الفهرس 
Introduction
Password attacksOnly 14 pages are availabe for public view
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Abstract
The growth of the Internet and the paradigm shift to the World Wide Web (WWW) technology has enabled personal computers to be used as a general communication tool. As in the case of other forms of communication there is a desire for security and privacy. This desire can be achieved by different methods, such as Encryption and Information Hiding. Although Encryption techniques are efficient and easy to apply, the rules imposed by many governments restrict the use of them. This motivates the researchers to find new techniques for securing exchanging information. In this thesis, Information Hiding techniques are studied in details. It is an ancient art of embedding private messages in seemingly innocuous messages in such a way that prevents the detection of the secret messages by a third parity. They have three main properties, invisibility, capacity, and robustness. A reasonable compromise is always a necessity for each application. Information hiding techniques can be used in a variety of fields such as, digital watermarking, content labeling, hidden annotations, authentication, integrity verification as well as secure communication. A new technique named ?Improving Visual and Statistical Properties (IVSP) Model? is proposed. This model aims to improve visual properties of the stegoimage by using two components, Minimum Error Replacement (MER) that minimizes the embedding induced error, and Improved Gray Scale Compensation (IGSC) that eliminates the false contours. In addition, the proposed model improves the statistical properties of the stegoimage by restoring the correlation of 1?s and 0?s in JPEG gray scale images. This thesis consists of six chapters organized as follows: In chapter 1, a general Introduction is introduced. In chapter 2, firewall technology and, the concept of Cryptography are reviewed to show to what extent encryption could secure data. In chapter 3, basic concepts of Information Hiding are introduced by reviewing Information Hiding ideas. Also, the properties and requirements for general information hiding techniques along with their performance metrics, which are used to compare Information Hiding algorithms, are presented. Chapter 4, presents the methodologies of some existing techniques of information hiding used for secret communication and digital watermarking over different digital media such as text, images, sounds, and even software programs.