Biblio

Internet technology has made surveillance widespread and access to resources at greater ease than ever before. This implied boon has countless advantages. It however makes protecting privacy more challenging for the greater masses, and for the few hacktivists, supplies anonymity. The ever-increasing frequency and scale of cyber-attacks has not only crippled private organizations but has also left Law Enforcement Agencies(LEA's) in a fix: as data depicts a surge in cases relating to cyber-bullying, ransomware attacks; and the force not having adequate manpower to tackle such cases on a more microscopic level. The need is for a tool, an automated assistant which will help the security officers cut down precious time needed in the very first phase of information gathering: reconnaissance. Confronting the surface web along with the deep and dark web is not only a tedious job but which requires documenting the digital footprint of the perpetrator and identifying any Indicators of Compromise(IOC's). TORSION which automates web reconnaissance using the Open Source Intelligence paradigm, extracts the metadata from popular indexed social sites and un-indexed dark web onion sites, provided it has some relating Intel on the target. TORSION's workflow allows account matching from various top indexed sites, generating a dossier on the target, and exporting the collected metadata to a PDF file which can later be referenced.

Cloud computing is a unified management and scheduling model of computing resources. To satisfy multiple resource requirements for various application, edge computing has been proposed. One challenge of edge computing is cross-domain data security sharing problem. Ciphertext policy attribute-based encryption (CP-ABE) is an effective way to ensure data security sharing. However, many existing schemes focus on could computing, and do not consider the features of edge computing. In order to address this issue, we propose a cross-domain data security sharing approach for edge computing based on CP-ABE. Besides data user attributes, we also consider access control from edge nodes to user data. Our scheme first calculates public-secret key peer of each edge node based on its attributes, and then uses it to encrypt secret key of data ciphertext to ensure data security. In addition, our scheme can add non-user access control attributes such as time, location, frequency according to the different demands. In this paper we take time as example. Finally, the simulation experiments and analysis exhibit the feasibility and effectiveness of our approach.

The camera constructed by a megahertz range intensity modulation active light source and a kilo-frame rate range fast camera based on compressive sensing (CS) technique for three-dimensional (3D) image acquisition was proposed in this research.

From the perspective of time domain, the propagation characteristics of sound waves in seawater can be seen more intuitively. In order to study the influence and characteristics of seamount on low frequency acoustic propagation, the research of this paper used the Finite Element Method (FEM) based on time domain to set up a full-waveguide low-frequency acoustic propagation simulation model, and discussed the influencing laws about acoustic propagation on seamount. The simulation results show that Seamounts can hinder the propagation of sound waves, weaken the energy of sound waves. The topographic changes of seamounts can cause the coupling and transformation of acoustic signals during the propagation which can stimulate the seabed interface wave.

SummaryIn this study, the propagation and resonance properties of shear-horizontal surface acoustic waves (SH SAWs) on a rotated Y-cut 90°X propagating Ca3TaGa3Si2O14 (CTGS) with a Au- or Al-interdigital transducer (IDT) were investigated theoretically and experimentally. It was found that not only a high-density Au-IDT but also a conventional Al-IDT enables the energy trapping of SH SAW in the vicinity of the surface. For both IDTs, the effective electromechanical coupling factor of about 1.2% and the zero temperature coefficient of frequency can be simultaneously obtained by adjusting the cut angle of CTGS and the electrode film thickness.

Previous research on frequency hopping (FH) signal recognition utilizing deep learning only focuses on single-label signal, but can not deal with overlapped FH signal which has multi-labels. To solve this problem, we propose a new FH signal recognition method based on fully convolutional networks (FCN). Firstly, we perform the short-time Fourier transform (STFT) on the collected FH signal to obtain a two-dimensional time-frequency pattern with time, frequency, and intensity information. Then, the pattern will be put into an improved FCN model, named FH-FCN, to make a pixel-level prediction. Finally, through the statistics of the output pixels, we can get the final classification results. We also design an algorithm that can automatically generate dataset for model training. The experimental results show that, for an overlapped FH signal, which contains up to four different types of signals, our method can recognize them correctly. In addition, the separation of multiple FH signals can be achieved by a slight improvement of our method.

Specific emitter identification (SEI) is a physical-layer-based approach for enhancing wireless communication network security. A well-done SEI method can be widely applied in identifying the individual wireless communication device. In this paper, we propose a novel specific emitter identification method based on variational mode decomposition and histogram of oriented gradient (VMD-HOG). The signal is decomposed into specific temporal modes via VMD and HOG features are obtained from the time-frequency spectrum of temporal modes. The performance of the proposed method is evaluated both in single hop and relaying scenarios and under three channels with the number of emitters varying. Results depict that our proposed method provides great identification performance for both simulated signals and realistic data of Zigbee devices and outperforms the two existing methods in identification accuracy and computational complexity.

