期刊文献+
共找到328篇文章
< 1 2 17 >
每页显示 20 50 100
Secure Image Communication Using Galois Field,Hyper 3D Logistic Map,and B92 Quantum Protocol
1
作者 De Rosal Ignatius Moses Setiadi Nova Rijati +2 位作者 Ahmad Rofiqul Muslikh Bonifacius Vicky Indriyono Aceng Sambas 《Computers, Materials & Continua》 SCIE EI 2024年第12期4435-4463,共29页
In this paper,we propose a novel secure image communication system that integrates quantum key distribution and hyperchaotic encryption techniques to ensure enhanced security for both key distribution and plaintext en... In this paper,we propose a novel secure image communication system that integrates quantum key distribution and hyperchaotic encryption techniques to ensure enhanced security for both key distribution and plaintext encryption.Specifically,we leverage the B92 Quantum Key Distribution(QKD)protocol to secure the distribution of encryption keys,which are further processed through Galois Field(GF(28))operations for increased security.The encrypted plaintext is secured using a newly developed Hyper 3D Logistic Map(H3LM),a chaotic system that generates complex and unpredictable sequences,thereby ensuring strong confusion and diffusion in the encryption process.This hybrid approach offers a robust defense against quantum and classical cryptographic attacks,combining the advantages of quantum-level key distribution with the unpredictability of hyperchaos-based encryption.The proposed method demonstrates high sensitivity to key changes and resilience to noise,compression,and cropping attacks,ensuring both secure key transmission and robust image encryption. 展开更多
关键词 Galois field hyper 3D logistic map hyperchaotic map image security improved logistic map secure communication quantum security
下载PDF
Intelligent Reflecting Surface-Aided Secure and Covert Communications
2
作者 Zhou Xiaobo Jiang Yong +2 位作者 Xia Tingting Xia Guiyang Shen Tong 《China Communications》 SCIE CSCD 2024年第9期1-10,共10页
This work employs intelligent reflecting surface(IRS)to enhance secure and covert communication performance.We formulate an optimization problem to jointly design both the reflection beamformer at IRS and transmit pow... This work employs intelligent reflecting surface(IRS)to enhance secure and covert communication performance.We formulate an optimization problem to jointly design both the reflection beamformer at IRS and transmit power at transmitter Alice in order to optimize the achievable secrecy rate at Bob subject to a covertness constraint.We first develop a Dinkelbach-based algorithm to achieve an upper bound performance and a high-quality solution.For reducing the overhead and computational complexity of the Dinkelbach-based scheme,we further conceive a low-complexity algorithm in which analytical expression for the IRS reflection beamforming is derived at each iteration.Examination result shows that the devised low-complexity algorithm is able to achieve similar secrecy rate performance as the Dinkelbach-based algorithm.Our examination also shows that introducing an IRS into the considered system can significantly improve the secure and covert communication performance relative to the scheme without IRS. 展开更多
关键词 covert communications intelligent reflecting surface physical layer security reflection beamforming
下载PDF
Energy-efficient joint UAV secure communication and 3D trajectory optimization assisted by reconfigurable intelligent surfaces in the presence of eavesdroppers
3
作者 Huang Hailong Mohsen Eskandari +1 位作者 Andrey V.Savkin Wei Ni 《Defence Technology(防务技术)》 SCIE EI CAS CSCD 2024年第1期537-543,共7页
We consider a scenario where an unmanned aerial vehicle(UAV),a typical unmanned aerial system(UAS),transmits confidential data to a moving ground target in the presence of multiple eavesdroppers.Multiple friendly reco... We consider a scenario where an unmanned aerial vehicle(UAV),a typical unmanned aerial system(UAS),transmits confidential data to a moving ground target in the presence of multiple eavesdroppers.Multiple friendly reconfigurable intelligent surfaces(RISs) help to secure the UAV-target communication and improve the energy efficiency of the UAV.We formulate an optimization problem to minimize the energy consumption of the UAV,subject to the mobility constraint of the UAV and that the achievable secrecy rate at the target is over a given threshold.We present an online planning method following the framework of model predictive control(MPC) to jointly optimize the motion of the UAV and the configurations of the RISs.The effectiveness of the proposed method is validated via computer simulations. 展开更多
关键词 Unmanned aerial systems(UASs) Unmanned aerial vehicle(UAV) communication security Eaves-dropping Reconfigurable intelligent surfaces(RIS) Autonomous navigation and placement Path planning Model predictive control
下载PDF
Secure Communication via Chaotic Masking *
