The publish/subscribe paradigm makes IoT service collaborations more scalable and flexible, due to the space, time and control decoupling of event producers and consumers. Thus, the paradigm can be used to establish large-scale IoT service communication infrastructures such as Supervisory Control and Data Acquisition systems. However, preserving IoT service’s policy privacy is difficult in this paradigm, because a classical publisher has little control of its own event after being published; and a subscriber has to accept all the events from the subscribed event type with no choice. Few existing publish/subscribe middleware have built-in mechanisms to address the above issues. In this paper, we present a novel access control framework, which is capable of preserving IoT service’s policy privacy. In particular, we adopt the publish/subscribe paradigm as the IoT service communication infrastructure to facilitate the protection of IoT services policy privacy. The key idea in our policy-privacy solution is using a two-layer cooperating method to match bi-directional privacy control requirements: (a) data layer for protecting IoT events; and (b) application layer for preserving the privacy of service policy. Furthermore, the anonymous-set-based principle is adopted to realize the functionalities of the framework, including policy embedding and policy encoding as well as policy matching. Our security analysis shows that the policy privacy framework is Chosen-Plaintext Attack secure. We extend the open source Apache ActiveMQ broker by building into a policy-based authorization mechanism to enforce the privacy policy. The performance evaluation results indicate that our approach is scalable with reasonable overheads.
The reliability and stability of MEMS electrostatic comb resonators have become bottlenecks in practical applications. However, there are few studies that comprehensively consider the nonlinear dynamic behavior characteristics of MEMS systems and devices in a coupled field so that the related simulation accuracy is low and cannot meet the needs of design applications. In this paper, to avoid the computational complexity and the uncertainty of the results of three-field direct coupling and take into the damping nonlinearity caused by coupled fields, a novel electrostatic-fluid-structure three-field indirect coupling method is proposed. Taking an actual microcomb resonant electric field sensor as an example, an electrostatic-fluid-structure multiphysics coupling 3D finite element simulation model is established. After considering the influence of nonlinear damping concerning the large displacement of the structure and the microscale effect, multifield coupling dynamics research is carried out using COMSOL software. The multiorder eigenmodes, resonant frequency, vibration amplitude, and the distribution of fluid load of the microresonator are calculated and analyzed. The simulated data of resonance frequency and displacement amplitude are compared with the measured data. The results show that the fluid load distribution of the microelectrostatic comb resonator along the thickness direction is high in the middle and low on both sides. The viscous damping of the sensor under atmospheric pressure is mainly composed of the incompressible flow damping of the comb teeth, which is an order of magnitude larger than those of other parts. Compared with the measured data, it can be concluded that the amplitude and resonance frequency of the microresonator considering the nonlinear damping force and residual thermal stress are close to the experimental values (amplitude error: 15.47%, resonance frequency error: 12.48%). This article provides a reference for studies on the dynamic characteristics of electrostatically driven MEMS devices.
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