Hu Chih-Ming, Tzeng Wen-Guey
Department of Computer Science, National Chiao-Tung University, Hsinchu, Taiwan 30050, R.O.C.
IEEE Trans Image Process. 2007 Jan;16(1):36-45. doi: 10.1109/tip.2006.884916.
Visual cryptography (VC) is a method of encrypting a secret image into shares such that stacking a sufficient number of shares reveals the secret image. Shares are usually presented in transparencies. Each participant holds a transparency. Most of the previous research work on VC focuses on improving two parameters: pixel expansion and contrast. In this paper, we studied the cheating problem in VC and extended VC. We considered the attacks of malicious adversaries who may deviate from the scheme in any way. We presented three cheating methods and applied them on attacking existent VC or extended VC schemes. We improved one cheat-preventing scheme. We proposed a generic method that converts a VCS to another VCS that has the property of cheating prevention. The overhead of the conversion is near optimal in both contrast degression and pixel expansion.
可视密码术（VC）是一种将秘密图像加密成共享图像的方法，使得堆叠足够数量的共享图像就能揭示出秘密图像。共享图像通常以透明片的形式呈现。每个参与者持有一张透明片。之前关于可视密码术的大多数研究工作都集中在改进两个参数：像素扩展和对比度。在本文中，我们研究了可视密码术中的作弊问题以及扩展的可视密码术。我们考虑了恶意对手可能以任何方式偏离该方案的攻击。我们提出了三种作弊方法，并将它们应用于攻击现有的可视密码术或扩展的可视密码术方案。我们改进了一种防作弊方案。我们提出了一种通用方法，可将一个可视密码术方案转换为另一个具有防作弊特性的可视密码术方案。在对比度下降和像素扩展方面，转换的开销几乎是最优的。
