网络与信息安全技术论文范文英文版

信息技术与网络安全论文范文英文版

计算机犯罪的类型划分 1、计算机犯罪的类型，由于着眼点的不同，有不同的分类，视计算机在犯罪中的角色而定。有学者认为，计算机在犯罪中所扮演的角色主要有：（1）计算机作为犯罪的目标（OBJECT），盗取硬件或软件数据等（2）计算机作为犯罪的主体（SUBJECT）或环境（ENVIORONMENT），如电子转帐欺诈等（3）计算机作为犯罪的工具，如计算机间谍刺探机密等（4）计算机作为犯罪的象征或符号（SYMBOLS），即计算机可能被用来作为掩饰计算机或滥用行为。 2、美国刑法学界的计算机犯罪分类-1。（1）计算机滥用（Computer Abuse）凡故意或过失以使用计算机的方法致使他人受损失或有损失危险的，即为计算机滥用行为的主体为计算机的所有人或操作者（Perpetrator 犯罪者）以计算机作为直接且显著的工具（2）与计算机相关的犯罪（Computer Related Crime）任何借助计算机知识以达到犯罪目的的犯罪行为在主观和客观上均与计算机有关许多属于传统犯罪类型、但因为有计算机介入的犯罪大多数属于此类（3）计算机犯罪（Computer Crime），范围比与计算机相关犯罪狭隘以欺诈或夺取的目的而执行程序以陷他人于错误或欺诈的目的而获金钱、财产或服务任何人恶意接近、改变、增减、损坏计算机系统、计算机网络或资料的，均为计算机犯罪计算机欺诈（Computer Fraud），很多与银行有关计算机辅助犯罪（Computer Assisted Crime），以计算机为犯罪手段或工具3、美国刑法学界的计算机犯罪分类-2。（1）刑事犯罪。破坏、毁损计算机系统（2）财产犯罪。通过计算机窃取财产（3）数据犯罪。盗取计算机数据（4）经济犯罪。凭借计算机实施复杂的财产欺诈案件4、德国法学界的计算机犯罪分类-1（1）利用计算机操作对数据处理系统的欺诈（2）盗窃计算机硬件与软件（3）计算机破坏（4）窃取劳务（5）凭借数据处理的帮助违反传统的计算机犯罪5、德国法学界的计算机犯罪分类-2（1）数据输入、处理的不正当操作（2）有关数据处理的计算机间谍（3）数据处理的破坏（4）盗窃使用（5）侵入数据处理系统6、日本法学界的计算机犯罪分类-1（1）将计算机用于不良目的的行为（2）危害计算机的行为（3）窃取计算机存储数据的行为7、日本法学界的计算机犯罪分类-2（1）破坏计算机的行为（2）盗窃计算机数据（3）盗窃计算机设备（4）欺诈及侵占（5）机器时间的窃用（6）对隐私权的侵害8、中国台湾法学界的分类（1）计算机操纵类犯罪（Computer Manipulation Crime）输入操纵（Input Manipulation）程序操纵（Program Manipulation）输出操纵（Output Manipulation）（2）计算机间谍类犯罪（Computer Espionage Crime）（3）计算机破坏类犯罪（Computer Sabotage Crime）（4）计算机窃用类犯罪（Occupy Computer Time）9、联合国文件中的计算机犯罪分类（1）利用计算机的欺诈行为（2）利用计算机伪造（3）损毁或修改计算机程序（4）非法进入他人计算机系统及服务（5）非法复制受保护的计算机系统软件10、欧洲理事会《关于网络犯罪的公约》（2001年11月）中的计算机犯罪分类（1）侵犯计算机数据或系统的机密性、完整性及可用性的犯罪非法访问非法截获数据干扰系统干扰设备滥用（2）与计算机有关的犯罪未经授权故意输入、修改、删除、抑制计算机数据（3）与内容有关的犯罪儿童色情歧视（4）与侵犯版权有关的犯罪

