Security Margin Research Articles

Investigation of an Effective Strategy for Computing Small-Signal Security Margins

As the operational conditions of power systems change, the operating point (i.e., the equilibrium point) may approach the small-signal security boundary. Given the current operating condition as well as the load and generation variations, it is meaningful to compute the small-signal security margin (SSSM). In this paper, an effective method that consists of three stages to compute the SSSM is proposed and examined. In the first stage, which is an estimation stage, the critical mode crossing the damping ratio line is estimated. The SSSM is then computed by a test function or by a direct method in the second stage, which is a correction stage. The computational results are then verified in the third stage, which is a verification stage. Numerical results on a 10-machine and a 160-machine system (with the state variables being 1600) show that the proposed three-stage method is efficient and promising.

Partial Redesign of an Accelerator Driven System Target for Optimizing the Heat Removal and Minimizing the Pressure Drops

Accelerator Driven Systems (ADS) seem to be a good solution for safe nuclear waste transmutation. One of the most important challenges for this kind of machine is the target design, particularly for what concerning the target cooling system. In order to optimize this component a CFD-based approach has been chosen. After the definition of a reference design (Be target cooled by He), some parameters have been varied in order to optimize the thermal-fluid-dynamic features. The final optimized target design has an increased security margin for what regarding Be melting and reduces the maximum coolant velocity (and consequently even more the pressure drops).

Reactive side-channel countermeasures: Applicability and quantitative security evaluation

The security of cryptographic implementations running on embedded systems is threatened by side-channel attacks. Such attacks retrieve a secret key from a computing device observing the information leaking on unintended channels such as the energy consumed during a computation. The vast majority of the countermeasures proposed against such attacks aims at preventing the attacker from exploiting fruitfully the information leaking on the side-channel either altering it or hiding it within a higher noise envelope. Whilst all these countermeasures provide a quantitative security margin against an attacker, they do not provide an indication of having been successfully overcome, thus forsaking the possibility of taking a reactive action upon an eventual security breach. In an effort to propose a reactive countermeasure, we describe our proposal suggesting the introduction of redundant computations employing fixed fake keys (a.k.a. chaffs) to pollute the leaked information with plausible albeit deceitful one. We provide an in depth analysis of the proposed approach, highlighting the constraints to its effective applicability, and the boundary conditions which allow its employment for the securization of a system. We detail the attacker model considered, and the reactive security margin provided by the proposed scheme, highlighting the extent of the realizability of a reactive countermeasure, given the nature of the side-channel information. To provide experimental backing to our analysis, effectiveness and efficiency results on the Advanced Encryption Standard (AES) cipher implementation as well as lightweight block ciphers implementations running on an ARM Cortex-M4 processor are shown.

Adaptive Control of Microgrid Security

The low inertia of inverter-based distributed energy resources (IBDERs) can threaten the dynamic security of microgrids (μGs) and make μGs more susceptible to incipient fault transients. This letter proposes a control approach to improve the transient response of IBDER and maintain a reasonable dynamic security margin for μGs. The IBDER is controlled to mimic the inertial response and voltage support characteristic of synchronous generators subjected to severe disturbances. The proposed method adapts to various μG conditions and maintains the coherency of IBDER with synchronous generator-based distributed energy resources.

Mathematical modeling of electric vehicles contributions in voltage security of smart distribution networks

This paper evaluates the voltage security of the distribution networks in the presence of electric vehicles in the optimization framework. Accordingly, the main objective functions of this optimization problem include maximization of voltage security margin and minimization of operational cost. Also, it is supposed that the electric vehicles are equipped with bidirectional chargers to control active and reactive power in smart distribution networks, simultaneously. The objective functions are subject to the constraints of power flow equations, system operating limits and electric vehicle constraints. The proposed model is implemented on the 33-bus distribution network to evaluate the performance of the proposed optimization scheme for the management of the smart distribution networks in the presence of electric vehicles. The results show that the operational cost and network voltage security margin are reduced in the case of the higher electric vehicle penetration rate when electric vehicles are used for charging active power and reactive power control capability, with respect to the case that does not include electric vehicles.

