杨志贤.蓝牙技术及其安全性的研究3.0206240813
收藏
资源目录
压缩包内文档预览：
编号：52210822
类型：共享资源
大小：930.88KB
格式：RAR
上传时间：2020-02-28
上传人：qq77****057
认证信息
个人认证
李**（实名认证）
江苏
IP属地：江苏
25
积分
- 关 键 词：
-
杨志贤
蓝牙技术
及其
安全性
研究
3.0206240813
- 资源描述：
-
杨志贤.蓝牙技术及其安全性的研究3.0206240813,杨志贤,蓝牙技术,及其,安全性,研究,3.0206240813
- 内容简介：
-
毕业设计说明书蓝牙技术及其安全性的研究作 者:杨志贤学 号：0206240813学院(系):信息与通信工程学院通信工程系专 业:通信工程讲师刘双峰指导教师： 评 阅 人： 2006 年06 月中北大学2006届本科毕业设计说明书蓝牙技术及其安全性的研究摘要蓝牙技术是一种无线数据与语音通信的开放性规范，它以低成本的近距离无线连接为基础，为固定与移动设备通信环境建立一种无线连接。蓝牙提供了短距离的对等层之间的通信技术，支持点对点的无线数据通信，在现代通信过程中，在保证数据传送的实时性和正确性的同时，怎样避免数据被非法窃取或是数据被攻击的问题显得尤为重要。为了实现对用户数据的保护和信息的保密性，蓝牙系统在应用层和链路层提供了安全措施，这些措施适合对等的环境，即在每个蓝牙设备使用鉴权和加密过程。蓝牙的鉴权和加密操作在蓝牙系统的安全性方面起着关键作用，严密的算法体制保证鉴权和加密操作的准确性和高速性，有效的保护了用户的通信数据。蓝牙技术可以采用软件和硬件的方式实现安全层的密钥生成和鉴权过程。本文只是对蓝牙安全问题进行了一系列的理论探讨和研究关键字:蓝牙, 鉴权, 加密 The Research of bluetooth technology and security Abstract Bluetooth Technology is a kind of open specification for wireless data voice. It bases on low cost short-range radio link, and it can build a wireless link and for fixed and mobile device.Bluetooth is designed as a wireless cable replacement to connect a wide range of devices. It provides a short range, peer-to-peer wireless communication between two units. It s important to avoid the data been attacked or stolen the same time we ensure the data is transferred correctly. To realize data encryption and communication protection, Bluetooth system provides encryption in application layer and link layer. These operation including authentication and encryption is used by and each Bluetooth device and executed in the equal layer. Unassailable algorithm protects data and ensures the operations execute correctly and rapidly. Bluetooth can implement its security layers key generation mechanism and authentication in software or hardware. This article only was has carried on a series of theories discussion and the research to the Bluetooth security problem. Keywords: Bluetooth , authertication , encryption 中北大学2006届本科毕业设计说明书How Bluetooth WorksChatschik BisdikianThere are lots of different ways that electronic devices can connect to one another. For example:Many desktop computer systems have a CPU unit connected to a mouse, a keyboard, a printer and so on. A personal digital assistant (PDA) will normally connect to the computer with a cable and a docking cradle. A TV will normally connect to a VCR and a cable box, with a remote control for all there components. A cordless phone connects to its base unit radio waves and it may have a headset that connects to the phone with a wire. In a stereo system, a CD player and other audio devices connect to the receiver, which connects to the speakers. When you use computers, entertainment systems or telephones, the various pieces and parts of the systems make up a community of electronic devices. These devices communicate with each other using a variety of wires, cables, radio signals and infrared light beams, and an even greater variety of connectors, plugs and protocols.The art of connecting things is becoming more and more complex every day. We sometimes feel as if we need a Ph.D. in electrical engineering just to set up the electronics in our homes! In this article, we will look at a completely different way to form the connections, called Bluetooth. Bluetooth is wireless and automatic, and has a number of interesting features that can simplify our daily lives.The ProblemsWhen any two devices need to talk to each other, they have to agree on a number of points before the conversation can begin. The first point of agreement is physical: Will they talk over wires, or through some form of wireless signals? If they use wires, how many are required one, two, eight, 25? Once the physical attributes are decided, several more questions arise:Information can be sent 1 bit at a time in a scheme called parallel communications, or in groups of bits (usually 8 or 16 at a time) in a scheme called parallel