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1 绪论随着互联网的飞速发展，网络安全逐渐成为一个潜在的巨大问题。网络安全性是一个涉及面很广泛的问题，其中也会涉及到是否构成犯罪行为的问题。在其最简单的形式中，它主要关心的是确保无关人员不能读取，更不能修改传送给其他接收者的信息。此时，它关心的对象是那些无权使用，但却试图获得远程服务的人。安全性也处理合法消息被截获和重播的问题，以及发送者是否曾发送过该条消息的问题。大多数安全性问题的出现都是由于有恶意的人试图获得某种好处或损害某些人而故意引起的。可以看出保证网络安全不仅仅是使它没有编程错误。它包括要防范那些聪明的，通常也是狡猾的、专业的，并且在时间和金钱上是很充足、富有的人。同时，必须清楚地认识到，能够制止偶然实施破坏行为的敌人的方法对那些惯于作案的老手来说，收效甚微。网络安全性可以被粗略地分为4个相互交织的部分：保密、鉴别、反拒认以及完整性控制。保密是保护信息不被未授权者访问，这是人们提到的网络安全性时最常想到的内容。鉴别主要指在揭示敏感信息或进行事务处理之前先确认对方的身份。反拒认主要与签名有关。保密和完整性通过使用注册过的邮件和文件锁来实现。2 方案目标本方案主要从网络层次考虑，将网络系统设计成一个支持各级别用户或用户群的安全网络，该网在保证系统内部网络安全的同时，还实现与Internet或国内其它网络的安全互连。本方案在保证网络安全可以满足各种用户的需求，比如：可以满足个人的通话保密性，也可以满足企业客户的计算机系统的安全保障，数据库不被非法访问和破坏，系统不被病毒侵犯，同时也可以防止诸如反动淫秽等有害信息在网上传播等。需要明确的是，安全技术并不能杜绝所有的对网络的侵扰和破坏，它的作用仅在于最大限度地防范，以及在受到侵扰的破坏后将损失尽旦降低。具体地说，网络安全技术主要作用有以下几点：1．采用多层防卫手段，将受到侵扰和破坏的概率降到最低；2．提供迅速检测非法使用和非法初始进入点的手段，核查跟踪侵入者的活动；3．提供恢复被破坏的数据和系统的手段，尽量降低损失；4．提供查获侵入者的手段。网络安全技术是实现安全管理的基础，近年来，网络安全技术得到了迅猛发展，已经产生了十分丰富的理论和实际内容。3 安全需求通过对网络系统的风险分析及需要解决的安全问题，我们需要制定合理的安全策略及安全方案来确保网络系统的机密性、完整性、可用性、可控性与可审查性。即，可用性：授权实体有权访问数据机密性：信息不暴露给未授权实体或进程完整性：保证数据不被未授权修改可控性：控制授权范围内的信息流向及操作方式可审查性：对出现的安全问题提供依据与手段访问控制：需要由防火墙将内部网络与外部不可信任的网络隔离，对与外部网络交换数据的内部网络及其主机、所交换的数据进行严格的访问控制。同样，对内部网络，由于不同的应用业务以及不同的安全级别，也需要使用防火墙将不同的LAN或网段进行隔离，并实现相互的访问控制。数据加密：数据加密是在数据传输、存储过程中防止非法窃取、篡改信息的有效手段。安全审计：是识别与防止网络攻击行为、追查网络泄密行为的重要措施之一。具体包括两方面的内容，一是采用网络监控与入侵防范系统，识别网络各种违规操作与攻击行为，即时响应（如报警）并进行阻断；二是对信息内容的审计，可以防止内部机密或敏感信息的非法泄漏4 风险分析网络安全是网络正常运行的前提。网络安全不单是单点的安全，而是整个信息网的安全，需要从物理、网络、系统、应用和管理方面进行立体的防护。要知道如何防护，首先需要了解安全风险来自于何处。网络安全系统必须包括技术和管理两方面，涵盖物理层、系统层、网络层、应用层和管理层各个层面上的诸多风险类。无论哪个层面上的安全措施不到位，都会存在很大的安全隐患，都有可能造成网络的中断。根据国内网络系统的网络结构和应用情况，应当从网络安全、系统安全、应用安全及管理安全等方面进行全面地分析。风险分析是网络安全技术需要提供的一个重要功能。它要连续不断地对网络中的消息和事件进行检测，对系统受到侵扰和破坏的风险进行分析。风险分析必须包括网络中所有有关的成分。5 解决方案1 设计原则　　针对网络系统实际情况，解决网络的安全保密问题是当务之急，考虑技术难度及经费等因素，设计时应遵循如下思想：1．大幅度地提高系统