Trade-off of security and performance of lightweight block ciphers in Industrial Wireless Sensor Networks

Lightweight block ciphers play an indispensable role for the security in the context of pervasive computing. However, the performance of resource-constrained devices can be affected dynamically by the selection of suitable cryptalgorithms, especially for the devices in the resource-constrained devices and/or wireless networks. Thus, in this paper, we study the trade-off between security and performance of several recent top performing lightweight block ciphers for the demand of resource-constrained Industrial Wireless Sensor Networks. Then, the software performance evaluation about these ciphers has been carried out in terms of memory occupation, cycles per byte, throughput, and a relative good comprehensive metric. Moreover, the results of avalanche effect, which shows the possibility to resist possible types of different attacks, are presented subsequently. Our results show that SPECK is the software-oriented lightweight cipher which achieves the best performance in various aspects, and it enjoys a healthy security margin at the same time. Furthermore, PRESENT, which is usually used as a benchmark for newer hardware-oriented lightweight ciphers, shows that the software performance combined with avalanche effect is inadequate when it is implemented. In the real application, there is a need to better understand the resources of dedicated platforms and security requirement, as well as the emphasis and focus. Therefore, this case study can serve as a good reference for the better selection of trade-off between performance and security in constrained environments.

Post-cesarean scar endometriosis.

Objective:Endometriosis is seen in women during their reproductive period, where stromal tissue and functional endometrial glands of the uterus are observed outside the uterine cavity. In this study, we aimed to identify the clinical characteristics of our patients who underwent surgery with scar endometriosis and to discuss the surgical results in light of the literature.Materials and Methods:A total of 24 patients who underwent surgery and diagnosed as having endometriosis as the result of a pathologic examination were retrospectively evaluated.Results:The mean age of the patients was 31 years. Thirteen presented to general surgery and 11 presented to gynecology outpatient clinics. The pain was cyclical in 19 patients. There was history of cesarean section in 9 patients, twice in 12, and 3 times in three patients. The mean diameter was 39.1 mm on ultrasound, and 37.5 mm on magnetic resonance imaging. Endometriosis was on the left side of the incisions in 13, whereas it was on the right in 11. The mean weight of the lesions was 61.6 grams.Conclusion:The occurrence of endometriosis is supported by the iatrogenic implantation theory. In the event of a mass in the abdominal wall, previous obstetric and gynecologic operations and a history of a painful mass during menstruation periods must be questioned. In the treatment of scar endometriosis, excision is required by obtaining secure margins. If diagnosis can be established preoperatively, unnecessary surgeries can prevented.

Distribution network reconfiguration comprehensively considering N −1 security and network loss

Efficiency pursuit of the distribution system operation should be on the premise of security. This study proposes the network reconfiguration (NR) approach comprehensively considering N -1 security and network loss. A new approach called distribution system security region (DSSR) is first applied in NR problem. The DSSR is the feasible operation space of a system within N -1 security criterion and can quantify the N -1 security margin. Then, the NR is formulated by using the minimum network loss as objective function and the N -1 security margin, which is provided by the DSSR, as constraints. Moreover, the security margin constraints can be customised for each feeder individually, yielding proper compromises between security-related and efficient concerns. Different NR results for multiple security and efficiency requirements are presented on an extended IEEE-RBTS test system. Compared with the traditional minimum-loss NR, the proposed approach reduces the network loss as much as possible with desired security margin, well balancing the security and efficiency of NR.

Optimal Borehole Energy Storage Charging Strategy in a Low Carbon Space Heat System

Domestic heating is the major demand of energy systems, which can bring significant uncertainties to system operation and shrink the security margin. From this aspect, the borehole system, as an interseasonal heating storage, can effectively utilize renewable energy to provide heating to ease the adverse impact from domestic heating. This paper proposes an optimal charging strategy for borehole thermal storage by harvesting energy from photovoltaic (PV) generation in a low-carbon space heating system. The system optimizes the heat injection generated by air source heat pump in the charging seasons to charge the borehole, which provides high inlet temperature for ground source heat pump to meet space heating demand in discharging seasons. The borehole is modeled by partial differential equations, solved by the finite-element method at both 2D and 3D for volume simulation. The pattern search optimization is used to resolve the model. The case study illustrates that with the optimal charging strategies, less heat flux injection can help the borehole to reach a higher temperature so that the heating system is more efficient compared with boilers. This paper can benefit communities with seasonable borehole storage to provide clean but low-cost heating and also maximize PV penetration.

