In a non-readable form using certain algorithms and

In modern day environment, security of data is a major concern in data transmission. Thus there is a need of a system that can ensure the security of our data in a network during transmission. Cryptoystem is one of such systems. The information is converted from a readable form to a non-readable form using certain algorithms and processes at the sender side in secured communication. Encryption and Decryption are among the techniques and procedures used to transmit information securely over he network. Thus encryptio and decryption makes it possible for sending information over an insecure network to the desination 4.
Initially Naor and Shamir proposed use of a secret shariig approach in 1979. Lagrange’s theorem of Polynomial Interpolation was the basis of Shamir’s secret sharing scheme. The data which is a sercret image is divided into $n$ number of shares $share1, share2, share3,…, share n$ and then these n shared are copied onto n transparencies and then are distributed among n members each recieving one share such that (i) atleast k shares are required among total n shares to reveal the secret information. (ii) less than k shares reveal no information about secret image. This technique is also known as (k,n) threshold secret sharing. The (k,n) secret sharing scheme is based on the principle that minimium k points are necessary to define a polynomial of degree (k-1) 5.
Another seccret sharing scheme was proposed by G. blakley and A. Shamir in 1979.Hyper Plane Geometery was the basis of their secret sharing scheme. They used the principle that the intersection of non-parallel line is a single specific point. Main points of this secret sharing scheme are (i) secre is a single point in m dimentional space. (ii) There is a hyper plane corresponing to a share. (iii)Secret is the intersection of the certain amount of planes called threshold planes. (iv) Secret is not revealed if planes are less than threshold planes 6.
In 1983, Asmuth and Bloom proposed another secret shaing scheme. They used Chiinese Remaindr Theorem as the basis of their sheme. In their scheme, they used reduction modulo opration. The recovery of secret is done using system of congurance with the help of Chines Remainder theorem 7.
Initially visual cryptography was use only on binary images. This lead to it becomeing inefficient in real time usage.
A new method of visual cryptography was proposed by Chang-ChouLin and Wen-Hsiang Tsai for grey scale images. It makes the use of dithering techniques. All the grey scale images are used to convert to their approximate binary sclae images using a dithering technique. Then the existing cryptographic schemes for binary images is applied to that image to generate shares. But all the generated shares look like noisy images. They are raandom patterns. They carry no visual imformation. This is one of the limitations of his scheme. But even when the number of bits in each pixel increses to 256 there is a satisfactory increase in size of image and its decoded quality 8.
Zhi Zhou, Gonzalo R. Arce, and Giovanni Di Crescenzo proposed model of Halftone Visual Cryptography. Abstract Visual cryptography encodes a secret binary image (SI) into n shares of random binary patterns. If the shares are xeroxed onto transparencies, the secret image can be visually decoded by superimposing a qualified subset of transparencies, but no secret information can be obtained from the superposition of a forbidden subset. The binary patterns of the n shares, however, have no visual meaning and hinder the objectives of visual cryptography. Extended visual cryptography was proposed to construct meaningful binary images as shares using hypergraph colourings, but the visual quality is poor 9.