The spatial-temporal random variation characteristics of underwater acoustic channel make the difference among the underwater acoustic communication network link channels, which make network performance difficult to predict. In order to better understand the fluctuation and difference of network link channel, we analyze the measured channel data of five links in the Qiandao Lake underwater acoustic communication network experiment. This paper first estimates impulse response, spread function, power delay profile and Doppler power spectrum of the time-varying channel in a short detection time, and compares the time-frequency energy distribution characteristics of each link channel. Then, we statistically analyze the discreteness of the signal to noise ratio, multipath spread and Doppler spread parameter distributions for a total of145 channels over a long observation period. The results show that energy distribution structure and fading fluctuation scale of each link channel in underwater acoustic communication network are obviously different.

A comparative analysis of the classical and approximation methods of spectral analysis of fast-variable processes in technical systems is carried out. It is shown that the approximation methods make it possible to substantially remove the contradiction between the requirements for spectrum smoothing and its frequency resolution. On practical examples of vibroacoustic signals, the effectiveness of approximation methods is shown. The Prony method was used to process the time series. The interactive frequency segmentation method and the direct identification method were used for approximation and frequency characteristics.

The growing internet-based services such as banking and shopping have brought both ease to human's lives and challenges in user identity authentication. Different methods have been investigated for user authentication such as retina, finger print, and face recognition. This study introduces a photoplethysmogram (PPG) based user identity authentication relying on textural features extracted from time-frequency image. The PPG signal is segmented into segments and each segment is transformed into time-frequency domain using continuous wavelet transform (CWT). Then, the textural features are extracted from the time-frequency images using Haralick's method. Finally, a classifier is employed for identity authentication purposes. The proposed system achieved an average accuracy of 99.14% and 99.9% with segment lengths of one and tweeny seconds, respectively, using random forest classifier.

The accurate classification of WiFi-based activity patterns is still an open problem and is critical to detect behavior for non-visualization applications. This paper proposes a novel approach that uses WiFi-based IQ data and short-time Fourier transform (STFT) time-frequency images to automatically and accurately classify human activities. The offsets features, calculated from time-domain values and one-dimensional principal component analysis (1D-PCA) values and two-dimensional principal component analysis (2D-PCA) values, are applied as features to input the classifiers. The machine learning methods such as the bagging, boosting, support vector machine (SVM), random forests (RF) as the classifier to output the performance. The experimental data validate our proposed method with 15000 experimental samples from five categories of WiFi signals (empty, marching on the spot, rope skipping, both arms rotating;singlearm rotating). The results show that the method companying with the RF classifier surpasses the approach with alternative classifiers on classification performance and finally obtains a 62.66% classification rate, 85.06% mean accuracy, and 90.67% mean specificity.

This work describes a concept for extending the Network Time Security (NTS) protocol to enable implementation- independent communication between the NTS key establishment (NTS-KE) server and the connected time server(s). It Alls a specification gap left by RFC 8915 for securing the Network Time Protocol (NTP) and enables the centralized and public deployment of an NTS key management server that can support both secured NTP and secured PTP.

We present a collected overview on how to assess both the accuracy and reliability levels and relate them to the required effort, for different digital methods of synchronizing clocks. The presented process is intended for end users who require time synchronization but are not certain about how to judge at least one of the aspects. It can not only be used on existing technologies but should also be transferable to many future approaches. We further relate this approach to several examples. We discuss in detail the approach of medium-range White Rabbit connections over dedicated fibers, a method that occupies an extreme corner in the evaluation, where the effort is exceedingly high, but also yields excellent accuracy and significant reliability.

Recently, the informatics infrastructure of INRiM Time and Frequency Laboratory has been completely renewed with particular attention to network security and software architecture aspects, with the aims to improve the reliability, robustness and automation of the overall set-up. This upgraded infrastructure has allowed, since January 2020, a fully automated generation and monitoring of the Italian time scale UTC(IT), based on dedicated software developed in-house [1]. We focus in this work on the network and software aspects of our set-up, which enable a robust and reliable automatic time scale generation with continuous monitoring and minimal human intervention.

