Visual cryptography

About: Visual cryptography is a research topic. Over the lifetime, 1724 publications have been published within this topic receiving 25300 citations.

New Colored Visual Secret Sharing Schemes

Abstract: Visual secret sharing (VSS) schemes are used to protect the visual secret by sending n transparencies to different participants so that k-1 or fewer of them have no information about the original image, but the image can be seen by stacking k or more transparencies. However, the revealed secret image of a conventional VSS scheme is just black and white. The colored k out of n VSS scheme sharing a colored image is first introduced by Verheul and Van Tilborg [1]. In this paper, a new construction for the colored VSS scheme is proposed. This scheme can be easily implemented on basis of a black & white VSS scheme and get much better block length than the Verheul-Van Tilborg scheme.

Visual Cryptography II: Improving the Contrast Via the Cover Base

Abstract: In Eurocrypt 1994 we proposed a a new type of cryptographic scheme, which can decode concealed images without any cryptographic computations, by placing two transparencies on top of each other and using the decoder's (human) visual systems. One of the drawback of that proposal was a loss in contrast: a black pixel is translated in the reconstruction into a black region, but a white pixel is translated into a grey region (half black and half white). In this paper we propose am alternative model for reconstruction with a different set of operation (which we call the “Cover” semi-group) is proposed. In this model we are able to obtain a better contrast than is possible in the previous one.

Improved Schemes for Visual Cryptography

Abstract: A (k,n)-threshold visual cryptography scheme ((k,n)-threshold VCS, for short) is a method to encode a secret image SI into n shadow images called shares such that any k or more shares enable the “visual” recovery of the secret image, but by inspecting less than k shares one cannot gain any information on the secret image. The “visual” recovery consists of xeroxing the shares onto transparencies, and then stacking them. Any k shares will reveal the secret image without any cryptographic computation. In this paper we analyze visual cryptography schemes in which the reconstruction of black pixels is perfect, that is, all the subpixels associated to a black pixel are black. For any value of k and n, where 2\leq k\leq n, we give a construction for (k,n)-threshold VCS which improves on the best previously known constructions with respect to the pixel expansion (i.e., the number of subpixels each pixel of the original image is encoded into). We also provide a construction for coloured (2,n)-threshold VCS and for coloured (n,n)-threshold VCS. Both constructions improve on the best previously known constructions with respect to the pixel expansion.

Embedded Extended Visual Cryptography Schemes

Abstract: A visual cryptography scheme (VCS) is a kind of secret sharing scheme which allows the encoding of a secret image into n shares distributed to n participants. The beauty of such a scheme is that a set of qualified participants is able to recover the secret image without any cryptographic knowledge and computation devices. An extended visual cryptography scheme (EVCS) is a kind of VCS which consists of meaningful shares (compared to the random shares of traditional VCS). In this paper, we propose a construction of EVCS which is realized by embedding random shares into meaningful covering shares, and we call it the embedded EVCS. Experimental results compare some of the well-known EVCSs proposed in recent years systematically, and show that the proposed embedded EVCS has competitive visual quality compared with many of the well-known EVCSs in the literature. In addition, it has many specific advantages against these well-known EVCSs, respectively.