Disk storage medium such data recovery method research evidenceWith the popularization of computer and network， high-tech crime rampant， try to hide evidence of the Therefore， how to study the information on the storage medium access and analysis of computer forensics becomes an important This paper expounds the information technology based on data recovery module and traces found scanning for module， according to research and implementation of disk storage medium such circuit principle and data structure， analyses the causes and symptoms of data from software and hardware malfunction， two aspects elaborated fault data recovery methods and techniques， through the research and analysis of the file system under the Windows of network system and principles of existence and historical traces of storage device structure， using multiple data recovery software for various multiple data recovery， analyzes and studies the experiment of hard disk， mobile hard disk storage medium etc all kinds of information access ADAPTS to the recovery of tools， and the final design and realization of the data storage medium in depth and rapid scanning， the maximum found deleted after format data and the data， and the residue of the data already deleted the maximum recovery and Thus for judicial organs for electronic evidence， a new way to combat the computer crime will play a very important 给高分吧，180%正确，给分，谢拉

网络与信息安全技术论文范文英文版

可以直接google里面打中文自动翻译如果你连这3000千字都不想打你连这4年父母辛苦给你的学费都是糟蹋

With the development of computer technology and network technology， network security issues， today has become one of the most attention to the problem of the network world Many factors， which endanger the safety of the network， they mainly attached to the various malware， including viruses and trojans is most general Internet users are familiar According to these harmful factors， network security technology rapid development， it also greatly improved the security of the Aiming at network security situation now， on the company's network information security are analyzed and put forward the improvement Keywords: physical security， intrusion detection， firewall， switch， router