In modern power grids (PGs), load frequency control (LFC) is effectively employed to preserve the frequency within the allowable ranges. However, LFC dependence on information and communication technologies (ICTs) makes PGs vulnerable to cyber attacks. Manipulation of measured data and control commands known as false data injection attacks (FDIAs) can negatively affect grid frequency performance and destabilize PG. This paper investigates the frequency performance of an isolated PG under coordinated FDIAs. A control scheme based on the combination of a Kalman filter, a chi-square detector, and a linear quadratic Gaussian controller is proposed to detect and mitigate the coordinated FDIAs. The efficiency of the proposed control scheme is evaluated under two types of scaling and exogenous FDIAs. The simulation results demonstrate that the proposed control scheme has significant capabilities to detect and mitigate the designed FDIAs.

Power grids are the most extensive man-made systems that are difficult to control and monitor. With the development of conventional power grids and moving toward smart grids, power systems have undergone vast changes since they use the Internet to transmit information and control commands to different parts of the power system. Due to the use of the Internet as a basic infrastructure for smart grids, attackers can sabotage the communication networks and alter the measurements. Due to the complexity of the smart grids, it is difficult for the network operator to detect such cyber-attacks. The attackers can implement the attack in a manner that conventional Bad Data detection (BDD) systems cannot detect since it may not violate the physical laws of the power system. This paper uses the cross wavelet transform (XWT) to detect stealth false data injections attacks (FDIAs) against state estimation (SE) systems. XWT can capture the coherency between measurements of adjacent buses and represent it in time and frequency space. Then, we train a machine learning classification algorithm to distinguish attacked measurements from normal measurements by applying a feature extraction technique.

This paper presents the application of Compressive Sampling (CS) to the realization of a wideband receiver for distributed spectrum monitoring. The proposed prototype performs the non-uniform sampling CS-based technique, while the signal reconstruction is realized by the Orthogonal Matching Pursuit (OMP) algorithm on a personal computer. A first experimental analysis has been conducted on the prototype by assessing several figures of merit, thus characterizing its performance in the time, frequency and modulation domains. The obtained results demonstrate that the proposed prototype can achieve good performance in all specified domains with Compression Ratios (CRs) up to 10 for a 4-QAM (Quadrature Amplitude Modulation) signal having carrier frequency of 350 MHz and working at a symbol rate of 46 MSym/s.

Traditional DDoS attacks mainly send massive data packets through the attacking machine, consuming the network resources or server resources of the target server, making users unable to use server resources to achieve the purpose of denial of service. This type of attack is called a Flooding-based DDoS (FDDoS) attack. It has the characteristics of large traffic and suddenness. However, Low-rate DDoS (LDDoS) attack is a new type of DDoS attack. LDDoS utilize the TCP congestion control mechanism and sends periodic pulses to attack, which can seriously reduce the TCP flow throughput of the attacked link. It has the characteristics of small traffic and strong concealment. Each of these two DDoS attack methods has its own hard-to-handle characteristics, so that there is currently no particularly effective method to prevent such attacks. This paper uses time-frequency analysis to classify and filter DDoS traffic. The proposed filtering method is designed as a system in the actual environment. Experimental results show that the designed filtering algorithm can resist not only FDDoS attacks, but also LDDoS attacks.

Cryptography is the science or process used for the encryption and decryption of data that helps the users to store important information or share it across networks where it can be read only by the intended user. In this paper, Elliptic Curve Cryptography (ECC) has been proposed because of its small key size, less memory space and high speed. Elliptic curve scalar multiplication is an important part of elliptic curve systems. Here, the scalar multiplication is performed with the help of hybrid Karatsuba multiplier as the area utilization of Karatsuba multiplier is less. An alternative of digital signature algorithm, that is, Elliptic Curve Digital Signature Algorithm (ECDSA) along with the primary operations of elliptic curves have also been discussed in this paper.

The core looseness fault is an important part of transformer fault. The state of the core can be obtained by analyzing the vibration signal. Vibration analysis method has been used in transformer condition monitoring and fault diagnosis for many years, while different methods produce different results. In order to select the correct method in engineering application, five kinds of joint time-frequency analysis methods, such as short-time Fourier transform, Wigner-Ville distribution, S transform, wavelet transform and empirical mode decomposition are compared, and the advantages and disadvantages of these methods for dealing with the vibration signal of transformer core are analyzed in this paper. It indicates that wavelet transform and empirical mode decomposition have more advantages in the diagnosis of core looseness fault. The conclusions have referential significance for the diagnosis of transformer faults in engineering.

