الفهرس 
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Abstract
A plethora of scientific research has been conducted on the process of image encryption and securing information transferred through communication channels. The work of scientists seeking to secure data transfer is constantly being counteracted by hackers and intruders, seeking to illegally steal this information. Different types of methods have been used to secure data; this includes encryption, watermarking, and steganography.In this research study, a new encryption method used in securing images is developed and tested. It is characterized by high security and efficiency. By working on an image’s pixels, a change occurs in the original image resulting in an undefined version. The technique developed in this thesis works by using hyperchaotic maps and substitution boxes (S-boxes) to encode medical images.The characteristics of chaotic maps make them useful in encryption applications. They are characterized by ergodicity, sensitivity to initial conditions, and pseudorandomness. They also possess spaces in their parameters. Low and high-dimensional maps are the two types of classification available for these maps. Low-dimensional maps only have a limited number of variables and parameters, making them simpler in nature and easier to implement. As such, they are predictable, since the chaotic range for the values of their parameters is small. As for high-dimensional maps, they have a larger number of parameters and variables. Thus, their chaotic space has a larger range. This makes them difficult to implement and requires longer times for computation. As such, it is difficult to use them in real world applications.The one-dimension (1D) map, i.e., logistic map, the three-dimensions (3D) map, i.e., 3D Chen chaotic map, and the four- dimensions (4D) map, i.e., 4D hyperchaotic map are the three types of maps used in image encryption, since their effectiveness in this process has been proven. Each type of these maps has its specific use. The first step included using the 3D Chen chaotic map, to randomly shuffle the plain image, to achieve confusion. Four sub-images marked the result of dividing the shuffled image. The 4D hyperchaotic map was then used to develop the security key. This was employed in the generation of four S-boxes, for use on the four sub-images. As an example, the values of the hyperchaotic S-box (1) were used to replace the values of the first sub-image. The same applied, in order, to the other three sub-images, replaced by corresponding hyperchaotic S-boxes. To reach the final encrypted image, the four sub-images were combined and diffused with the help of the BIT-XOR process, using a logistic map. Finally, this image was decrypted to return to the original image.Both encrypted and decrypted images were tested and measured to ensure the efficiency of the proposed encryption scheme. These measurements showed the efficiency and security of this new scheme and its ability to provide the encrypted image with necessary means of security, when it falls under attack by different types of noise.