Multi-objective bi-level planning of active distribution networks considering network transfer capability and dispersed energy storage systems

This study proposes an expansion planning method to maximize the benefits of feeder interconnection and distributed generation (DG) allocation in active distribution networks (ADNs). The proposed method considers four active management schemes (i.e., on-load tap-changer voltage control, DG curtailment, DG power factor control, and demand side management) and uncertainties (i.e., contingencies, load fluctuation, and DG output power). The network transfer capability of the ADN after an N-1 contingency and the optimization of dispersed energy storage systems for peak shaving and renewable energy compensation are also integrated in this study. The reinforcements deemed in this method are wiring reformation, new wiring, substation expansion, and DG installation. The objectives of the model in this paper are cost and security. The system security is evaluated by a defined security margin index under restoration after a contingency. Numerical results are presented for a modified 104-bus distribution network to verify the proposed method.

PMU-Based Estimation of Synchronous Machines’ Unknown Inputs Using a Nonlinear Extended Recursive Three-Step Smoother

Knowledge of the synchronous machines’ control input signals and internal states can provide valuable insight to system operators for assessing security margins and the stability of the power system. For example, during disturbances in a stressed power system, it can be of great value to monitor the performance of the machine’s control system, e.g., the response of the field voltage, mechanical power, and the field current. As there are often no real-time power plant measurements available to power system operators, internal states, and unknown inputs of generator units would need to be estimated from synchrophasor measurements. This paper proposes a new estimation algorithm, the nonlinear extended recursive three-step smoother (NERTSS), to simultaneously estimate the states and the unknown inputs of the synchronous machine using data from phasor measurement units. These quantities can then be used to monitor the performance of the machine’s controls. The case studies presented in the paper compare the estimation performance of the NERTSS with the extended Kalman filter with unknown inputs (EKF-UI) when noisy synchrophasor measurements are used. The simulation results show that the proposed estimation method compares favorably with respect to the EKF-UI in terms of the achieved estimation accuracy.

Ethoxysulfuron no controle de plantas daninhas na cultura do feijoeiro comum

É necessário identificar novos herbicidas com amplo espectro de controle de plantas infestantes para a cultura do feijão e, que possuam margem de segurança adequada para a cultura. Os objetivos deste trabalho foram, avaliar o potencial uso do herbicida ethoxysulfuron para o controle de plantas infestantes em meio a cultura do feijão, assim como a tolerância da cultivar de feijão IAC Imperador a este herbicida. Um experimento foi conduzido a campo em delineamento de blocos ao acaso com parcelas subdivididas. Nas parcelas principais foram alocadas as doses de ethoxysulfuron (0; 10,4; 20,8; 41,6; 62,5 e 83,3 g ha-1) e nas sub parcelas três cultivares de soja (AMS Tibagi, Dow 5D634 e Nidera 5909) + as plantas infestantes (Bidens spp., Ipomoea spp.). Adicionalmente foi incluído um tratamento extra sem infestantes e sem aplicação do herbicida. Ethoxysulfuron controlou as plantas de Ipomoea spp. e soja, mas não as de Bidens spp. Constatou-se tolerância diferencial entre as cultivares de soja avaliadas, em que a cultivar AMS Tibagi indica ser ligeiramente mais tolerante que as demais cultivares. Doses de até 20,8 g ha-1 são suficientes para controlar satisfatoriamente plantas de Ipomoea spp. e soja, no entanto, não as de Bidens spp. O herbicida proporcionou incremento no rendimento de grãos de feijão, todavia, não foi suficiente para alcançar o rendimento da testemunha extra. A cultivar de feijão IAC Imperador demostrou tolerância moderada ao ethoxysulfuron, além disso, as plantas tendem a se recuperar rapidamente da injúria do herbicida.