In electronic warfare, communication may not counter reconnaissance and jamming without the help of network-station selection of frequency hopping. The competition in the field of electromagnetic spectrum is becoming more and more fierce with the increasingly complex electromagnetic environment of modern battlefield. The research on detection, identification, parameter estimation and network station selection of frequency hopping communication network has aroused the interest of scholars both at home and abroad, which has been summarized in this paper. Firstly, the working mode and characteristics of two kinds of FH communication networking modes synchronous orthogonal network and asynchronous non orthogonal network are introduced. Then, through the analysis of FH signals time hopping, frequency hopping, bandwidth, frequency, direction of arrival, bad time-frequency analysis, clustering analysis and machine learning method, the feature-based method is adopted Parameter selection technology is used to sort FH network stations. Finally, the key and difficult points of current research on FH communication network separation technology and the research status of blind source separation technology are introduced in details in this paper.

With the rapid development of mobile communication technology, the reconnaissance on terminal capability and identity information is not only an important guarantee to maintain the normal order of mobile communication, but also an essential means to ensure the electromagnetic space security. According to the characteristics of 5G mobile communication terminal's transporting capability and identity information, the smart jamming is first used to make the target terminal away from the 5G network, and then the jamming is turned off at once. Next the terminal will return to the 5G network. Through the time-frequency matching detection method, interactive signals of random access process and network registration between the terminal and the base station are quickly captured in this process, and the scheduling information in Physical Downlink Control Channel (PDCCH) and the capability and identity information in Physical Uplink Shared Channel (PUSCH) are demodulated and decoded under non-cooperative conditions. Finally, the experiment is carried out on the actual 5G communication terminal of China Telecom. The capability and identity information of this terminal are extracted successfully in the Stand Alone (SA) mode, which verifies the effectiveness and correctness of the method. This is a significant technical foundation for the subsequent development on the 5G terminal control equipment.

Cyber-attacks detection in modern power systems is undoubtedly indispensable to enhance their resilience and guarantee the continuous production of electricity. As the number of attacks is very small compared to normal events, and attacks are unpredictable, it is not obvious to build a model for attacks. Here, only anomaly-free measurements are utilized to build a reference model for intrusion detection. Specifically, this study presents an unsupervised intrusion detection approach using the k-nearest neighbor algorithm and exponential smoothing monitoring scheme for uncovering attacks in modern power systems. Essentially, the k-nearest neighbor algorithm is implemented to compute the deviation between actual measurements and the faultless (training) data. Then, the exponential smoothing method is used to set up a detection decision-based kNN metric for anomaly detection. The proposed procedure has been tested to detect cyber-attacks in a two-line three-bus power transmission system. The proposed approach has been shown good detection performance.

Elliptic Curve Cryptography (ECC) is a revolution in asymmetric key cryptography which is based on the hardness of discrete logarithms. ECC offers lightweight encryption as it presents equal security for smaller keys, and reduces processing overhead. But asymmetric schemes are vulnerable to several cryptographic attacks such as plaintext attacks, known cipher text attacks etc. Frequency analysis is a type of cipher text attack which is a passive traffic analysis scenario, where an opponent studies the frequency or occurrence of single letter or groups of letters in a cipher text to predict the plain text part. Block cipher modes are not used in asymmetric key encryption because encrypting many blocks with an asymmetric scheme is literally slow and CBC propagates transmission errors. Therefore, in this research we present a new approach to defence against frequency analysis in ECC using K-Means clustering to defence against Frequency Analysis. In this proposed methodology, security of ECC against frequency analysis is achieved by clustering the points of the curve and selecting different cluster for encoding a text each time it is encrypted. This technique destroys the regularities in the cipher text and thereby guards against cipher text attacks.

The identification of spectrum opportunities is a pivotal requirement for efficient spectrum utilization in cognitive radio systems. Spectrum prediction offers a convenient means for revealing such opportunities based on the previously obtained occupancies. As spectrum occupancy states are correlated over time, spectrum prediction is often cast as a predictable time-series process using classical or deep learning-based models. However, this variety of methods exploits time-domain correlation and overlooks the existing correlation over frequency. In this paper, differently from previous works, we investigate a more realistic scenario by exploiting correlation over time and frequency through a 2D-long short-term memory (LSTM) model. Extensive experimental results show a performance improvement over conventional spectrum prediction methods in terms of accuracy and computational complexity. These observations are validated over the real-world spectrum measurements, assuming a frequency range between 832-862 MHz where most of the telecom operators in Turkey have private uplink bands.