5000字的，网络安全相关的英文论文给

密码学在信息安全中的作用概述引言基于日常生活，同学们对密码的了解可能仅仅直观来自于社交账号的密码，银行卡的密码，若再提及电脑，可能就是开机密码。而严格的来说，上述所举密码都不是密码学中的密码，他们都只是一种口令。密码学是研究编制密码和破译密码的技术科学。研究密码变化的客观规律，应用于编制密码以保守通信秘密的，称为编码学；应用于破译密码以获取通信情报的，称为破译学，总称密码学。这里方便理解，我们可以举“门锁”的技术机制，因为它能在一定程度上反映密码学的技术思想。一、密码学的作用那么密码学的作用是什么呢？它是一门用来研究如何隐密地传递信息的学科。在现代特别指对信息以及其传输的数学性研究，常被认为是数学和计算机科学的分支，和信息论也密切相关。著名的密码学者Ron Rivest解释道：“密码学是关于如何在敌人存在的环境中通讯”。自工程学的角度，这相当于密码学与纯数学的异同。密码学是信息安全等相关议题，如认证、访问控制的核心。密码学的首要目的是隐藏信息的涵义，并不是隐藏信息的存在。由此可见，密码是通信双方按约定的法则进行信息特殊变换的一种重要保密手段，使得交流的信息获得安全保障不被他人获取。通俗一点来说，就是使信息伪装化，使未授权者不能得到信息的真实含义。二、密码学的一些相关概念首先不得不提的是加密密钥。因为加密解密都在它的控制下进行。其次是加密算法，它是用于加密的一簇数学变换，相应的，用于解密的一簇数学变换称为解密算法，而且解密算法是加密算法的逆运算，掌握了加密密钥和算法的人才算授权了的人。依照这些法则，变明文为密文（称为加密变换），变密文为明文（成为脱密变换），合法的通信双方就得以进行信息交流。三、密码的三个性质保密性，保真性和保完整性。所以密码学是在编码与破译的斗争实践中逐步发展起来的，并随着先进科学技术的应用，已成为一门综合性的尖端技术科学。它与语言学、数学、电子学、声学、信息论、计算机科学等有着广泛而密切的联系。它的现实研究成果，特别是各国政府现用的密码编制及破译手段都具有高度的机密性。四、密码的由来与信息安全的联系大约在公元前1900年前，古埃及一位奴隶主的墓志铭中就出现了一些古怪的符号。西方密码学家认为这是密码的最早出现。一般，墓志铭不需要保密，这样做大概是出于对墓主人的尊敬和追求文字表达的艺术性。而随着互联网的急速发展，网络信息的安全成了一项重大问题。密码在早期仅对文字或数码进行加、脱密变换，随着通信技术的发展，对语音、图像、数据等都可实施加、脱密变换，如今特别是在于电脑与网络安全所使用的技术，如访问控制与信息的机密性。所以密码学与计算机科学相互促进发展。现在密码学已被广泛应用在日常生活：包括自动柜员机的芯片卡、电脑使用者存取密码、电子商务等等。要说到密码与信息安全的关系，不难理解，密码是信息安全的关键技术或核心技术。从而，国际上，密码属于一个国家的主权。即，任何一个国家有自主选。再由于信息所需的保密性，几乎所有的信息安全领域都要应用密码技术，所以密码也是信息安全的共性技术。那么密码对信息安全的重要性也可见一斑了。五、信息安全的专业定义信息安全是指信息系统（包括硬件、软件、数据、人、物理环境及其基础设施）受到保护，不受偶然的或者恶意的原因而遭到破坏、更改、泄露，系统连续可靠正常地运行，信息服务不中断，最终实现业务连续性。信息安全主要包括以下五方面的内容，即需保证信息的保密性、真实性、完整性、未授权拷贝和所寄生系统的安全性。其根本目的就是使内部信息不受内部、外部、自然等因素的威胁。