Blockchain is a kind of ‘ decentralized’ distributed ledger, which integrates asymmetric encryption algorithms, new distributed computing paradigms, consensus algorithms, smart contracts and other technologies. It has aroused extensive attention. However, since transaction records on the blockchain are publicly accessible to users, the ledger sharing mechanism is faced with serious privacy leaks. This paper aims to conduct comprehensive research on the privacy threats and protection mechanisms of blockchains. The concepts of identity privacy and transaction privacy in blockchain technology are introduced, the existing privacy protection mechanisms of the blockchain are classified, and their respective advantages and disadvantages are analyzed. In addition, some suggestions about future directions on blockchain privacy protection research are given.

The discrete logarithm problem ( DLP) is a research topic of great essence in algorithmic number theory, which also has diverse applications. In particular, the hardness of discrete logarithms underpins the securities of related cryptographic schemes. This article describes the basic version of DLP over a cyclic group of finite order and its variants, and surveys algorithms for discrete logarithms. First, generic algorithms are introduced, among which quantum algorithms can efficiently solve a certain class of DLP but classic algorithms occupy high time complexity. Then, the framework of index calculus method is presented, which has applications in accelerating algorithms for DLP in some specific scenario. At last, algorithms and progress for DLP over finite fields and elliptic curves are reported. DLP over finite fields is highly related with the characteristic of the finite field. Faster algorithms are designed for DLP over finite fields with small characteristics. In contrast, the state of the art algo rithms for general elliptic curve DLP run in exponential time.

Lattice public key cryptography is widely conceived as the most promising candidate in the quantum computing era due to the averagecase / hardcase equivalence of the underlying mathematic cally intractable problems, the linearity of the involved algebraic structures, and the tremendous cryp tographic functionalities. At present, numerous post quantum lattice cryptographic algorithms were deeloped to rely their securities on a lattice problem: the learning with errors ( LWE) problem. There fore, it is of vital significance to study the algorithms for solving the LWE problems to give insights in to the security of lattice public key cryptography. This paper firstly reviews and compares different solution strategies for distinct types of LWE problems. Secondly, we outline the basic ideas and technical principles of the existing lattice reduction algorithms. Finally, some prospections are made on the research focuses and trends in solving the LWE problems with lattice based reduction algorithms.

Zero knowledge proof allows the prover to prove the correctness of a statement to a verifier without revealing any other knowledge. At the theoretical level, this concept has a profound impact on cryptography and computer science. While at the application level, zero knowledge proof and its de rived verifiable computation provide data privacy protection and decentralization technology for the rapid development of financial technology represented by blockchain in recent years. In the last decade, the research on zero knowledge succinct non interactive arguments of knowledge ( zkSNARKs) has made remarkable progress, and it is widely used in the field of efinance by virtue of its simplicity and efficiency. This paper surveys the development process of zk SNARKs, and summarizes them ac cording to the different models they rely on.

In 5Gbased smart home systems, videos taken by smart cameras are usually uploaded to the cloud, which may lead to leakage of user privacy. Generally, a smart camera is a device with limited computing resources. Therefore, it is challenging to protect image privacy information while ensuring low latency transmission of video and certain availability of images. The traditional image privacy protection methods mainly employ design complex image encryption algorithms to encrypt the entire image. However, the privacy area in the image is usually only part of the image. If the entire image is encrypted, it is inflexible. At the same time, it will waste resources. At first, this paper used the YOLO v5 algorithm to pick up the sensitive areas based on a user definition, and then a masking algorithm is proposed to mask the sensitive areas based on DNA encryption technology and a VHE algorithm. The masking algorithm provides a dynamic masking strategy based on user needs. The algorithm is lightweight and flexible, and it can meet the needs of users for customizable privacy protection. Experiments prove that the scheme can be applied to the smart home environment.

Security of a network has always been a prominent issue. In a local network, the ARP protocol works at a lower level, and the security is often overlooked, and it is vulnerable to hacker at tacks. In the new network SDN architecture, ARP attacks are still a serious network security problem, and in this network architecture, not only the network terminal nodes will be exposed to the risk of at tacks, but also the controllers. Therefore, this article proposes an ARP attack solution based on the SDN architecture. This solution develops a defense module in the controller and an information verifi cation software in the host, and uses the controller to control network information to verify the host that needs ARP communication. If the verification is passed, the target host will reply to the ARP response message instead of the target host. If the verification fails, the ARP attack will be reported to the administrator. Experiments show that the scheme can effectively defend against various forms of ARP at tacks and effectively improve the security of a local area network.

In recent years, microwave absorbers with electromagnetic absorption characteristics have developed rapidly and received great attention. The application of microwave absorber in radar stealth and anti stealth is still an important topic in national defense research. In the recent published literatures, great progresses have been made in the study of metamaterial perfect absorbers, and their diversified development trend has been widely applied in industrial and military fields. This article focuses on the study of microwave absorbers to conduct a comprehensive review, first introducing the classification of the microwave absorbers, then introducing several kinds of microwave absorber structure, as well as some key applications of microwave absorbers. Meanwhile, this paper also introduces the preparation of microwave absorbers based on metamaterial surfaces. Finally, the future research di rection of microwave absorbers is discussed.

It is an effective approach to construct a Constant holistic Shadow ( CHS) space to improve the thermal comfort for peoples long period activities in outdoor public spaces in hot summer areas. However, in the relevant planning and design stages, it is necessary to conduct a set of spatiotemporal analyses on the conformity between the CHS space formed by the design and the target one required for crowd activities, to gradually promote the realization of the design of CHS space into the design process. In this paper, the spatiotemporal diversity and complexity of CHS space and its requirements for the design process were analyzed. The mode, object, standard, and characteristics of spatiotemporal analyses in the design of CHS space were expounded. And then, a framework of the analysis system has been established. It guides further exploration of the system of spatiotemporal analysis methods, to promote relevant planning and design to effectively construct CHS spaces.