communications. . A desktop computer uses both serial and parallel communications to talk to different devices: Modems, mice and keyboards tend to talk through serial links, while printers tend to use parallel links.All of the parties in an electronic discussion need to know what the bits mean and whether the message they receive is the same message that was sent. In most cases, this means developing a language of commands and responses know as a protocol. Some types of products have a standard protocol used by virtually all companies so that the commands for one product will tend to have the same effect on another. Modems fall into this category. Other product types each speak their own language, which means that commands intended for one specific product will seem gibberish if received by another. Printers are like this, with multiple standards like PCL and PostScript.Companies that manufacture computers, entertainment systems and other electronic devices have realized that the incredible array of cables and connectors involved in their products makes it difficult for even expert technicians to correctly set up a complete system on the first try. Setting up computer and home entertainment system becomes terrifically complicated when the person buying the equipment has to learn and remember all the details to connect all the parts. In order to make home electronic more user friendly, we need a better way for all the electronic part of our modern life to talk to each other. Thats where Bluetooth comes in.Bluetooth BasicsBluetooth is a standard developed by a group of electronics manufacturers that allows any sort of electronic equipment from computer and cell phones to keyboards and headphones to make its own connections, without wires, cables or any direct action from a user. Bluetooth is intended to be a standard that works at two levels: It provides agreement at the physical level Bluetooth is a radio-frequency standard . It also provides agreement at the next level up , where products have to agree on when bits are sent, how many will be sent at a time and how the parties in conversation can be sure that the message received is same as the message sent.The companies belonging to the Bluetooth Special Interest Group, and there are more than 1,000 of them, want to let Bluetooths radio communications take the place of wires for connecting peripherals, telephones and computers.Other Wireless ConnectionsThere are already a couple of ways to get around using wires. One is to carry information between computers via beams of light in the infrared spectrum. Infrared refers to light waves of a lower frequency than human eyes can receive and interpret. Infrared is used in most television remote control systems, and with a standard called IrDA (Infrared Data Association) its used to connect some computers with peripheral devices. For most of these computer and entertainment purposes, infrared is used in a digital mode the signal is pulsed on and off very quickly to send data from one point to another.Infrared communications are fairly reliable and dont cost very much to build into a device, but there are a couple of drawbacks. First, infrared is a “line of sight” technology. For example, you have to point the remote control at the television or DVD player to make things happen. The second drawback is that infrared is almost always a “one to one” technology. You can send data between your desktop computer and your laptop computer, but not your laptop computer and your PDA at the time.These two qualities of infrared are actually advantageous in some regards. Because infrared transmitters and receivers have to be lined up with each other, interference between devices is uncommon. The one-to-one nature of infrared communications is useful in that you can make sure a message goes only to the intended recipient, even in a room full infrared receivers.The Bluetooth