Steganography is the discipline of invisible communication by hiding the exchanged secret information (message) in another digital information media (image, video or audio). The existence of the message is kept indiscernible in sense that no one, other than the intended recipient, suspects the existence of the message. The majority of steganography techniques are implemented either in spatial domain or in frequency domain of the digital images while the embedded information can be in the form of plain or cipher message. Medical image steganography is classified as a distinctive case of image steganography in such a way that both the image and the embedded information have special requirements such as achieving utmost clarity reading of the medical images and the embedded messages. There is a contention between the amount of hidden information and the caused detectable distortion of image. The current paper studies the degradation of the medical image when undergoes the steganography process in the frequency domain.

Encryption is a way to secure and verify data that are traded through public communication channels in the presence of intruder party called antagonists. Consequently, the transmitted or stored message can be converted to unreadable form except for intended receivers. The decryption techniques allows intended receiver to reveal the contents of previously encrypted message via secrete keys exchanged exclusively between transmitter and receiver. The encryption and decryption techniques can be applied equally to a message in any form such as text, image, audio or video. The current paper applies and evaluate two different encryption/decryption algorithms to the real-time audio signal. The first one is the well-known RSA encryption and decryption technique, while the second one is a new suggested algorithm based on symmetric cryptography concept. The Matlab Simulink simulator tool is used for acquiring the real-time audio signal and simulating the proposed algorithms. Considering the mathematical nature of the audio signal, the experimental results showed that the RSA method yields an audio signal with low quality while the suggested algorithm yields audio signal with high quality as exact signal as the original one.

This paper introduces an algorithm to address the problem of finding the longest common substring between two documents. This problem is known as the longest common substring (LCS) problem. The proposed algorithm is based on the convolution between the two sequences (named major sequence (X) which is represented as array and the minor one (Y) which is represented as circular linked list. An array of linked lists is established and a new node is created for each match between two substrings. If two or more matches in different locations in string Y share the same location in string X, the corresponding nodes will construct a unique linked-list. Accordingly, by the end of processing, we obtain a group of linked-lists containing nodes arranged in certain manner representing all possible matches between sequences X and Y. The algorithm has been implemented and tested in C# language under Windows platform. The obtained results presented a very good speedups and indicated that impressive improvements had been achieved.