On the Road to Holistic Decision Making in Adaptive Security

Security is a critical concern in today's software systems. Besides the interconnectivity and dynamic nature of network systems, the increasing complexity in modern software systems amplifies the complexity of IT security. This fact leaves attackers one step ahead in exploiting vulnerabilities and introducing new cyberattacks. The demand for new methodologies in addressing cybersecurity is emphasized by both private and national corporations. A practical solution to dynamically manage the high complexity of IT security is adaptive security, which facilitates analysis of the system's behaviour and hence the prevention of malicious attacks in complex systems. Systems that feature adaptive security detect and mitigate security threats at runtime with little or no administrator involvement. In these systems, decisions at runtime are balanced according to quality and performance goals. This article describes the necessity of holistic decision making in such systems and paves the road to future research

Numerical Modeling of the Interactions Between Nonlinear Waves and Arbitrarily Flexible Vegetation

Coastal wetlands are among the natural features with the capability to dissipate wave energy and reduce storm damage. Inadequate representation of wave and vegetation characteristics in numerical models may reduce their capability in predicting wave processes over wetlands. Previous numerical wave models have typically applied simplifications on vegetation behavior. For instance, vegetation stems were usually assumed to be rigid or semi-flexible and thus extreme stem deflections could not be captured. In this study, a time-domain nonlinear numerical model based on extended Boussinesq formulation is developed and coupled with a numerical model for vegetation blade dynamics that allows for arbitrary flexibility. Comparison with analytical and laboratory experiments show that the coupled model can adequately predict flow as well as vegetation blade dynamics without the need for any parameter tuning. The model is then used to obtain wave-induced forces on a stem and vegetation blade orientation. Model results indicate that the variation of the vegetative drag coefficient with wave frequency is non-monotonic

Towards an Uncertainty-Aware Adaptive Decision Engine for Self-Protecting Software: an POMDP-based Approach

The threats posed by evolving cyberattacks have led to increased research related to software systems that can self-protect. One topic in this domain is Moving Target Defense (MTD), which changes software characteristics in the protected system to make it harder for attackers to exploit vulnerabilities. However, MTD implementation and deployment are often impacted by run-time uncertainties, and existing MTD decision-making solutions have neglected uncertainty in model parameters and lack self-adaptation. This paper aims to address this gap by proposing an approach for an uncertainty-aware and self-adaptive MTD decision engine based on Partially Observable Markov Decision Process and Bayesian Learning techniques. The proposed approach considers uncertainty in both state and model parameters; thus, it has the potential to better capture environmental variability and improve defense strategies. A preliminary study is presented to highlight the potential effectiveness and challenges of the proposed approach

A Numerical Study on Surface Wave Evolution Over Viscoelastic Mud

A numerical modeling approach is applied to investigate the combined effect of wave-current-mud on the evolution of nonlinear waves. A frequency-domain phase-resolving wave-current model that solves nonlinear wave-wave interactions is used to solve wave evolution. A comparison between the results of numerical wave model and the laboratory experiments confirms the accuracy of the numerical model. The model is then applied to consider the effect of mud properties on nonlinear surface wave evolution. It is shown that resonance effect in viscoelastic mud creates a complex frequency-dependent dissipation pattern. In fact, due to the resonance effect, higher surface wave frequencies can experience higher damping rates over viscoelastic mud compared to viscous mud in both permanent form solution and random wave scenarios. Thus, neglecting mud elasticity can result in inaccuracies in estimating total wave energy and wave shape

Nonlinear Wave Evolution in Interaction With Currents and Viscoleastic Muds

A numerical model is extended to investigate the nonlinear dynamics of surface wave propagation over mud in the presence of currents. A phase-resolving frequency-domain model for wave-current interaction is improved to account for wave modulations due to viscoelastic mud of arbitrary thickness. The model compares well with published laboratory data and performs slightly better than the model with viscous mud-induced wave damping mechanism. Monochromatic and random wave simulations are conducted to examine the combined effect of currents, mud-induced wave dissipation and modulation, and nonlinear wave-wave interactions on surface wave spectra. Results indicate that current effects on wave damping over viscoelastic mud is not as straightforward as that over viscous mud. For example, while opposing currents consistently increase damping of random waves over viscous mud, they can decrease damping over viscoelastic mud due to high variations in frequency-dependent damping stemming from mud’s elasticity. It is shown that a model that assumes the mud layer to be thin for simplification can overestimate wave damping over thick mud layers

Optimizing Nature-Based Features for Wave Dissipation and Land-Water Connectivity

Living shorelines integrate structural and natural features to stabilize the shoreline, through reduction of erosion from the wave climate, while keeping the connectivity between land and aquatic ecosystems. This study includes field study for two different types of living shoreline systems to quantify and compare their wave dissipation services and provide physics-based guidance for the design of living shoreline systems that are efficient in wave dissipation yet maximize land-water connectivity