Solution Bluetooth is intended to get around the problems that come with both infrared and cable synchronizing systems. The hardware vendors, which include Siemens, Intel, Toshiba, Motorola and Ericsson, have developed a specification for a very small radio module to be built into computer, telephone and entertainment equipment. From the users point of view, there are three important features to Bluetooth: Its wireless. When you travel, you dont have to worry about keeping track of a briefcase full of cables to attach all of your components, and you can design your office without wondering where all the wires will go.Its inexpensive.You dont have to think about it. Bluetooth doesmt require you to do anything special to make it work. The devices find one another and strike up a conversation without any user input at all.Bluetooth FrequencyBluetooth communicates on a frequency of 2.45 gigahertz, which has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).A number of devices that you may already use take advantage of this same radio-frequency band. Baby monitors, garage-door openers and the newest generation of cordless phones all make use of frequencies in the ISM band. Making sure that Bluetooth and these other devices dont interfere with one another has been a crucial part of the design process.Avoiding Interference: Low PowerOne of the ways Bluetooth devices avoid interfering with other system is by sending out very weak signals of 1 milliwatt. By computer, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters, cutting the chances of interference between your computer system and your portable telephone or television. Even with the low power, the walls in your house wont stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms.With many different Bluetooth devices in a room, you might think theyd interfere with one another, but its unlikely. On the next page, well see why.Avoiding Interference: Hopping It is unlikely that several devices will be on the same frequency at the same time, because Bluetooth uses a technique called spread-spectrum frequency hopping. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the casa of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second. When Bluetooth-capable devices come within range of one another, an electronic conversation takes place to determine whether they have data to share or whether one needs to control the other. The user doesnt have to press a button or give a command the electronic conversation happens automatically. Once the conversation has occurred, the devices whether theyre part of a computer system or a stereo form a network. Bluetooth systems create a personal-area network (PAN), or piconet, that may fill a room or may encompass no more distance than that between the cell phone on a belt-clip and the headset on your head. Once a piconet is established, the members randomly hop frequencies in unison so they stay in touch with one another and avoid other piconets that mat be operating in the same room.Example: NetworksLets take a look at how the Bluetooth frequency hopping and personal-area network keep system from becoming confused. Lets say youre got a typical modern living room with the typical modern stuff inside. Theres an entertainment system with a stereo, a DVD player, a satellite TV receiver and a television; theres cordless telephone and a personal computer. Each of these systems uses Bluetooth, and each forms its own piconet to talk between main unit and peripheral.The cordless telephone has one Bluetooth transmitter in the base and another in the handset. The manufacturer has programmed each unit with an address that falls into a range of addresses it has established for a particular type of device. When the base is first turned on, it sends radio signals asking for a response from any units with an address in a particular range. Since the handset has