الفهرس 
DIFFUSION BASED IMAGE ENCRYPTIONOnly 14 pages are availabe for public view
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Abstract
Transmission of images in different communication systems is a very
important topic that attracted the attention of researchers in the last few decades.The endeavor towards an optimum encryption scheme and an optimum modulation method for this purpose is still under consideration. Orthogonal frequency division multiplexing (OFDM) is an attractive multicarrier transmissiontechnique for wideband communications, because it effectively transforms the frequency selective fading channel into a flat fading channel. Hence, OFDM provides greater immunity to multipath fading and impulsive noise, and eliminates the need for complicated equalizers. However, OFDM communication systems suffer from fading effects, high sensitivity to carrier frequency offsets and phase noise. In this thesis, we present a study for two different families of encryption schemes; permutation based schemes and diffusion based schemes. The objective of this study is to select the more suitable scheme for encrypted image br>transmission over communication systems. Encryption and decryption quality metrics are used in the presented comparison. Two modifications are presented in this thesis in the permutation and diffusion algorithms to enhance their properties. Different versions of OFDM in the presence of Carrier Frequency OffsetCFO) are studied in the thesis for the possible choice of the most appropriate
version for encrypted image transmission. OFDM signal has large amplitude fluctuations and so a high PAPR. This high PAPR requires system components with a wide linear range to accommodate for the signal variations. Otherwise, nonlinear distortion, which results in a loss of subcarrier orthogonality and hence a degradation in the system performance occurs. The effects of equalization,CFO compensation and PAPR reduction methods on encrypted image transmission are also studied in the thesis. Finally we discuss sampling clock offset.