## Visual Cryptography Research Paper

Visual cryptography allows to encrypt information that is available in the form of white and black pixels. The decryption can be done only by using the optical perception, in particular the help of computers required.

To write a successful research paper on the topic you should know that visual cryptography visual cryptography was first introduced Moni Naor and Adi Shamir in 1994. It was used to encrypt the image or the text presented in the form of images. The basic idea of the visual cryptography model was to break the original image into a plurality of encrypted images (or shadow images), each of which would give no information about the original image except maybe its size (image – a la “white noise”). When superimposing the encrypted images, the original image can be obtained. Thus, the decoding does not require special knowledge, HPC and even computer (if shadow images are printed on transparencies).

When using this algorithm in computer systems, to superimpose all the images on top of each other, the logical operations AND, OR, XOR (or setting a high degree of transparency in the graphical editor) can use. This technology gas a high degree of crypto-protection due to the fact that dividing the original image into a plurality of shadow images occurs randomly. Such technology can find application in copy protection and authentication (copyright, watermarking), tracking of electronic forms for remote voting, encryption, financial documents, key management access, and sharing passwords.

Naor and Shamir demonstrated (k, n)-visual secret sharing scheme, where the image was divided into n parts so that anyone who had any k parts could decrypt it, while any k-1 pieces did not give any information about the contents of the original image. When all k parts will be superimposed on each other, we can see the original image. To divide the original black-and-white image into n parts, each pixel is represented as a number of smaller parts (subpixels). The number of white and black pieces is always the same. If the pixel is divided into two parts, it turns out, one white and one black block. If a pixel is divided into four equal parts, we get two white and two black blocks.

Each pixel of the original image will be split into four parts, so if the size of the original image was M × N, then the size of the shadow image will be 2M × 2N. The figure shows that the pixel is divided into four parts, can have six different states. If Pixels on the first layer has a single position, the pixel on the second layer in turn may have two positions: either identical inverted pixel of the first layer. If a pixel of the pixel portion 2 is identical to 1, the pixel obtained by superimposing both the shadow image is half white and half black. Such pixel is called gray or blank. If the pixels are Part 1 and Part 2 are opposite, the pixel, the resulting overlay is completely black.

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