an address in the range, it responds, and a tiny network is formed. Now, even if one of these devices should receive a signal from another system, it will ignore it since its not from within the network. The computer and entertainment system go through similar routines, establishing networks among address in ranges established by manufacturers. Once the networks are established, the systems begin talking among themselves. Each piconet hops randomly through the available frequencies, so all of the piconets are completely separated from one another. Now the living room has three separate network established , each one made up of devices that know the address of transmitters it should listen to and the address of receivers it should talk to.Since each network is changing the frequency of its operation thousand of times a second, its unlikely that any two network will be on the same frequency at the same time. If it turns out that they are, then the resulting confusion will only cover a tiny fraction of a second, and software designed to correct for such errors weeds out the confusing information and gets on with networks business Example:Half/Full Duplex Most of the time,a network or communications method either works in one direction at a time, called half-duplex communication, or in both direction simultaneously, called full-duplex communication. A speakerphone that lets you either listen or talk, but not both ,is an example of half-duplex communication, while a regular telephone handset is a full-duplex device.Beacause Bluetooth is designed to work in a number of different circumstances, it can be either half-duplex or full-duplex. The cordless telephone is an example of a use that will call for a full-duplex (two-way) link, and Buletooth can send data at more than 64,000 bits per second in a full-duplex linka rate high enough to support several human voice conversation. If a particular use calls for a half-duplex linkconnecting to a computer printer, for exampleBluetooth can transmit up to 721 kilobits per second(Kbps) in one direction,with 57.6 Kps in the other. If the use calls for the same speed in both directions, a link with 432.6-Kbps capacity in each direction can be made.Bluetooth Space Here are some specification details from the Bluetooth Web siteThe devices in a piconet share a common communication data channel. The channel has a total capacity of 1 megabit per second (Mbps). Headers and handshaking information consume about 20 percent of this capacity.In the United States and Europe, the frequency range is 2,400 to 2,483.5 MHz, with 79 1-MHz radio frequency (RF) channels. In practice, the range is 2,402 MHz to 2,480 MHz. In Japan, the frequency range is 2,497 MHz with 23 1-MHz rf channels.A data channel hops randomly 1,600 times per second between the 79 (or 23) RF channels.Each channel is divided into time slots 625 microseconds long.A piconet has a master and up to seven slzves.Packets can be up to five time slots wide.Data in a packet can be up to 2,745 bits in length.There are currently two types of data transfer between devices: SCO ( synchronous connection oriented) and ACL (asynchronous connectionless).In a piconet, there can be up to three SCO links of 64,000 bits per second each. To avoid timing and collision problems, the SCO links use reserved slots set up by the master.Masters can support up to three SCO links with one, two or three slaves.One master and slave can have a single ACL link.ACL is either point-to-point (master to one slave) or broadcast to all the slaves.ACL slaves can only transmit when requested by the master. The heart of the Bluetooth specification is the Bluetooth protocol stack. By providing well-defined layers of functionality, the Bluetooth specification ensures interoperability of Bluetooth devices and encourages adoption of Bluetooth technology.As you can see in figure 1-1, these layers range