为保障信息安全，要求有信息源认证、访问控制，不能有非法软件驻留，不能有未授权的操作等行为。既然有人想要对信息进行加密处理，那么也有敌人想要破解密码从而截取信息。六、密码破译的发展与信息安全的联系1412年，波斯人卡勒卡尚迪所编的百科全书中载有破译简单代替密码的方法。到16世纪末期，欧洲一些国家设有专职的破译人员，以破译截获的密信。密码破译技术有了相当的发展。1863年普鲁士人卡西斯基所著《密码和破译技术》，以及1883年法国人克尔克霍夫所著《军事密码学》等著作，都对密码学的理论和方法做过一些论述和探讨。不得不说，两次世界大战对于密码学和信息安全来说都是发展的“绝胜时期”。第一次世界大战中的密码斗法。美国破译其他国家密码，一战结束后，军情处8 科被解散。雅德利带领留下的50多人成立了美国黑室”，专门破译各国的外交密电。1917-1929，雅德利领导的“美国黑室”小组破译了45000多份密电，包括中国、德国、英国、法国、俄国等20多国。10雅德利经营了十几年的 “美国黑室”被国务卿关闭，理由是“君子之间不偷看信件”。此语成为美国密码史上的一句名言。后来，雅德利把这段经历写成一本书《美国黑室》。第二次世界大战中的密码斗法。二战时期密码技术有了很大提高，一战时的密码技术主要依靠手工进行加解密，密码的复杂程度、安全性和加解密速度都不够高，密码破译人员主要由语言专家，猜谜专家，象棋冠军组成。战时的密码技术实现了机电化，加解密用机电装置进行，密码的复杂程度、安全性和加解密速度都有很大提高。密码破译人员也有数学专家的加入，并发挥主力作用。军事家评价：“盟军在密码方面的成功，使第二次世界大战提前十年结束”。中国的抗日战争是第二次世界大战的重要组成部分，值得骄傲的是中国人破译了日本部分密码，为赢得战争胜利作出了重要贡献为赢得战争胜利作出了重要贡献1938年底雅德利来重庆任军统密码破译顾问，为军统培训了200多名密码人才，7回国。后来我国破译了日本间谍的重庆气象密电，抓获了间谍；还破译了汪伪的一个间谍密码，并抓获了间谍；还破译了日本空军的密码，使重庆空战损失减小；还破译了日本外务省的部分密码，获得了珍珠港事件前的部分情报。到1949年美国人香农发表了《秘密体制的通信理论》一文，应用信息论的原理分析了密码学中的一些基本问题。自19世纪以来，由于电报特别是无线电报的广泛使用，为密码通信和第三者的截收都提供了极为有利的条件。通信保密和侦收破译形成了一条斗争十分激烈的隐蔽战线。当今世界各主要国家的政府都十分重视密码工作，有的设立庞大机构，拨出巨额经费，集中数以万计的专家和科技人员，投入大量高速的电子计算机和其他先进设备进行工作。与此同时，各民间企业和学术界也对密码日益重视，不少数学家、计算机学家和其他有关学科的专家也投身于密码学的研究行列，更加速了密码学的发展。最终密码学终于成为一门独立的学科。七、密码学与信息安全的联系密码学是一门跨学科科目，从很多领域衍生而来：它可以被看做是信息理论，却使用了大量的数学领域的工具，众所周知的如数论和有限数学。信息安全也是一门涉及计算机科学、网络技术、通信技术、密码技术、信息安全技术、应用数学、数论、信息论等多种学科的综合性学科。信息作为一种资源，它的普遍性、共享性、增值性、可处理性和多效用性，使其对于人类具有特别重要的意义。我国的改革开放带来了各方面信息量的急剧增加，并要求大容量、高效率地传输这些信息。传输信息的方式很多，有局域计算机网、互联网和分布式数据库，有蜂窝式无线、分组交换式无线、卫星电视会议、电子邮件及其它各种传输技术。