4
作者 纪飚 陆佶人 《Journal of Southeast University(English Edition)》 EI CAS 1998年第1期12-16,共5页
A novel secure communication approach via chaotic masking is proposed. At the transmitter, a message sequence is added to a chaotic masking sequence and is,at the same time, also involved in the generation of the mask... A novel secure communication approach via chaotic masking is proposed. At the transmitter, a message sequence is added to a chaotic masking sequence and is,at the same time, also involved in the generation of the masking sequence. At the receiver, a non dynamical system which adopts the same nonlinear functions as what is adopted at transmitter is used to retrieve the masking sequence from the received signal and then the message sequence is recovered through subtraction. The results of the theoretical analysis and computer simulation show that the chaotic digital secure communication system presented in this paper has the fine security, high reliability and can be implemented easily. 展开更多
关键词 CHAOS nonlinear discrete dynamical system secure communication
下载PDF
Cyber Resilience through Real-Time Threat Analysis in Information Security
5
作者 Aparna Gadhi Ragha Madhavi Gondu +1 位作者 Hitendra Chaudhary Olatunde Abiona 《International Journal of Communications, Network and System Sciences》 2024年第4期51-67,共17页
This paper examines how cybersecurity is developing and how it relates to more conventional information security. Although information security and cyber security are sometimes used synonymously, this study contends t... This paper examines how cybersecurity is developing and how it relates to more conventional information security. Although information security and cyber security are sometimes used synonymously, this study contends that they are not the same. The concept of cyber security is explored, which goes beyond protecting information resources to include a wider variety of assets, including people [1]. Protecting information assets is the main goal of traditional information security, with consideration to the human element and how people fit into the security process. On the other hand, cyber security adds a new level of complexity, as people might unintentionally contribute to or become targets of cyberattacks. This aspect presents moral questions since it is becoming more widely accepted that society has a duty to protect weaker members of society, including children [1]. The study emphasizes how important cyber security is on a larger scale, with many countries creating plans and laws to counteract cyberattacks. Nevertheless, a lot of these sources frequently neglect to define the differences or the relationship between information security and cyber security [1]. The paper focus on differentiating between cybersecurity and information security on a larger scale. The study also highlights other areas of cybersecurity which includes defending people, social norms, and vital infrastructure from threats that arise from online in addition to information and technology protection. It contends that ethical issues and the human factor are becoming more and more important in protecting assets in the digital age, and that cyber security is a paradigm shift in this regard [1]. 展开更多
关键词 Cybersecurity Information security Network security Cyber Resilience real-time Threat Analysis Cyber Threats Cyberattacks Threat Intelligence Machine Learning Artificial Intelligence Threat Detection Threat Mitigation Risk Assessment Vulnerability Management Incident Response security Orchestration Automation Threat Landscape Cyber-Physical Systems Critical Infrastructure Data Protection Privacy Compliance Regulations Policy Ethics CYBERCRIME Threat Actors Threat Modeling security Architecture
下载PDF
Achieving high-security and massive-capacity optical communications based on orbital angular momentum configured chaotic laser
6
作者 Yanwei Cui Jianguo Zhang +2 位作者 Zhongquan Nie Anbang Wang Yuncai Wang 《Advanced Photonics Nexus》 2024年第4期92-100,共9页
Secure and high-speed optical communications are of primary focus in information transmission.Although it is widely accepted that chaotic secure communication can provide superior physical layer security,it is challen... Secure and high-speed optical communications are of primary focus in information transmission.Although it is widely accepted that chaotic secure communication can provide superior physical layer security,it is challenging to meet the demand for high-speed increasing communication rate.We theoretically propose and experimentally demonstrate a conceptual paradigm for orbital angular momentum(OAM)configured chaotic laser(OAM-CCL)that allows access to high-security and massivecapacity optical communications.Combining 11 OAM modes and an all-optical feedback chaotic laser,we are able to theoretically empower a