الفهرس 
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Abstract
As the telecommunication technologies grow rapidly, many applications
such as Internet, multimedia applications and military applications need
to enter the era of visual communication, especially visual cryptography.
Transferring images through network (especially Internet) makes them
vulnerable to eavesDROPping or unauthorized users who may tap into the
systems, by reading the image or changing its content. So it is important
to employ the encryption mechanism to protect an image against image
data reading, or data alteration, addition and deletion, especially images
which is related to the national security or classified researches.
However there are many encryption methods which were used for image
protection against data reading. All of them aim to hide all the details of
image by converting it to ciphered image. Using encryption techniques is
more powerful way for this purpose.
This thesis investigates the performance of the application of Data
encryption standard as a popular encryption scheme on two kinds of
images, the Bitmap image which is the best choice for representing subtle
gradations of shades and color such as screen shots or simple painted
images, and the JPEG image which is the best choice for continuous tone
images such as photographs. The method of application of DES on the
image in each case is explained. A mean square error measure between
the original image and the decrypted image was considered to evaluate
the efficiency of encryption. Also the time of encryption in the case of
JPEG and BMP image was measured for a number of selected images
that are different in their size. Finally, a measure for the quality of
encryption was introduced and applied to each case.
The performance results of the application of DES on images saved in
BMP or JPEG format have been shown in graphical forms. Also the
results of measuring the mean square error between the original image
and the decrypted image were documented in tabular and graphical
forms. In addition the results of measuring the encryption tune of images
in each of the two cases are presented in tabular forms for a selected
group of images. Finally the results of measuring the quality of
encryption in each case were presented in histograms and plotted curves.
The software used for implementing DES and its application on the both
JPEG and BMP images and making the comparison study is written in
C++, it was performed on a 400 Mllz Fentium II PC machine with 32
megabytes main memory, running on Windows 98. All programs were
implemented in Microsoft/visual C ++6.0. The Paint Shop Pro version 7
was used to display the encrypted image and decrypted one, and to
extract the difference image.