Simulation-based Paradigm Research Articles

A Case Study on Pathogen Transport, Deposition, Evaporation and Transmission: Linking High-Fidelity Computational Fluid Dynamics Simulations to Probability of Infection

A high-fidelity, low-Mach computational fluid dynamics simulation tool that includes evaporating droplets and variable-density turbulent flow coupling is well-suited to ascertain transmission probability and supports risk mitigation methods development for airborne infectious diseases such as COVID-19. A multi-physics large-eddy simulation-based paradigm is used to explore droplet and aerosol pathogen transport from a synthetic cough emanating from a kneeling humanoid. For an outdoor configuration that mimics the recent open-space social distance strategy of San Francisco, maximum primary droplet deposition distances are shown to approach 8.1 m in a moderate wind configuration with the aerosol plume transported in excess of 15 m. In quiescent conditions, the aerosol plume extends to approximately 4 m before the emanating pulsed jet becomes neutrally buoyant. A dose–response model, which is based on previous SARS coronavirus (SARS-CoV) data, is exercised on the high-fidelity aerosol transport database to establish relative risk at eighteen virtual receptor probe locations.

DABKE: Secure deniable attribute-based key exchange framework

We introduce the first deniable attribute-based key exchange (DABKE) framework that is resilient to impersonation attacks. We define the formal security models for DABKE framework, and propose a generic compiler that converts any attribute-based key exchanges into deniable ones. We prove that it can achieve session key security and user privacy in the standard model, and strong deniability in the simulation-based paradigm. In particular, the proposed generic compiler ensures: 1) a dishonest user cannot impersonate other user’s session participation in conversations since implicit authentication is used among authorized users; 2) an authorized user can plausibly deny his/her participation after secure conversations with others; 3) the strongest form of deniability is achieved using one-round communication between two authorized users.

A Shift from Model-Based to Simulation-Based Paradigm: Timeliness and Usefulness for Many Disciplines

Model-based paradigm has been adopted by a number of disciplines since its introduction in the late 70s. After a brief history on how model-based approach started in simulation, the merit and the spread of the model-based approach are described. The concept of model is subsumed in simulation, but many times employing just the model-based approach does not involve simulation. The superiority and advantages of simulation-based approach over model-based approach are manifold. This article describes the differences and advocates the use of simulation-based paradigm in advancing any computational discipline.

Simulation-based optimization of in–stream structures design: bendway weirs

Bendway weirs are one of the most practical in–stream rock structures utilized to protect the outer bend of meandering streams and rivers from erosion. We present development of a simulation-based paradigm for effective design of bendway weir structures to enhance meandering stream bank stability and control lateral migration. To do so, we employ the St. Anthony Falls Laboratory Virtual StreamLab (VSL3D) code to elucidate the flow and sediment transport phenomena induced by interaction of flow, mobile bed, and in–stream structures in large rivers under prototype conditions. We carried out numerous numerical experiments to systematically simulate various arrangements of bendway weir in two river test-beds and gaining insights into the physical mechanisms via which such bendway weirs modify turbulent flow, sediment transport and scour processes. The so-gained physical insights are then taken into account to develop a set of practical physics-based design criteria for optimal placement of bendway weirs in large rivers.

Oblivious decision program evaluation

In this study, the authors design efficient protocols for a number of ‘oblivious decision program (DP) evaluation’ problems. Consider a general form of the problem where a client who holds a private input interacts with a server who holds a private DP (e.g. a decision tree or a branching program) with the goal of evaluating his input on the DP without learning any additional information. Many known private database query problems such as symmetric private information retrieval and private keyword search can be formulated as special cases of this problem. Most of the existing works on the same problem focus on optimising communication. However, in some environments (supported by a few experimental studies), it is the computation and not the communication that may be the performance bottleneck. In this study, we design ‘computationally efficient’ protocols for the above general problem, and a few of its special cases. In addition to being one-round and requiring a small amount of work by the client (in the RAM model), the proposed protocols only require a small number of exponentiations (independent of the server's input) by both parties. The proposed constructions are, in essence, efficient and black-box reductions of the above problem to 1-out-of-2 oblivious transfer. It is proved that the proposed protocols secure (private) against ‘malicious’ adversaries in the standard ideal/real-world simulation-based paradigm.

Less is more: relaxed yet composable security notions for key exchange

Although they do not suffer from clear attacks, various key agreement protocols (for example that used within the TLS protocol) are deemed as insecure by existing security models for key exchange. The reason is that the derived keys are used within the key exchange step, violating the usual key-indistinguishability requirement. In this paper, we propose a new security definition for key exchange protocols that offers two important benefits. Our notion is weaker than the more established ones and thus allows the analysis of a larger class of protocols. Furthermore, security in the sense that we define enjoys rather general composability properties. In addition, our composability properties are derived within game-based formalisms and do not appeal to any simulation-based paradigm. Specifically, we show that for protocols, whose security relies exclusively on some underlying symmetric primitive, can be securely composed with key exchange protocols provided that two main requirements hold: (1) No adversary can break the underlying primitive, even when the primitive uses keys obtained from executions of the key exchange protocol in the presence of the adversary (this is essentially the security requirement that we introduce and formalize in this paper), and (2) the security of the protocol can be reduced to that of the primitive, no matter how the keys for the primitive are distributed. Proving that the two conditions are satisfied, and then applying our generic theorem should be simpler than performing a monolithic analysis of the composed protocol. We exemplify our results in the case of a profile of the TLS protocol.