فصلنامه پدافند الکترونیکی و سایبری
سال سوم شماره 4 (پیاپی 12، زمستان 1394)

Protecting valuable data along the Cyber Security is the one of the strategic issues of cyber defense. The secret sharing scheme is an attractive branch of advanced cryptography that has extremely important role in cyber defense and for the preservation of documents and confidential information against threats such as robbery and unauthorized accesses.In the secret sharing schemes, for increasing security shareholders present a shadow image instead of the genuine share while they are recovering secret images. Thus each shareholder is able to share several images with others by having only one portion of image. In this paper, we define and design a new generating function that by replacing with the Hou Zheng Feng and et.al's generating function, can improved it. Since the new generating function is one-way and hard problem, hence increased the security of improved scheme. Also, with implementation and performing the new scheme again, our revised scheme will be more efficient respect to previous scheme according to the analysis and speed of computations.

Among the variety of GPS signal interference, spoofing is considered as the most dangerous intentional interference. If spoofing signal would have existed in the received signal GPS, wrong information reaches the receiver which causes problems in time and location computation of the receiver. Defense against spoofing includes the spoofing detection and reduction. In this paper, we use the properties of correlation function for spoofing detection . In order to mitigate spoofing, we apply the method of Least Mean Squares (LMS) based on sign-data algorithm. This approach reduces effect of the spoofing interference in the received signal GPS and defends against interference of kind of delay spoofing. The proposed approach have been implemented on real dataset and in the acquisition stage from GPS receiver processing. The results show that the adaptive method based on sign-data algorithm decrease effectiveness of spoofing on average 89 percent. In addition to spoofing reduction, the Position Dilution of Precision (PDOP) parameter improves at all of results. PDOP parameter indicates the spatial position of identified satellites. The PDOP value mitigated from 47 to 2.66 on average.

Botnets are the latest types of internet-scale malware in recent years that has been the greatest threats to the web servers. Bot is an infected computer by a malware that are controlled remotely by one or more human factors without the user’s knowledge. This controller agent called “bot master” and sometimes the infected system is called “victim”. Peer to peer botnet is one type of botnets that use peer to peer protocols and detection of this type of botnet is more difficult than other types. Our suggested approach is a new method to detect such botnets. This approach uses network flow analysis and clustering method in data mining to detect peer to peer botnets. This approach is flow-based and compares the similarity between flows and K-Means clustering algorithm and eventually determines that the new traffic is an attack or not. This approach has good performance in detection of botnets in flash crowd traffic and this characteristic is distinction of the suggested algorithm and similar algorithms. Finally, the suggested approach has been tested with different traffic.

With the growing development of wireless communications systems, the use of systems with high data rates has arrested attention that can be noted to OFDM systems among these systems. The important features of this system are efficient usage of bandwidth and resistance to errors caused by the multipath propagation environment. OFDM systems have a high sensitivity to frequency offset. Due to the importance of signal eavesdropping in the cyber defence, in order to compensate frequency offset, it is necessary to use blind frequency estimation methods based on the inherent structure of the system and without the use of pilot symbols. Accordingly, in this paper, a blind frequency offset estimation algorithm based on cyclic prefix (CP) by using adaptive algorithms is presented that is closed to the optimum frequency offset during a step by step algorithm. In the proposed method, the Normalized Least Mean Square (NLMS) and Recursive least squares (RLS) adaptive algorithms are used to provide a method for estimating the frequency offset. The main feature of the new presented method is the ability to estimating the frequency offset in the presence of the time offset and in multipath channel with frequency-selective fading. According to the simulations results that are performed in the frequency-selective fading channel, MSE criterion in the NLMS proposed method about 3 dB and in the RLS proposed method approximately 7 dB has improved compared to other methods.

Tradeoffs between security and performance are the most important issue in wireless networks. An authentication protocol is a type of cryptographic protocol with the purpose of authenticating entities. Latest standards for re-authentication protocols have published by Internet Engineering Task Force (IETF). In this research, after reviewing some protocols in this scope, a security protocol is proposed. The proposed protocol is based on IETF standards. Fundament of RFC 6696 is exploited to develop the proposed protocol. It offers serious advantages over the existing IEEE 802.1X standard protocols, including: symmetric cryptosystem, challenge–response and hash chaining.