Beschreibung
Master's Thesis from the year 2009 in the subject Computer Science - IT-Security, grade: 19.61 / 20, language: English, abstract: Cryptography is a technology intended to provide protection to digital data being transmitted over communications systems. It provides mathematical methods for converting data into an unreadable form. In the other hand, Steganography is a technique by which the secret digital data is sent from one side to another by embedding it into an innocent-looking digital cover, so the existence of hidden data is concealed. Cryptography and Steganography can work together where combining them provides two-layers protection; The former encrypts the secret message, so it becomes unreadable; the latter hides the encrypted message into an innocent-looking digital cover, so it can not be seen. In this thesis, we briefly review the principles of cryptography and its algorithms, while we achieve a detailed study in the field of JPEG-based steganography since JPEG format is the most frequently used through the internet. In Chapter 2, we present the structure of JPEG format and the related subjects; DCT transformation, and entropy coding. In Chapter 3, we present some well known DCT-based methods: F3, F5, and Mod4 and show their properties and features. In Chapter 4, we present a comparison between DCT-based steganographic methods F3, F5, and Mod4. The study was implemented via Matlab, where the required codes were written accordingly. In this study, three steganographic requirements are considered; capacity, image quality, and statistical properties. The study shows that F3 has a large capacity, but it can be detected easily. Also, the study shows that Mod4 has a small capacity, but it can NOT be detected easily. The comparison shows that the traditional F5_ME takes a middle position between the considered algorithms. In order to visually compare the considered algorithms, a Magic Triangle Model is presented In Chapter 5, we discuss the shrinkage occurring during the embedding process of F5; we present all the effects of shrinkage caused by F5. In order to reduce the shrinkage rate, we proposed a new method called F5_MOS. The new method controls the shrinkage by building a Map Of Shrinkage. A comparison study is implemented between the proposed method F5_MOS, and the traditional F5_ME considering the main steganographic requirements. The comparison shows how F5_MOS provides more capacity and how it makes the hidden message more undetectable. NOTE: The thesis contains all the tables of numerical results and all the used images.
Autorenporträt
Email : wasim.kchm@gmail.com
Herstellerkennzeichnung:
BoD - Books on Demand
In de Tarpen 42
22848 Norderstedt
DE
E-Mail: info@bod.de
