The Basic Model Of Visual Cryptography And The Extended Model

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Visual Cryptography is a type of cryptographic scheme used to encode a secret image into shadow images called shares or layers such that it can’t be decrypted using the human visual system unless certain qualified subsets of the shares are used. The secret image is encoded without the use of any cryptographic computations. In this paper we will discuss the basic model of visual cryptography and the extended model; using the k out of n scheme.
Keywords: Visual Cryptography, Extended Visual Cryptography. 1. Introduction
Secret sharing is a scheme that permits a secret message to be shared among a set P of n participants. The secret is shared in such a way that only qualified subsets of P can recover the secret, any nonqualified subset has no information on the secret. We take into consideration, the problem of encrypting pictures and printed texts such that it is perfectly secure without the hassle of using cryptographic computations. In 1979, Shamir [7] and Blakley [8] introduced the concept of a threshold scheme. A (k, n) threshold scheme is a method whereby n pieces of information of a secret key k, called shares are distributed among n participants so that the k cannot be re constructed from the knowledge of fewer than k shares. In 1995 Naor and Shamir [1] proposed a new type of cryptographic scheme, which could encode and decode secret images without any cryptographic computations. The reason this scheme was considered remarkable was that the secret message

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