Search

SM2, issued by China in 2010, is a public key cryptography standard based on elliptic curves.It has been widely used in finance, social security and other fields thanks to its advantages of improved signature efficiency, decreased storage space and computing complexity than RSA.With the popularization and application of SM2, the issues of its key security and data privacy are of great concern.The single-key mode inhibits the potential application in multi-user settings, and the leakage of the key will threaten the security of the entire cryptosystem due to the centralization.The problem of secure storage and reasonable utilization of keys needs to be solved urgently.In addition, the SM2 digital signature algorithm cannot guarantee the message privacy.Aiming at the issues of key security and data privacy of the signature algorithm, many researchers have proposed the idea of cooperative signature and blind signature for SM2.However, there isn’t SM2 collaborative blind signature scheme proposed.Then a two-party cooperative blind signing protocol based on SM2 was proposed in this paper, which allowed two parties to sign except the user.The signing process did not require recovering the complete private key, while not revealing the information of the partial private key and secret number.The key was stored separately to improve the security of the key, while the blind signature protected the privacy of the message.In terms of security, the protocol satisfied unforgeability and unlinkability.The protocol was implemented using C to demonstrate the efficiency of each participant’s local operation.In the honest model, the time cost of each entity in the cooperative signature phase was similar as that of executing a lightweight SM2 blind signature.Overall, the proposed protocol has certain advantages in terms of function and efficiency.

The isolated DC/DC converter plays an irreplaceable role in the development of the DC microgrid. However, the multiple discrete high‐frequency transformers occupy considerable volume in power converters due to the connection of multiple isolated converters. In order to reduce the number of discrete transformers and increase the power density as well as the reliability of the power converter, a three‐port isolated DC/DC converter with a decoupling magnetic integrated high‐frequency transformer (DMIHFT) is proposed for the DC microgrid in this paper. The semiconductor count of the proposed converter is reduced by combining one DAB converter and two LLC converters. Three discrete transformers are integrated into a single common core, and magnetic decoupling is achieved among each transformer by rational design at the same time. In addition, the magnetic circuit model derivation process of the proposed DMIHFT and the operation principles of the converter are described in detail. The design guidance of the proposed DMIHFT is present. And then, a 15 kW/20 kHz DMIHFT is designed based on the design guideline, and the simulation is carried out. Finally, a 15 kW/20 kHz DMIHFT prototype is fabricated, and the effectiveness of the proposed DMIHFT is verified by experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes an LLC‐DAB integrated high‐frequency isolated DC–DC converter topology structure to reduce the loss and cost of the DC power distribution system. Furthermore, the complexity and efficiency of the system also can be improved. The proposed converter consists of a DAB converter and two input‐parallel‐output‐parallel half‐bridge LLC resonant converters. It provides two DC voltage level buses, namely the HVDC bus and the LVDC bus. Compared with the typical converter topology of the DC power distribution system, the number of power semiconductors of the proposed converter topology is reduced by sharing the power semiconductors of the DAB converter and LLC resonant converter. As a result, with the number of power semiconductors decreasing, the cost and loss of the system are reduced. Moreover, the proposed converter can control the flow direction of power conversion and supply power to the loads. The single‐phase‐shift modulation method is adopted for the DAB converter, and two LLC resonant converters operate as the DC transformer under resonant frequency with open‐loop control. The operation principles and characteristics of the proposed converter are discussed. Finally, the simulation is carried out and an experimental prototype is developed to verify the effectiveness of the proposed topology. [ABSTRACT FROM AUTHOR]

A novel monohedral permanent magnet (PM) configuration is suggested and geometrically optimized to have higher magnetic efficiency as well as higher degree of access to imaging region of a magnetic resonance imaging (MRI) system. The configuration has a pair of main PMs magnetized in the opposite directions, respectively. The geometry of the main PMs is optimized by using genetic algorithm combined with a novel flexible magnetic field analysis method which combines finite-element method and new-type equivalent source method. Through an optimal design, the suggested PM configuration is proven to provide a sufficiently homogeneous and strong magnetic field for MRI application. Index Terms--Finite element method (FEM), magnetic resonance imaging (MRI), monohedral permanent magnet (PM), new-type equivalent source method (NESM).

In magnetic resonance imaging (MRI) magnets, field shimming technique is, in general, necessary to increase the field homogeneity in imaging region to an acceptable level after manufacturing. This paper presents a novel passive shimming method using permanently magnetized shimming pieces. In the method, the shimming design is modeled as an integer programming problem, and the distribution of shimming pieces is optimized. Through an application to a 0.3-T permanent magnet MRI system, the optimally designed shimming pieces are proven to improve the field homogeneity from 1456 to 784 ppm after just one iteration of shimming courses is carried out. Index Terms--Integer programming, magnetic resonance imaging (MRI), optimization, permanent magnet (PM).

A combined method is presented to deal with the practical engineering problems of multiobjective optimization. The Nondominated Sorting Genetic Algorithm II (NSGA-II) is adopted as a searching tool for the Pareto-optimal solutions, which is improved by using a new crossover operator. The response surface model (RSM) based on the radial basis function is used to reduce the computational effort. The application of the method to the shape optimization process of a permanent magnet assembly for magnetic resonance imaging devices is described, and the numerical results show that the method is feasible and efficient for the engineering shape optimization. Index Terms--Genetic algorithm, main magnet of MRI, multiobjective optimization, shape optimization.

This paper presents a new 3-D finite-element method for taking account of vector hysteresis and anisotropy. The proposed method combines the improved scalar Preisach model with the lagging angle between magnetic flux density and magnetic field intensity to solve vector hysteresis problem. Magnetic material's B - H curves with any other directions to rolling direction are obtained by interpolating the measured B - H curves to solve anisotropy problem. The method enables us to solve vector hysteresis and anisotropy problem simply. In order to validate the algorithm presented, TEAM problem32 has been analyzed using 3-D FEM as an example. Index Terms--Anisotropy, lagging angle, Preisach hysteresis model, vector hysteresis.

This paper presents a method to simulate the characteristics of permanent magnet materials with a magnetic field varying arbitrarily. Combining Preisach model and finite element analysis, a dynamic magnetic field computation is implemented for a permanent magnet assembly in a process of assembling. The hysteresis characteristic including local loop and rotational magnetization are considered in the formulation of the method proposed. The numerical results are compared with the ones of a conventional method, the electric current sheet equivalent, and the measured values to verify the validity of the presented method. Index Terms--Finite element method, magic ring, Preisach hysteresis model, rotational magnetization.