well-defined optical communication system with a total transmission capacity of 100 Gb∕s and a bit error rate below the forward error correction threshold 3.8×10^(-3).Furthermore,the OAM-CCL-based communication system is robust to 3D misalignment by resorting to appropriate mode spacing and beam waist.Finally,the conceptual paradigm of the OAM-CCL-based communication system is verified.In contrast to existing systems(traditional free-space optical communication or chaotic optical communication),the OAM-CCL-based communication system has threein-one characteristics of high security,massive capacity,and robustness.The findings demonstrate that this will promote the applicable settings of chaotic laser and provide an alternative promising route to guide high-security and massive-capacity optical communications. 展开更多
关键词 chaotic secure communication orbital angular momentum configured chaotic laser high security massive capacity MISALIGNMENT
下载PDF
Cutting-Edge Challenges in Communication Technology and Computer Network Security
7
作者 Haikang Gu 《Journal of Electronic Research and Application》 2024年第5期26-31,共6页
The rapid development of communication technology and computer networks has brought a lot of convenience to production and life,but it also increases the security problem.Information security has become one of the sev... The rapid development of communication technology and computer networks has brought a lot of convenience to production and life,but it also increases the security problem.Information security has become one of the severe challenges faced by people in the digital age.Currently,the security problems facing the field of communication technology and computer networks in China mainly include the evolution of offensive technology,the risk of large-scale data transmission,the potential vulnerabilities introduced by emerging technology,and the dilemma of user identity verification.This paper analyzes the frontier challenges of communication technology and computer network security,and puts forward corresponding solutions,hoping to provide ideas for coping with the security challenges of communication technology and computer networks. 展开更多
关键词 communication technology Computer network securITY
下载PDF
Quantum secure direct communication with quantum encryption based on pure entangled states 被引量:42
8
作者 李熙涵 李春燕 +3 位作者 邓富国 周萍 梁玉洁 周宏余 《Chinese Physics B》 SCIE EI CAS CSCD 2007年第8期2149-2153,共5页
This paper presents a scheme for quantum secure direct communication with quantum encryption. The two authorized users use repeatedly a sequence of the pure entangled pairs (quantum key) shared for encrypting and de... This paper presents a scheme for quantum secure direct communication with quantum encryption. The two authorized users use repeatedly a sequence of the pure entangled pairs (quantum key) shared for encrypting and decrypting the secret message carried by the travelling photons directly. For checking eavesdropping, the two parties perform the single-photon measurements on some decoy particles before each round. This scheme has the advantage that the pure entangled quantum signal source is feasible at present and any eavesdropper cannot steal the message. 展开更多
关键词 quantum secure direct communication quantum encryption quantum key pure entangled states
下载PDF
A two-step quantum secure direct communication protocol with hyperentanglement 被引量:18
9
作者 顾斌 黄余改 +1 位作者 方夏 张成义 《Chinese Physics B》 SCIE EI CAS CSCD 2011年第10期66-70,共5页
We propose a two-step quantum secure direct communication (QSDC) protocol with hyperentanglement in both the spatial-mode and the polarization degrees of freedom of photon pairs which can in principle be produced wi... We propose a two-step quantum secure direct communication (QSDC) protocol with hyperentanglement in both the spatial-mode and the polarization degrees of freedom of photon pairs which can in principle be produced with a beta barium borate crystal. The secret message can be encoded on the photon pairs with unitary operations in these two degrees of freedom independently. This QSDC protocol has a higher capacity than the original two-step QSDC protocol as each photon pair can carry 4 bits of information. Compared with the QSDC protocol based on hyperdense coding, this QSDC protocol has the immunity to Trojan horse attack strategies with the process for determining the number of the photons in each quantum signal as it is a one-way quantum communication protocol. 展开更多
关键词 quantum secure direct communication TWO-STEP hyperentanglement high capacity
下载PDF
Economical quantum secure direct communication network with single photons 被引量:10
10
作者 邓富国 李熙涵 +2 位作者 李春燕 周萍 周宏余 《Chinese Physics B》 SCIE EI CAS CSCD 2007年第12期3553-3559,共7页