from the low-level radio link to the profiles.Figure 1-1：The Bluetooth protocol stackLower LayersAt the base of the Bluetooth protocol stack is the radio layer. The radio module in a Bluetooth device is responsible for the modulation and demodulation of data into RF signals for transmission in the air. The radio layer describes the physical characteristics a Bluetooth devices receiver-transmitter component must have. These include modulation characteristics, radio frequency tolerance, and sensitivity level.Above the radio layer is the baseband and link controller layer. The Bluetooth specification doesnt establish a clear distinction between the responsibilities of the baseband and those of the link controller. The best way to think about it is that the baseband portion of the layer is responsible for properly formatting data for transmission to and from the radio layer. In addition, it handles the synchronization of links. The link controller portion of this layer is responsible for carrying out the link managers commands and establishing and maintaining the link stipulated by link manager.The link manager itself translates the host controller interface (HCI) commands it receives into baseband-level operations. It is responsible for establishing and configuring links and managing power-change requests, among other tasks.Youve noticed links mentioned numerous time in the preceding paragraphs. The Bluetooth specification defines two types of links between Bluetooth devices:Synchronous, Connection-Oriented (SCO), for isochronous and voice communication using, for example, headsetsAsynchronous, Connectionless (ACL), for data communication, such as the exchange of vCards.Each link type is associated with a specific packet. A SCO link provides reserved channel bandwidth for communication between a master and a slave, and supports regular, periodic exchange of data with no retransmission of SCO packets.An ACL link exists between a master and a slave the moment a connection is established. The data packets Bluetooth uses for ACL links all have 142 bits of encoding information in addition to a payload that can be as large as 2712 bits. The extra amount of data encoding heightens transmission security. It also helps to maintain a robust communication link in an environment fill with other devices and common noise.The HCI (host controller interface) layer acts as a boundary between the lower layers of the Bluetooth protocol stack and upper layers The Bluetooth specification defines a standard HCI to support Bluetooth systems that are implemented across two separate processors, For example, a Bluetooth system on computer might use a Bluetooth modules processor to implement the lower layers of the stack (radio, baseband, link controller, and link manager). It might then use its own processor to implement the upper layers (L2CAP, RFCOMM, OBEX, and selected profiles). In this scheme, the lower portion is known as the Bluetooth module and the upper portion as the Bluetooth host.Of course, its not required to partition the Bluetooth stack in this way. Bluetooth headsets, for example, combine the module and the host portions of stack on one processor because they need to be small and self-contained. In such devices, the HCI may not be implemented at all unless at all unless device testing is required.Because the Bluetooth HCI is well defined, you can write drivers that handle different Bluetooth modules from different manufacturers. Apple provides an HCI controller object that supports a USB implementation of the HCI layer. . ReferencesBN. Sklavos et al., Random Number Generator Architecture and VLSIImplementation,Proc. IEEE Int1 Symp. Circuits &Systems (ISCAS 02), IEEE Circuits and Systems So Bluetooth security white paper;Bluetooth SIG security expert group.c. Press, Piscataway, N.J., 2002, pp.854-857.M. Abramovici, M.A. Breuer, and A.D. Friedman, Digital