Short Sales Mechanism, Litigation Risk and Audit Fees

This paper examines how the short sales mechanism affects firms' audit fees through the changes in litigation risk, based on the natural experiment of securities margin trading in China. It comes to the conclusions that the introduction of short sales mechanism reinforces the pressure of the fall in stock prices and strengthens the incentive of investors to search bad news of companies, leading to the increase in audit litigation risk of companies and higher audit fees required by accounting firms. Further analysis suggests that the short sales mechanism plays a more obvious role in the increase in audit fees of state-owned enterprises, owing to poor information disclosure environment in state-owned enterprises; due to stronger compensation capacities of Big Four, the short sales mechanism significantly results in the rise in audit fees of Big Four; as for enterprises located in areas with poorer legal environment, because the management has the motivations to hide bad news, their audit fees significantly increase because of the existence of the short sales mechanism.

卖空机制、股价信息含量与暴跌风险——基于融资融券交易的经验证据

This paper makes use of the natural experimental opportunity that China has gradually introduced margin trading in stock market, and investigates the effect of short selling on stock pricing efficiency in reflecting negative information by using a difference-in-difference research design. Using the data from 2007 to 2012, it concludes that compared with non-target stocks, after the stocks become the underlying assets of securities margin trading, their stock prices react more timely to downward market volatility, thus reducing the asymmetric stock price reaction between positive and negative market information, which means that prices for underlying stocks of securities margin trading embed bad news of corporate values more timely and fully. At the same time, compared with non-target stocks, after the stocks become the underlying assets of securities margin trading, the probability of stock price crashes is significantly reduced. These results suggest that short selling improves the stock pricing efficiency in reflecting negative information after China introduces the securities margin trading.

Restoring desired voltage security margin based on demand response using load-to-source impedance ratio index and PSO

Demand Response (DR) is an active role of end-users in responding to signals coming from the market or to emergency signals coming from system operators, asking for a load reduction to help facing criticalities and reduce blackout risks. Load reduction is one of the typical DR participation methods for large and small consumers which is generally considered as a final defence strategy against system instability when voltage collapse is anticipated and may potentially result in blackout. In this paper, an algorithm concerning load reduction based DR is proposed. Indeed, a two-state algorithm based on finding optimal load reduction pattern and estimating threshold voltage of initiating DR is presented to prevent power system from voltage collapse. In this regard, load-to-source impedance ratio (ZL/XTh) is adopted as an index for evaluating voltage security margin (VSM) and is utilized in an optimization algorithm aimed at obtaining minimum load to be cut down. The proposed approach has been implemented in IEEE 39-bus network demonstrating its effectiveness and applicability.

Towards Accurate Statistical Analysis of Security Margins: New Searching Strategies for Differential Attacks

In today's world of the internet, billions of computer systems are connected to one another in a global network. The internet provides an unsecured channel in which hundreds of terabytes of data is being transmitted daily. Computer and software systems rely on encryption algorithms such as block ciphers to ensure that sensitive data remains confidential and secure. However, adversaries can leverage the statistical behavior of underlying ciphers to recover encryption keys. Accurate evaluation of the security margins of these encryption algorithms remains to be a big challenge. In this paper, we tackle this issue by introducing several searching strategies based on differential cryptanalysis. By clustering differential paths, the searching algorithm derives more accurate distinguishers as compared to examining individual paths, which in turn provides a more accurate estimation of cipher security margins. We verify the effectiveness of this technique on ciphers with the generalized Feistel and SPN structures, whereby the best distinguishers for each of the investigated ciphers were obtained by discovering clusters with thousands of paths. With the KATAN block cipher family as a test case, we also show how to apply the searching algorithm alongside other cryptanalysis techniques such as the boomerang attack and related-key model to obtain the best cryptanalytic results. This also depicts the flexibility of the proposed searching scheme, which can be tailored to improve upon other differential attack variants. In short, the proposed searching strategy realizes an automated security evaluation tool with higher accuracy compared to previous techniques. In addition, it is applicable to a wide range of encryption schemes which makes it a flexible tool for both academic research and industrial purposes.

