فصلنامه پدافند غیرعامل
سال دهم شماره 3 (پیاپی 39، پاییز 1398)

The use of social networks to communicate and share information has grown dramatically in recent years. These networks are nowadays used in most areas such as education, business, health and entertainment. The large amount of valuable information on social networks has made them the main target of malicious users, such as spammers and fraudsters, for carrying out abusive and illegal activities. The abnormal and unexpected behavior of these users is identified using anomaly detection methods. Detection of anomalies is important in preventing fraud, dissemination of counterfeit information and configuration of attacks in these networks.  Anomalies are static or dynamic, with or without attributes. In this paper, various methods developed for anomaly detection in social networks have been investigated and categorized and an overview provided on anomaly detection, its applications, existing challenges and key areas for future research.

Protection of civil structures such as towers, bridges, dams, refineries and other large structures against natural and unnatural disasters is one of the topics which should be addressed in the field of passive defense. One of the most important issues which should be regarded for massive structures is monitoring the status of their strength after the construction process. Cracks and fractures caused by subsidence, structural age, humidity, cold and warm air, corrosion, decay, as well as various disasters, are the problems that may occur after construction and can affect structure safety over time. Hence, many of structures in the world, besides being carefully monitored when constructed, are controlled by different systems after construction. One of the most popular types of these systems is distributed optical fiber sensors system. In this article, we first introduce and then compare different types of these sensors in the field of structural defense. After explaining the advantages and disadvantages of each of these distributed sensors and introducing their samples in different structures of the world, we will see that Fiber Bragg Grating sensor is more widely used than any other optical fiber distributed sensor, for monitoring the strength of civil structures.The main reason for the tendency to use Fiber Bragg Grating sensors is cost-effectiveness as they havehigh spatial resolutionand are easy to construct and install.

Regarding the limitations of wired networks, such as geographical constraints, positioning limitations, high cost of building the necessary infrastructure, and construction lag of infrastructures etc, wireless networks have received considerable attention. In the meantime, adhoc mobile networks have received special attention due to the features such as lack of central management and infrastructure, as well as high mobility. A mobile network is a network independent of router nodes connected to each other by wireless links. In this network, routers move randomly and independently organize themselves; therefore, the wireless network topology is changing frequently and unpredictably, which has become one of the challenges of using these networks. If the routing protocol is not selected according to the application’s circumstances, it will cause many problems. In this paper, we explore mobile adhoc networks and then we will propose an optimal routing protocol for mobile military communications. This proposal has been presented with regard to the characteristics of a military connection. The simulation results demonetrate optimal performance of this protocol compared to other protocols.

Each city’s environment and geographic location express the kind of human relationship amongst the citizens. The geographic location of the city which accomodates its infrastructure could be an impairment by itself. Therefore, the spatial distribution of elements, their combination, and the main functions of the city, which form the city's structure, play an important role in the vulnerability of the city to various calamities, particularly threats. Therefore, based on the necessity, the subject of this research which has a developmental-applied nature is to study the passive defense approach in the socio-physical pathology of Ahwaz city using the VIKOR model. It should be noted that this study incorporates a combination of research approaches namely, analytical and descriptive methods, and field and library researches for data preparation, extraction and analysis. The results obtained by VIKOR show the average value of urban crisis vulnerability of Ahwaz to be (0.30)%, the highest and lowest values being (0.97)% and (0.007)% respectively belonging to the area named as Zone 2 of Ahwaz city. City management and urban development are essential for the safety of the city because different locations in the city have different resistance and strength in case of any crisis.

Over the past decades, cryptography has always been a concern for both scientific and industrial researchers. The rapid growth in the field of information technology, along with the introduction of new concepts such as the Internet of Objects, as well as the growing range of users and a variety of new Internet services (such as social networks, cloud services, etc.), have created many challenges and consequently new security criteria are needed. This has led to the rapid growth of cryptographic science. The main purpose of this article is to introduce new approaches in the field of modern cryptography which either provide some new concepts or take significant steps to improve previous efforts. Accordingly, this paper follows three objectives 1. Emphasizing the need to identify and review new cryptographic issues; 2. Clarifying some of the new cryptographic aspects by studying some of the most important developments in cryptography in recent years; 3. Reviewing briefly some of the latest issues and concepts considering future cryptographic orientations.

The growth of Internet and computer networks has led to the ease of information transfer. This development has also caused some problems due to the fact that in network environments, data may be snooped while transferring from the sender to the receiver. So, it is always necessary to provide information security and in order to achieve this goal, steganography plays an important role. Network steganography is a method that uses network protocols. Many techniques for network steganography have been suggested up to this time so that familiarity with different algorithms, as well as recognizing the advantages and disadvantages of each of them, are required for researchers in this field who wish to introduce a new approach to steganography or to propose a new method of steganalysis. In this paper, it has been attempted to describe the various ideas behind network steganography methods in terms of two different classifications, and the result of the research have been presented. Although it would be ideal to devise a method which satisfies the three steganography evaluation criteria: capacity, undetectability and robustness simultaneously, but bearing in mind the conflict between them, a method can be proposed for each application which excels in the criterion that is most relevant in that application.