Systems Testing and Testable Design, IEEE Press, Piscataway, N.J., 1990.P. Chandrakasan, S. Sheng, and R. W.Brodersen, Low Power CMOS Digital Design, IEEE J. Solid-State Circuits, vo1.27, no. 4, Apr. 1992, pp. 473-X84.J.L. Massey, G.H. Khachatrian, and M.K.Kuregian, Nomination of SAFER+ as Candidate Algorithm for the Advance Encryption Standard, Proc. 1 st AdvancedEncryption Standard Candidate Conf., 1998;/rblee/safer+.Bluetooth SIG, Specification of the Bluetooth system, Core, Part B;Baseband specification; Version 1 .1, 22 February 2001, at血 S.Sengodan,T.Luo,R.Bansal,H.Herlin; End-to-end Security Issues Wireless-IP Networks,”IASTED Applied Informatics,Austria,February in 15-17,2000 M.Bellare,R.Canetti,H.Krawczykz, Keying Hash Functions for Message Authentication,Advances in Crypto 96 Proceedings ,Lecture Notes in Computer Sciences Vo1.1109,N.Koblitz ed.,Springer-Verlag,1996第 14 页 共 14 页蓝牙设备怎样工作在电气设备中存在很多种连接方式。 例如：许多台式计算机系统有一个CPU单位连接到鼠标、键盘、打印机等等。个人数字助理(PDA)通常将一根电缆和一个连接设备接在计算机上。 电视通常连接着录像机和一个线盒， 对三种成分实现细微的控制。无绳电话利用无线电波和其基座单元连接在一起，它有一个头戴式耳机用一根导线连接到电话上。在立体声系统中，CD唱机和其他的声音设备连接到接收器上，接收器连接到扬声器。当使用电脑、娱乐设备或者电话的时候，各种小的系统组成了整个电子器件。这些装置通过金属丝、电缆、无线电信号和红外线以及多种连接器、插头和协议相互通信。设备之间的连接现在正变得越来越复杂。有时候我们感觉为了在家里建立电气化我们似乎需要一个电机工程中的PhD.。在这篇文章中，我们将看到一种完全不同的连接方式蓝牙。蓝牙是一种无线的自动化装置，它有很多能使我们日常生活简化的有趣的特点。问题在于当两个设备之间要进行通信的时候，在通信开始之前，它们不得不相互统一很多的因素。第一点是物理的协议：它们是用线缆还是无线信号？如果他们用电缆，需要多长呢？1m，2m，8m还是25m？一旦物理特征被决定了，又会出现一些新的问题：信号在串行通信口中一次能传输1bit，在并行通信口中能传输多位（通常是8或者16bit一次）台式计算机采用串行和并行两重方式与其他外围设备通信，如：调制解调器、鼠标和键盘安装串行的方式通信，而打印机用并行数据传输。所有的电子方面的讨论均围绕的是bit是什么意思，接受的消息是否和发出的数据是一样的。这需要命令语言和一个已作为协议的回应。现在多数产品已经有了一个标准的协议，事实上现在大多数公司都这么做以使一种产品能和其他的产品相互通信。调制解调器就属于这个范畴。其他设备用他们自己的方式通信，这就意味着一种产品收到的其他的产品的消息可能会出现乱码。打印机就是这样，它有特别的标准，像打印机控制语言和PostScript。电脑制造商、娱乐设备系统和其他的电子设备生产商就意识到错综复杂的电缆和连接器会使得即使是专业的技术员在第一次试的时候也很难建立正确的系统连接。当人们买了各种部件准备学着和回忆着要在家里把电脑和娱乐设备装起来的时候是极其可怕的。为了使家庭电器使用起来跟人性化，我们需要更好的方式把这些电子设备方便的连接在一起。这就是为什么出现了蓝牙设备的原因。蓝牙基础蓝牙是有一群同意任何电器装备如：电脑、移动电话、键盘、耳机等的电子设备生产商产生的一个标准协议，它有自己的连接方式，没有金属丝，没有电缆，用户也没有任何直接的行为来控制。蓝牙是一个确定的工作在两个层面的标准：它提供一个物理层的标准蓝牙是一种无线射频标准。它也在物理层之上的层面提供协议，在这里数据要被发送的时候，产品必须确定一次应该发送多少数据，在一次连接中怎么能确定从属设备收到的消息就是发送设备发出的消息。蓝牙特别小组的超过1000个的成员公司想在电话，电脑和外围设备之间让蓝牙无线通信代替各式各样的电缆。其他的无线连接方式：现在有多种无线连接方式。一种是用红外线谱来携带消息，红外线要求一种肉眼看不见也说不明白的低频光波。红外线大多用在电视系统的遥控系统中，存在一个红外线数据协会（IrDA），过去大多数用在电脑和外围设备的连接中。在这些电脑和娱乐设备使用红外线的目的和方式中，多数是使用一种数字模式信号的发射和关闭以及数从一点传送到另一点是非常快速的。红外线通信是非常值得信赖的，而且在一个设备中装上红外设备价格不高，但红外线也有其不足的地方：一、红外线是一种“视线”技术，如：你不得不把遥控器对准电视机或者DVD来使它正常工作。二、红外线是一种“点对点”的技术，你可以在台式机和笔记本电脑上传输数据，但不能同时在笔记本和掌上设备上利用红外线 传输数据。红外线的这两个特性有时候也是它的优点所在，因为红外线的发射和接收装置要被连接在一条线上，所以在他们之间很少出现干扰信号。点对点的特性也使得消息只能发送到特定的接收者，即使是在满是红外线探测器的房间也可以做到这一点。蓝牙解决方案蓝牙技术有意解决红外线和电缆同步系统的问题。硬件生产商，包括西门子、英特尔、东芝、摩托罗拉和爱立信发明了一种非常小的射频模块来装在电脑、电话机和娱乐电子设备中，从用户的角度来说，蓝牙设备有三个重要的特点：它是无线的，当走动的时候，你不需要担心公文包里会出现好多电缆连接你的各种设备，你可以随心设计你的办公室而不必为各种线应该从那里穿过而烦心。它的廉价性，这个问题你根本不必考虑。蓝牙不需要你做什么特别的事情来使它工作。设备会找到其他设备并建立其连接，而用户不需要输入任何东西。蓝牙的工作频率，蓝牙通信的工作频率在2.45GHz，这个频段被国际社会专门留出来供工业、科学和医疗器械使用（ISM）。你所使用的大多数设备可能已经利用上这个射频带了，婴儿监听器、车库门的开启器以及新一代的无绳电话都在利用这个ISM频带。可以肯定的是蓝牙及这些设备在设计的工程中不会出现与现有的设备形成很大的相互干扰的情况。避免干扰：低能量 蓝牙设备为了避免干扰情况的一种方式就是发出功率只有1毫瓦的信号。经比较，最消耗能量的蜂窝电话能发射3瓦的信号。低能量限制了蓝牙的传输范围大概只有10m，这样就切断了个人电脑与便携电话或者电视机之间的相互干扰。即使这样低的能耗。你的房间的墙壁也不能阻止蓝牙信号，这样的标准有利于控制在不同房间的多个设备。 这么多的蓝牙设备存在于你的房间，你可能会想它们之间会存在相互干扰，但这是不可能的。在下面的文字中，我们来看看这是为什么？避免干扰：跳频 几种设备在同一时间使用同一频率是不可能出现的，因为蓝牙使用一种技术一一跳频。在这一技术中，一个设备将在指定的范围内用到79个独立的、为经安排选择出来的频道，在有规律的基础上从一个频率变到另一个频率。在蓝牙技术中，信号发生者每秒改变频率1600次，这意味着更多的设备能充分地利用一个有限的无线射频光谱段。正因为发生器能自动的使用跳频技术，所以在同一时间两个发生器会使用相同的频率的情况不可能出现。这种技术
- 温馨提示:
1: 本站所有资源如无特殊说明，都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
2: 本站的文档不包含任何第三方提供的附件图纸等，如果需要附件，请联系上传者。文件的所有权益归上传用户所有。
3.本站RAR压缩包中若带图纸，网页内容里面会有图纸预览，若没有图纸预览就没有图纸。
4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
5. 人人文库网仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对用户上传分享的文档内容本身不做任何修改或编辑，并不能对任何下载内容负责。
6. 下载文件中如有侵权或不适当内容，请与我们联系，我们立即纠正。
7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
人人文库网所有资源均是用户自行上传分享，仅供网友学习交流，未经上传用户书面授权，请勿作他用。
川公网安备: 51019002004831号