In this paper a scheme for quantum secure direct communication (QSDC) network is proposed with a sequence of polarized single photons. The single photons are prepared originally in the same state (0) by the server... In this paper a scheme for quantum secure direct communication (QSDC) network is proposed with a sequence of polarized single photons. The single photons are prepared originally in the same state (0) by the servers on the network, which will reduce the difficulty for the legitimate users to check eavesdropping largely. The users code the information on the single photons with two unitary operations which do not change their measuring bases. Some decoy photons, which are produced by operating the sample photons with a Hadamard, are used for preventing a potentially dishonest server from eavesdropping the quantum lines freely. This scheme is an economical one as it is the easiest way for QSDC network communication securely. 展开更多
关键词 quantum secure direct communication NETWORK single photons
下载PDF
An efficient deterministic secure quantum communication scheme based on cluster states and identity authentication 被引量:10
11
作者 刘文杰 陈汉武 +3 位作者 马廷淮 李志强 刘志昊 胡文博 《Chinese Physics B》 SCIE EI CAS CSCD 2009年第10期4105-4109,共5页
A novel efficient deterministic secure quantum communication scheme based on four-qubit cluster states and single-photon identity authentication is proposed. In this scheme, the two authenticated users can transmit tw... A novel efficient deterministic secure quantum communication scheme based on four-qubit cluster states and single-photon identity authentication is proposed. In this scheme, the two authenticated users can transmit two bits of classical information per cluster state, and its efficiency of the quantum communication is 1/3, which is approximately 1.67 times that of the previous protocol presented by Wang et al [Chin. Phys. Lett. 23 (2006) 2658]. Security analysis shows the present scheme is secure against intercept-resend attack and the impersonator's attack. Furthermore, it is more economic with present-day techniques and easily processed by a one-way quantum computer. 展开更多
关键词 deterministic secure quantum communication cluster state identity authentication
下载PDF
Fault tolerant quantum secure direct communication with quantum encryption against collective noise 被引量:9
12
作者 黄伟 温巧燕 +2 位作者 贾恒越 秦素娟 高飞 《Chinese Physics B》 SCIE EI CAS CSCD 2012年第10期101-109,共9页
We present two novel quantum secure direct communication(QSDC) protocols over different collective-noise channels.Different from the previous QSDC schemes over collective-noise channels,which are all source-encrypti... We present two novel quantum secure direct communication(QSDC) protocols over different collective-noise channels.Different from the previous QSDC schemes over collective-noise channels,which are all source-encrypting protocols,our two protocols are based on channel-encryption.In both schemes,two authorized users first share a sequence of EPR pairs as their reusable quantum key.Then they use their quantum key to encrypt and decrypt the secret message carried by the decoherence-free states over the collective-noise channel.In theory,the intrinsic efficiencies of both protocols are high since there is no need to consume any entangled states including both the quantum key and the information carriers except the ones used for eavesdropping checks.For checking eavesdropping,the two parties only need to perform two-particle measurements on the decoy states during each round.Finally,we make a security analysis of our two protocols and demonstrate that they are secure. 展开更多
关键词 quantum cryptography quantum secure direct communication quantum encryption collective noise
下载PDF
Mobile Jammer-Aided Secure UAV Communications via Trajectory Design and Power Control 被引量:13
13
作者 An Li Wenjing Zhang 《China Communications》 SCIE CSCD 2018年第8期141-151,共11页
To further promote the achievable average secrecy rate for UAV-ground communications, a UAV-aided mobile jamming strategy was proposed in this paper. Specifically, an additional cooperative UAV is employed as a mobile... To further promote the achievable average secrecy rate for UAV-ground communications, a UAV-aided mobile jamming strategy was proposed in this paper. Specifically, an additional cooperative UAV is employed as a mobile jammer to transmit the jamming signal to help keep the source UAV closer to the ground destination, thus establishing more favorable legitimate link and enhancing the secrecy performance. We aimed to maximize the achievable secrecy rate by jointly optimizing the trajectories and transmit power of both source UAV and jammer UAV. To solve the considered non-convex optimization problem, we presented a block coordinate descent based iterative algorithm to address a sequence of approximated convex problems for the optimized parameter block by block to find a local optimal solution. Numerical results verify that the proposed algorithm can achieve significant secrecy rate gain compared to all the benchmark schemes. 展开更多
