In this paper, a novel algorithm for image encryption based on SHA-512 is proposed. The main idea of the algorithm is to use one half of image data for encryption of the other half of the image reciprocally. Distinct characteristics of the algorithm are high security, high sensitivity and high speed that can be applied for encryption of gray-level and color images. The algorithm consists of two main sections: The first does preprocessing operation to shuffle one half of image. The second uses hash function to generate a random number mask. The mask is then XORed with the other part of the image which is going to be encrypted. The aim of this work is to increase the image entropy. Both security and performance aspects of the proposed algorithm are analyzed and satisfactory results are achieved in various rounds.

With the advent of new technologies and various services provided in the context of computer networks, a large volume of data is being generated. The main challenge in this area is providing network protection services against various threats and vulnerabilities. So far, many techniques have been proposed to deal with these threats. All of these techniques pursue the same goal, preventing attackers from reaching their objectives. A solution based on early warning system(s) (EWSs) is what exactly security teams need to manage the threats properly. EWS, as a complement to Intrusion Detection System, is a proactive approach against security threats. This is carried out through the early detection of potential behavior of a system, evaluating the scope of malicious behavior, and finally, using suitable response against any kind of detectable security event. This paper presents a comprehensive review on EWSs including definitions, applications, architectures, alert correlation aspects, and other technical requirements. Furthermore, previous studies and existing EWSs have been described and analyzed here. A classification of EWSs has been presented: commercial systems and systems under research and development. Finally, from the studies about EWSs, we conclude some challenges and research issues are still remain open. Copyright © 2016 John Wiley & Sons, Ltd.