信息在存储、处理和交换过程中，都存在泄密或被截收、窃听、窜改和伪造的可能性，所以安全的保障被高度重视起来。不管是机构还是个人，正把日益繁多的事情托付给计算机来完成，敏感信息正经过脆弱的通信线路在计算机系统之间传送，专用信息在计算机内存储或在计算机之间传送，电子银行业务使财务账目可通过通信线路查阅，执法部门从计算机中了解罪犯的前科，医生们用计算机管理病历，所有这一切，最重要的问题是不能在对非法（非授权）获取（访问）不加防范的条件下传输信息。由此我们提出安全策略这个术语，信息安全策略是指为保证提供一定级别的安全保护所必须遵守的规则。实现信息安全，不但靠先进的技术，而且也得靠严格的安全管理，法律约束和安全教育。八、密码学与信息安全共同迅速发展中国信息安全行业起步较晚，自本世纪初以来经历了三个重要发展阶段(萌芽、爆发和普及阶段，产业规模逐步扩张。带动了市场对信息安全产品和服务需求的持续增长;另外，政府重视和政策扶持也不断推动我国信息安全产业的快速发展。据《2013-2017年中国信息安全行业发展前景与投资战略规划分析报告》数据显示，2010年中国信息安全产品市场规模达到74亿元，同比增长23%。前瞻网认为，信息安全行业具有较大发展潜力，但目前国内互联网行业的信息安全形势不容乐观，随着网络日益渗透到社会生活的各个方面，增强网络信息安全意识、提升信息安全防范措施变得尤为迫切。2012年信息安全产业将步入高速发展阶段，而整个互联网用户对安全产品的要求也转入“主动性安全防御”。随着用户安全防范意识正在增强，主动性安全产品将更受关注，主动的安全防御将成为未来安全应用的主流。信息安全的市场主流电子商务将加密技术作为基本安全措施。加密技术分为两类，即对称加密和非对称加密。一、对称加密又称私钥加密，即信息的发送方和接收方用同一个密钥去加密和解密数据。它的最大优势是加/解密速度快，适合于对大数据量进行加密，但密钥管理困难。如果进行通信的双方能够确保专用密钥在密钥交换阶段未曾泄露，那么机密性和报文完整性就可以通过这种加密方法加密机密信息、随报文一起发送报文摘要或报文散列值来实现。二、非对称加密又称公钥加密，使用一对密钥来分别完成加密和解密操作，其中一个公开发布（即公钥），另一个由用户自己秘密保存（即私钥）。信息交换的过程是：甲方生成一对密钥并将其中的一把作为公钥向其他交易方公开，得到该公钥的乙方使用该密钥对信息进行加密后再发送给甲方，甲方再用自己保存的私钥对加密信息进行解密因为在互联网上，每台计算机都存在或多或少的安全问题。安全问题必然会导致严重后果。诸如系统被破坏，数据丢失，机密被盗和直接、间接的经济损失，这都是不容忽视的问题。既然说到安全，我们经常提到要使用防火墙、杀毒软件等等。而密码技术的有一个劣势就是密码不擅长解决信息处理形态的安全问题。这是目前病毒泛滥，而我们又没有很好办法的根本原因。因此请记住：“再好的密码也不能杀病毒，再好的杀病毒软件也不能当密码用”。两者都很重要！说了这么多，密码学与信息安全就是相辅相成的关系。密码学因信息安全得以更快发展，信息在密码学的保障下得以安全交流。参考文献：　　[1]谢希仁计算机网络(第4版)[M]北京:电子工业出版社，　　[2]张民，徐跃进网络安全实验教程，清华大学出版社，2007，　　[3]许治坤，王伟等网络渗透技术，电子工业出版社，2005-5-　　[4]武新华，翟长森等，黑客攻防秘技大曝光，清华大学出版社，2006．。。这是我之前纯手写的，还能关于密码学的，觉得能用就拿去吧