A Security Analysis of Deoxys and its Internal Tweakable Block Ciphers

In this article, we provide the first independent security analysis of Deoxys, a third-round authenticated encryption candidate of the CAESAR competition, and its internal tweakable block ciphers Deoxys-BC-256 and Deoxys-BC-384. We show that the related-tweakey differential bounds provided by the designers can be greatly improved thanks to a Mixed Integer Linear Programming (MILP) based search tool. In particular, we develop a new method to incorporate linear incompatibility in the MILP model. We use this tool to generate valid differential paths for reduced-round versions of Deoxys-BC-256 and Deoxys-BC-384, later combining them into broader boomerang or rectangle attacks. Here, we also develop a new MILP model which optimises the two paths by taking into account the effect of the ladder switch technique. Interestingly, with the tweak in Deoxys-BC providing extra input as opposed to a classical block cipher, we can even consider beyond full-codebook attacks. As these primitives are based on the TWEAKEY framework, we further study how the security of the cipher is impacted when playing with the tweak/key sizes. All in all, we are able to attack 10 rounds of Deoxys-BC-256 (out of 14) and 13 rounds of Deoxys-BC-384 (out of 16). The extra rounds specified in Deoxys-BC to balance the tweak input (when compared to AES) seem to provide about the same security margin as AES-128. Finally we analyse why the authenticated encryption modes of Deoxys mostly prevent our attacks on Deoxys-BC to apply to the authenticated encryption primitive.

Asymmetric Biclique cryptanalysis of lightweight block ciphers MIBS and I-PRESENT

The security evaluation of lightweight block ciphers plays a critical role in determining the security margins for these ciphers. One method for finding the security margin of a block cipher is Biclique cryptanalysis. In this paper, we present a new schematic for a Biclique attack, which combines asymmetric Biclique and early-abort techniques. We then apply the proposed schematic to MIBS-80 and I-PRESENT-128 to evaluate their security margins. The cryptanalysis for MIBS-80 has a computational complexity of $2^{78.62}$ and a data complexity of $2^{64}$. The cryptanalysis for I-PRESENT-128 has a computational complexity of $2^{127.07}$ and a data complexity of $2^{64}$. Compared to existing schemes, the computational complexity of the two schemes presented here is significantly reduced. Because the total complexity of cryptanalysis depends on the computational complexity, the proposed scheme provides significant advantages. Additionally, this study is the first to use an asymmetric Biclique to attack a full-round I-PRESENT-128.

Preventive Security-Constrained Optimal Power Flow Considering UPFC Control Modes

The successful application of the unified power flow controller (UPFC) provides a new control method for the secure and economic operation of power system. In order to make the full use of UPFC and improve the economic efficiency and static security of a power system, a preventive security-constrained power flow optimization method considering UPFC control modes is proposed in this paper. Firstly, an iterative method considering UPFC control modes is deduced for power flow calculation. Taking into account the influence of different UPFC control modes on the distribution of power flow after N-1 contingency, the optimization model is then constructed by setting a minimal system operation cost and a maximum static security margin as the objective. Based on this model, the particle swarm optimization (PSO) algorithm is utilized to optimize power system operating parameters and UPFC control modes simultaneously. Finally, a standard IEEE 30-bus system is utilized to demonstrate that the proposed method fully exploits the potential of static control of UPFC and significantly increases the economic efficiency and static security of the power system.

Model, Characterization, and Analysis of Steady-State Security Region in AC/DC Power System with a Large Amount of Renewable Energy

A conventional steady-state power flow security check only implements point-by-point assessment, which cannot provide a security margin for system operation. The concept of a steady-state security region is proposed to effectively tackle this problem. Considering that the commissioning of the increasing number of HVDC (High Voltage Direct Current) and the fluctuation of renewable energy have significantly affected the operation and control of a conventional AC system, the definition of the steady-state security region of the AC/DC power system is proposed in this paper based on the AC/DC power flow calculation model including LCC/VSC (Line Commutated Converter/Voltage Sourced Converter)-HVDC transmission and various AC/DC constraints, and hence the application of the security region is extended. In order to ensure that the proposed security region can accurately provide global security information of the power system under the fluctuations of renewable energy, this paper presents four methods (i.e., a screening method of effective boundary surfaces, a fitting method of boundary surfaces, a safety judging method, and a calculation method of distances and corrected distance between the steady-state operating point and the effective boundary surfaces) based on the relation analysis between the steady-state security region geometry and constraints. Also, the physical meaning and probability analysis of the corrected distance are presented. Finally, a case study is demonstrated to test the feasibility of the proposed methods.