关键词 physical layer security UAV-ground communications mobile jammer-aided trajectory design power control
下载PDF
Quantum Secure Direct Communication by Using Three-Dimensional Hyperentanglement 被引量:8
14
作者 施锦 龚彦晓 +2 位作者 徐平 祝世宁 詹佑邦 《Communications in Theoretical Physics》 SCIE CAS CSCD 2011年第11期831-836,共6页
We propose two schemes for realizing quantum secure direct communication (QSDC)by using a set ofordered two-photon three-dimensional hyperentangled states entangled in two degrees of freedom (DOFs)as quantuminformatio... We propose two schemes for realizing quantum secure direct communication (QSDC)by using a set ofordered two-photon three-dimensional hyperentangled states entangled in two degrees of freedom (DOFs)as quantuminformation channels.In the first scheme,the photons from Bob to Alice are transmitted only once.After insuring thesecurity of the quantum channels,Bob encodes the secret message on his photons.Then Alice performs single-photontwo-DOF Bell bases measurements on her photons.This scheme has better security than former QSDC protocols.In thesecond scheme,Bob transmits photons to Alice twice.After insuring the security of the quantum channels,Bob encodesthe secret message on his photons.Then Alice performs two-photon Bell bases measurements on each DOF.The schemehas more information capacity than former QSDC protocols. 展开更多
关键词 quantum secure direct communication hyperentanglement Bell bases measurement
下载PDF
Energy-Efficient Trajectory Planning for UAV-Aided Secure Communication 被引量:13
15
作者 Qian Wang Zhi Chen Hang Li 《China Communications》 SCIE CSCD 2018年第5期51-60,共10页
Wireless communication with unmanned aerial vehicles(UAVs) has aroused great research interest recently. This paper is concerned with the UAV's trajectory planning problem for secrecy energy efficiency maximizatio... Wireless communication with unmanned aerial vehicles(UAVs) has aroused great research interest recently. This paper is concerned with the UAV's trajectory planning problem for secrecy energy efficiency maximization(SEEM) in the UAV communication system. Specifically, we jointly consider the secrecy throughput and UAV's energy consumption in a three-node(fixed-wing UAV-aided source, destination, and eavesdropper) wiretap channel. By ignoring the energy consumption on radiation and signal processing, the system's secrecy energy efficiency is defined as the total secrecy rate normalized by the UAV's propulsion energy consumption within a given time horizon. Nonetheless, the SEEM problem is nonconvex and thus is intractable to solve. As a compromise, we propose an iterative algorithm based on sequential convex programming(SCP) and Dinkelbach's method to seek a suboptimal solution for SEEM. The algorithm only needs to solve convex problems, and thus is computationally efficient to implement. Additionally, we prove that the proposed algorithm has Karush-KuhnTucker(KKT) point convergence guarantee. Lastly, simulation results demonstrate the efficacy of our proposed algorithm in improving the secrecy energy efficiency for the UAV communication system. 展开更多
关键词 physical layer security UAV-aided communications secrecy energy efficiency trajectory planning
下载PDF
An efficient quantum secure direct communication scheme with authentication 被引量:7
16
作者 杨宇光 温巧燕 朱甫臣 《Chinese Physics B》 SCIE EI CAS CSCD 2007年第7期1838-1842,共5页
In this paper an efficient quantum secure direct communication (QSDC) scheme with authentication is presented, which is based on quantum entanglement and polarized single photons. The present protocol uses Einstein-... In this paper an efficient quantum secure direct communication (QSDC) scheme with authentication is presented, which is based on quantum entanglement and polarized single photons. The present protocol uses Einstein-Podolsky-Rosen (EPR) pairs and polarized single photons in batches. A particle of the EPR pairs is retained in the sender's station, and the other is transmitted forth and back between the sender and the receiver, similar to the‘ping-pong' QSDC protocol. According to the shared information beforehand, these two kinds of quantum states are mixed and then transmitted via a quantum channel. The EPR pairs are used to transmit secret messages and the polarized single photons used for authentication and eavesdropping check. Consequently, because of the dual contributions of the polarized single photons, no classical information is needed. The intrinsic efficiency and total efficiency are both 1 in this scheme as almost all of the instances are useful and each EPR pair can be used to carry two bits of information. 展开更多
关键词 quantum key distribution quantum authentication quantum secure direct communication non-orthogonal
下载PDF