网络技术与信息安全论文范文英文版

需要的话我们团队也可以的原创按照要求定制包修改包过直到通过为止

论文不会写，最关键的是要把心态放正，一步步来，多看点范文，看看别人怎么写的，实在不会可以找别人代写，我以前也一样，最后找的NTA 。NTA这个站做的，质量还可以，顺利通过了，希望对你有帮助

信息技术网络安全论文范文英文版

Data Management1 why Data Management ? We have already considered hardware and software in some In this chapter， we turn our attention to a third basic computer resource， Many computer applications require that data be stored for subsequent [1] Simply storing the data is not enough， A typical computer system， even a small one， can have dozens of disks and tapes， each holding data for dozens of different For any given application， one and only one set of data will We must be able to store， Locate， and retrieve the specific data needed by a given That is the concern of data 2 Accessing DataImagine a single diskette containing several For a particular application， only one of those programs will How is a given program selected， loaded， and executed? In Chapter 6， we learned that the operating system， responding to a use’s command， reds the disk’s index， searches it for the requested program name， extracts the program’s track and sector address， and issues primitive commands to read it into main Later， following a RUN command， the program is given control of the Accessing data presents a similar A single diskette can hold data for several different For a given application， one and only one set of data will do， and finding the right data is much like finding the right There are differences between accessing programs and accessing data， When a program is need， all its instructions must be loaded into Data， on the other hand， are typically processed selectively， a few elements at Thus， it is not enough merely to locate the data; we must be able to distinguish the individual data elements， 1 Data Structures The key to retrieving data is remembering where they are stored， If the data elements are stored according to a consistent and well understood structure， it is possible to retrieve by remembering that The simplest data structure is a For example， data for a program that computes an average might be stored as a series of numbers separated by commas (F1) The commas distinguish the individual data Most programming languages support amore complex data structure called an array (Fig 2) Each array element can hold one data Each element is assigned a unique identifying number or numbers， and individual data elements can be inserted， extracted， or manipulated by referencing those For example， in the array pictured in F 2 elements are identified by a row number and a column number， and row 1， column3 (element1，3) contains the value Once an array has been filled， it can be written to disk， tape， or any other secondary medium， and back into memory for Consider a program that generates name and address For each label， we need a name， a street address， a city， a state， and a zip If we needed only a few labels， we might store the data in a list， but separating the elements would soon become An option is to set up an array of names and addresses， with each row holding the data for a single The only problem is that the entire array must be in main memory before the individual elements can be accessed， and main memory space is Thus， even with an array， we could generate relatively few F 1 The simplest data structure is a Separators， such as these commas， serve to distinguish individual Often， a “sentinel” value， such as a negative number， marks the end of the 4410， 843， 184， 31， 905， 6357， 44， 7702， 228， 59， -1 F 2 Most programming languages support a more complex data structure called an array Individual cells are assigned a number or numbers， and data values are inserted manipulated， and extracted by referencing those A better solution is to organize the data as a file (F3) All computer data begin as patterns of bits， On a file， the bits are grouped to form Groups of characters， in turn， form meaningful data elements called A group of related fields is a record the file is a set of related For example， in a name and address file， an individual’s name is a Each record holds a complete set of data for data for a single individual ( a name， a street address， and so on) he file consists of all the Fig 3 Characters are grouped to form Fields are prouped to form A file is a group of related The data in a file are processed record by Normally， the file is stored on a secondary medium such as Programs are written to read a process its fields， generate the appropriate output， and then read and process another Because only one record is in main memory at a time， very little memory is Because many records can be stored on a single disk， a great deal of data can be processed in this limited 2 Locating Files Imagine a file stored on The first step in accessing its data is finding the The task is much like finding a program， but there are Following a command such as LOAD or RUN， programs are loaded by the application Data， on the other hand， are processed by application programs， in the context of a program’s Typically， just before the data are required， the program asks the operating system to open the Each file has a name; the open logic ( 4 ) reads the index， searches it by name， and finds the address of the first record in the F4 when a file is opened， the disk index is read into main memory and searched for the desired file’s If the file name is found， the file’s start address is extracted from the 3 Locating Records Once a file has located， the process of accessing its records can When a program needs input data， it reads a record; when it is ready to output results， it writes a Note that these instructions deal with selected records， not with the entire We open We read and write Let’s examine the data accessing process more A programmer views data logically， requesting the next record， or the name and address for a particular The data are stored on a secondary medium such as To access a record physically， the disk drive must be give a set of primitive commands: seeks， reads， and The programmer thinks in terms of logical I/O The external device stores and retrieves physical sectors; it “thinks” in terms of physical I/O There must be a mechanism for translating the programmer’s logical requests to the appropriate physical commands (Fig 5) On small computers， much of the logic is found in the operating system’s input/output control system; on larger machines， access methods are Increasingly， the programmer’s logical data request is translated to physical form by a database management 4 The Relative Record Concept How does software， be it operating system， access method， or database software， find specific records in a file? [2] The key to many storage and retrieval techniques is the relative record Imagine a string of 100 Numbers indicate a given record’s position relative to the first record in the The file’s first record ( relative record 0 ) is at “ start of file plus 0 ”;Its second record is at “ start of file plus 1”， and so Access Methods Imagine preparing meeting announcements for a You need a set of mailing labels， and each member’s name and address is recorded on an index Probably the easiest way to generate the labels is to copy the data from the first card， turn to the second card and copy it， and so on， processing the records sequentially， form the beginning of the file to the Magazine publishers face the same problem with each new issue， but need mailing labels for tens of thousands of Rather than using index cards， they store customer data on disk or magnetic tape， one record per The easiest way to ensure that all labels are generated is to process the records in the order in which they are stored， proceeding sequentially from the fist record in the file to the To simplify handing， the records might be presorted by zip code or a mailing zone， but the basic idea of processing the data in physical order still How dos