10-10-2014, 11:03 AM
A PUZZLE-BASED DEFENSE STRATEGY AGAINST
FLOODING ATTACKS USING GAME THEORY
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Abstract
– Now – a – days, many mechanisms are developed to solve the denial – of – service attacks caused by users in networks. This denial – of – service attacks are caused by flooding. All the developed mechanisms are not solving the problems of effectiveness and optimality. To solve this problem, in the paper we are proposing the game theory strategy. Security is very important in recent years in networking. Networking plays an important role in our daily activities.
INTRODUCTION
PRE-PROCESSING HALFTONE IMAGES
The applying of visual cryptography to grey scale pictures by 1st changing the photographs to a binary image employing a halftoning algorithmic program. The task of the project is to implement an algorithm, which should be fast and the printed images must look good based, on human visual perception. In this project, we survey some of the existing methods. Further, based on 2-by-2 block replacement method, we propose an improved algorithm. The improvements can be divided into three major parts. They are:
1. Adaptive gray level region definition
2. Inclusion of the nearest neighbours in the analysis before halftoning
3. Parallelize the algorithm in order to speed up the conversion.
WHAT IS HALFTONING AND HOW IT WORKS
AN IMPROVED PRE-PROCESSING SCHEME
Block replacement halftoning is a commonly used halftoning technique. In this method each pixel in the original image is replaced by one of the defined set of binary blocks. The dimension of the patterns is determined by screen frequency and the print resolution [1]. For simplicity, assume that each pixel is going to be replaced by a 2X2 matrix. Since the dimension of the matrix is 2X2 then only five different gray levels can be represented by the set of matrices, see Fig 3. The pixel belong to one of the five gray level regions is replaced by the corresponding predetermined candidate. Fig 3 illustrates how this method works. In this illustration only the representation for the first and the last pixel are shown. The same is done for the rest of the original image. In Fig 2 the left is the image halftoned by a 2-by-2 block replacement halftoning, and the right is by a 3-by-3 block replacement. The 3-by-3 block replacement can represent ten different gray levels. Comparing the two images (a) and (b), we see that the 3-by-3 block replacement can keep more details than 2-by-2 replacement, the bigger number of gray levels, the higher resolution. In contrast to the ordered dithering method, the arrangement of the black micro dots in the patterns does not have necessarily to be clustered or to be dispersed. Due to the low-pass spatial frequency property of the human eye, the same gray level can be represent by two different patterns, any of which can possibly be arranged as a clustered dot and another as a dispersed dot. The choice of the patterns has an impact on the characteristics of the final halftoning image. This will be describes in detail in the next section.
VISUAL SECRET SHARING SCHEME:
The basic model of the visual cryptography consists of a several number of visible sheets. On every visibility a cipher text is written that is different from random noise. The hidden message is reconstructed by stacking a particular variety of the transparencies and viewing them. The system can be used by anyone without any knowledge of cryptography and without performing any cryptographic computations. Naor and Shamir have developed the Visual Secret Sharing Scheme (VSSS) to implement this model. In k out of n VSSS (which is also called (k, n) scheme), a binary image (picture or text) is transformed into n sheets of transparencies of random images. The original image becomes visible when any k sheets of the n transparencies are put together, but any combination of less than k sheets cannot reveal the original binary image. In the scheme, one pixel of the original image is reproduced by m sub pixels on the sheets. The pixel is considered “on” (transparent) if the number of transparent sub pixels is more than a constant threshold, and “off” if the transparent sub pixels is less than a constant lower threshold, when the sheets are stacked together. The contrast α is the difference between the on and off threshold number of transparent pixels. Ateniese et al. has extended the (k, n) VSSS to general access structures where ever will specify all qualified and out subsets of n participants. Droste thought about the matter of sharing more than one secret image among a set of participants and proposed a method to reconstruct different images with different Combination of sheets.
CONCLUSION
In this paper, we've explored extended visual cryptography while not enlargement. We've shown that using an intelligent pre – processing of halftone pictures supported the characteristics of the first secret image, we tend to square measureable to manufacture smart quality images within the shares and therefore the recovered image. Note that alternative applications may also enjoy the pre-processing approach, like multiple image visual cryptography, that hides multiple pictures in shares.