cryptography proposed by [3] Noar and Shamir in 1994, does not need computer calculation because it has no complicated calculation formula. We can decode the hidden information by color contrast and superimposing shares which consist of a transparency through human visual system.
In the original Visual Cryptography, the pixels of the image are almost composed of black and white. Consequently, whether in the cover images of separated shares or images reconstructed by superimposing shares, the color performance is restricted to black and white. As a result, color visual cryptography was then developed. Adding colors makes images more vivid and closer to people’s life.
It is found that not every coding manner can precisely depict the original colors of encrypted or reconstructed images. In [2] it proposed a good algorithm to share a secret gray image in Multiple images. However, the outcome of camouflage image is not satisfactory, and the picture is also enlarged to 3×3, which is 9 times bigger than the original image size. This thesis is to improve this algorithm to make the camouflage images more similar to the original cover images, and reduce the size enlarged from 3×3 to 2×2, so as to decrease the zoom ratio.

並列關鍵字

YIQ

參考文獻

[7] 張智星，MATLAB程式設計與應用，2版，新竹市，清蔚科技股份有限公司，民89，11月，4-16、6-19頁。

[2] C. C. Chang and T. X. Yu, “ Sharing a secret gray image in multiple images,” Proceedings of the First International Symposium on Cyber Worlds, pp.230-237, 2002.

[3] M. Naor and A. Shamir, “ Visual Cryptography,” Advances in Cryptology-Eurocrypt '94, Lecture Notes in Computer Science, vol. 950, pp. 1-12, 1995.

[9] 侯永昌，張兆源，林芳助，以半色調技術製作彩色視覺密碼，資管評論，第十期，民89，12月，22-38頁。

[1] 張真誠、黃國峰、陳同孝，電子影像技術，旗標出版股份有限公司，初版，台北，民92，8月，295-309頁。