this relate to the relative record number concept? A relative record number indicates a record’s position on the With sequential access， processing begins with relative record 0， then moves to relative record 1， 2， and son Accessing data sequentially involves little more than For example， imagine a program has just finished processing relative record What is the next record? Obviously， relative record We’ve already seen how a relative record number can be converted to read them， or write them， in physical Processing records in sequence is not always For example， when a subscriber moves， his or her address must be changed in the fire searching for that subscriber’s record sequentially is like looking for a telephone number by starting with the first page of the telephone book and reading line and That’s no how we use a telephone Instead， knowing the record are stored in alphabetical order ，we quickly narrow our search to a portion of a single page and then begin reading the entries， ignoring the bulk of the data the way we use a telephone book is good example of direct， or random， A disk drive reads or writes one record at a To randomly access a specific record， all the programmer must do is remember its address， and ask for it the problem is remembering all those disk addresses， One solution is maintaining an index of the Again， we’ll use the name and address fire as an We want to access individual customer record by As the file is created， records are written one at a time， in relative record number Additionally， as each record is written， the customer name and the associated relative record number are recorded in an array or After the last record has been written to disk and its position recorded on the index， the index is itself Once the index has been created， it can be used to find individual Assume， for example， that Susan Smith has changed her To record her now address on the file， a program read the file index， search the index for her name， find her relative record number， compute the disk address， and read her record， change her address， rewrite the record to the same place on Note that this specific record is accessed directly， and that no other records in the file are The basic idea of direct access is assigning each record an easy to remember， logical， and then converting that key to a relative record number， Given this relative location， a physical address can be computed， and record Using an index is one technique for converting keys to physical An option is passing a numeric key to an algorithm and computing a relative record Both techniques have the same objective; converting a programmer’s logical data requests to physical Earlier in the chapter we identified the gap separating logical and physical I/O An access method is a software module that bridges this gap， converting logical keys to physical addresses， and issuing the appropriate primitive There are many variations of sequential， indexed， and direct organizations， and each one has its own access Using a variety of data access techniques can be confusing， and this is one reason for the growing popularity of database management systems4 Database Management There are problems with traditional data Many result from viewing applications For example， consider Most organizations prepare their payrolls by computer because using a machine instead of a small army of clerks saves Thus， the firm develops a payroll program to process a payroll file， Inventory， accounts receivable， accounts payable， and general ledger analysis are similar applications， so the firm develops an inventory program， and inventory file， an accounts receivable program， an accounts receivable file， and so Each program is independent， and each processes it own independent data Why is this a problem? For on thing， different application often need the same data For example， schools generate both bills and student grade View the applications The billing program reads a file of billing data， and the grade report program reads an independent file of grade The outputs of both program are mailed to each student’s home; thus， student names and addresses must be redundantly recorded on both What happens when a student moves? Unless both file are up data， one will be Redundant data are difficult to A more subtle problem is data Each access method has its own rules for storing and retrieving data， and certain “tricks of the trade” can significantly improve the efficiency of a given Bacause the motivation for using the computer is saving The programmer is often tempted to save even more by taking advantage of these Thus， the program’s logic becomes dependent upon the physical structure of the When a program’s logic is tied to its physical data structure， changing that structure will almost certainly require changing the As a result， programs using traditional access method can difficult to The solution to both problems is often organizing the data as a single， integrated The task of controlling access to all the data can then be concentrated in a centralized database management How dose the use of a centralized database solve the data redundancy problem? All data are collected and stored in a single place; consequently， there is one and only one of any given data When the value of an element ( an address， for example) changes， the single database copy is corrected， Any program requiring access to this data element gets the same value， because there is only on How dose a database help to solve the data dependency problem? Since the responsibility for accessing the physical data rests with the database management system， the programmer can ignore the physical data As a result， programs tend to be much less dependent upon their data， and generally much easier to Expect the trend toward database management to There are problems with traditional data Because different applications often require the same data， certain data elements may be stored in several different places， and such redundant data are difficult to Another problem is data If a program’s logic is too closely linked to the physical structure of its data， that program can be difficult to The solution to both problems is often collecting all the organization’s data in a centralized With a database， there is only one copy of each data element， so the data redundancy problem is Because every program must access data through a database management system， programs are insulated from the physical data structure; thus， data dependency is

网络与信息安全技术论文范文英文版高中

Since twentieth Century， the rapid development of computer technology， especially the rapid development of Internet technology， has put the whole world even as a whole， so that the social development is inseparable from the information It constantly changing economic， social， cultural structure and operation mode， and the transmission of information relating to financial， science education， military and other fields， in to the people and the country brings convenient， efficient information sharing at the same time， but also to the security of network information has brought many In today's international competitive situation， the network information security is more and more attention from all over the This article from the network information security problems and characteristics， the main techniques of network security， common network attack methods and countermeasures， the construction of network security and other aspects of the present stage of our country network information security problems and restricting factors and how from technology and management and other aspects the construction has the Chinese characteristic information security comprehensive security system， ensure our country network information 　　Key word　　The network information security of network attack network ethics network security comprehensive security system