Study of dual-directional high rate secure communication systems using chaotic multiple-quantum-well lasers 被引量:4
17
作者 颜森林 《Chinese Physics B》 SCIE EI CAS CSCD 2007年第11期3271-3278,共8页
A scheme of synchronized injection multi-quantum-well (MQW) laser system using optical couphng-feedback is presented for performing chaotic dual-directional secure communication. The performance characterization of ... A scheme of synchronized injection multi-quantum-well (MQW) laser system using optical couphng-feedback is presented for performing chaotic dual-directional secure communication. The performance characterization of chaos masking is investigated theoretically, the equation of synchronization demodulation is deduced and its root is also given. Chaos masking encoding with a rate of 5 Gbit/s and a modulation frequency of 1 GHz, chaos modulation with a rate of 0.2 Gbit/s and a modulation frequency of 0.2 GHz and chaos shifting key with a rate of 0.2 Gbit/s are numerically simulated, separately. The ratio of the signal to the absolute synchronous error and the time for achieving synchronous demodulation are analysed in detail. The results illustrate that the system has stronger privacy and good performances so that it can be applied in chaotic dual-directional high rate secure communications. 展开更多
关键词 CHAOS MQW laser secure dual-directional communication
下载PDF
Bidirectional Quantum Secure Direct Communication Network Protocol with Hyperentanglement 被引量:4
18
作者 顾斌 黄余政 +1 位作者 方夏 陈玉林 《Communications in Theoretical Physics》 SCIE CAS CSCD 2011年第10期659-663,共5页
We propose a bidirectional quantum secure direct communication(QSDC) network protocol with the hyperentanglment in both the spatial-mode ad the polarization degrees of freedom of photon pairs which can in principle be... We propose a bidirectional quantum secure direct communication(QSDC) network protocol with the hyperentanglment in both the spatial-mode ad the polarization degrees of freedom of photon pairs which can in principle be produced with a beta barium borate crystal.The secret message can be encoded on the photon pairs with unitary operations in these two degrees of freedom independently.Compared with other QSDC network protocols,our QSDC network protocol has a higher capacity as each photon pair can carry 4 bits of information.Also,we discuss the security of our QSDC network protocol and its feasibility with current techniques. 展开更多
关键词 quantum secure direct communication NETWORK BIDIRECTIONAL hyperentanglement high capacity
下载PDF
Quantum Secure Communication Scheme with W State 被引量:6
19
作者 WANG Jian ZHANG Quan TANG Chao-Jing 《Communications in Theoretical Physics》 SCIE CAS CSCD 2007年第4X期637-640,共4页
We present a quantum secure communication scheme using three-qubit W state. It is unnecessary for the present scheme to use alternative measurement or Bell basis measurement. Compared with the quantum secure direct co... We present a quantum secure communication scheme using three-qubit W state. It is unnecessary for the present scheme to use alternative measurement or Bell basis measurement. Compared with the quantum secure direct communication scheme proposed by Cao et at. [H.J. Cao and H.S. Song, Chin. Phys. Lett. 23 (2006) 290], in our scheme, the detection probability for an eavesdropper's attack increases from 8.3% to 25%. We also show that our scheme is secure for a noise quantum channel. 展开更多
关键词 quantum secure communication W state
下载PDF
Controlled Secure Direct Communication Protocol via the Three-Qubit Partially Entangled Set of States 被引量:7
20
作者 Gang Xu Ke Xiao +2 位作者 Zongpeng Li Xin-Xin Niu Michael Ryan 《Computers, Materials & Continua》 SCIE EI 2019年第3期809-827,共19页
In this paper,we first re-examine the previous protocol of controlled quantum secure direct communication of Zhang et al.’s scheme,which was found insecure under two kinds of attacks,fake entangled particles attack a... In this paper,we first re-examine the previous protocol of controlled quantum secure direct communication of Zhang et al.’s scheme,which was found insecure under two kinds of attacks,fake entangled particles attack and disentanglement attack.Then,by changing the party of the preparation of cluster states and using unitary operations,we present an improved protocol which can avoid these two kinds of attacks.Moreover,the protocol is proposed using the three-qubit partially entangled set of states.It is more efficient by only using three particles rather than four or even more to transmit one bit secret information.Given our using state is much easier to prepare for multiqubit states and our protocol needs less measurement resource,it makes this protocol more convenient from an applied point of view. 展开更多
关键词 Controlled secure direct communication cluster state three-qubit partially entangled state entanglement swapping.
下载PDF
上一页 1 2 17 下一页 到第
使用帮助 返回顶部