06-3 6.3 Internet Security.pptx

第1页：6.3 生词表

第2页：6.3 生词表（续）

第3页：6.3 常用短语

第4页：6.3 互联网安全 课文要点

语言点分析：这是“the+形容词比较级，the +形容词比较级”句型，表示“越……越……”。网络安全近几年来，Internet使人们的生活改变了许多。人们使用e-mail，通过IP电话和朋友交谈，从网上获取最新信息，在网络市场购物。与传统通信渠道相比，Internet有许多优势：成本低效率高、信息传送速度快、并且不受时间和地点的限制。使用Internet的人越多，对Internet安全的关注就越多。6.3 Internet Security In recent years,Internet changes our life alot. Weusee-mail and Internet phone to talk with our friends,we get up-to-date information through web and we do shopping in the cyber-market. Internet has many advantages over traditional communication channels,e. g. it's costeffective,it delivers information fast and it is not restricted by time and place.[1]The more people use Internet,the more concerns about Internet security.

第5页：在人与人之间直接交流的社会

在人与人之间直接交流的社会，安全取决于物理线索。略举几例：人们用签名来表明自己的身份；人们把信函密封起来，防止他人窥视和更改；人们接受商店里有公章的收条来证明已经付款；人们从可靠的地方获取信息。不过对Internet安全而言，就没有这样的物理提示。对Internet通信，人们关心两个方面，第一是保密——如何确信数据在传输过程中没有人阅读过？第二是认证——如何确信某个人（或计算机）所声称的身份。In person-to-person community,security is based on physical cues. Tonamebuta few,we use our signature to authenticate ourselves;we seal letters to prevent others inspection and modification;we receive receipt with the shop'schop to make sure we paid;we get information from a reliable source. But in the Internet society,no such physical cueis available. Therearetwo areas that we show concern about in Internet communication. The first one is secrecy—how do we ensure no one reads the data during its transmission?The second one is authentication how can we be sure that the identity of someone claiming"whoitis".

第6页：解决数据安全问题的途径

解决数据安全问题的途径是加密。在现实生活中，如果汤姆想和玛丽密谈，他可以找一间没人的房子和玛丽安静地交谈，或者他用只有他们两人明白的密码交谈。在Internet，人们用第二种方法——加密——来传输数据。加密技术有两种——对称密钥加密和非对称密钥加密。Encryption is the way to solve the data security problem. Inreallife,if Tomwantsto talk with Marysecretly,he can choose a room with nobody there and talk with Maryquietly,or he can talk with Maryusing codes understandable by Tomand Maryonly. We take the second approach—encryption—to transmit data through Internet. Therearetwo kinds of encryption techniques—symmetric key encryption and asymmetric key encryption.

第7页：对对称密钥加密来说

For symmetric key encryption,both parties should have a consensus about a secret encryption key. When Awantstosend a message to B,Ausesthe secret key to encrypt the message. After receiving the encrypted message,Busesthesame(orderived)secret key to decrypt the message. The advantage of using symmetric key encryption lies in its fast encryption and decryption processes(when compared with asymmetric key encryption at the same security level).对对称密钥加密来说，当事人双方要有一致的密钥。当A要给B发送消息时，A用密钥将消息加密。B收到加密的消息后，用相同的（或最初的）密钥将消息解密。对称密钥加密的优点在于它的加密和解密速度快（与相同安全标准下的非对称密钥加密术相比）。

第8页：它的缺点是

它的缺点是：第一，在发送秘密消息之前，当事双方必须安全地交换密钥；第二，对不同当事人，人们必须使用不同的密钥。例如，如果A和B、C、D及E通信，A必须用四种不同的密钥。否则，B将知道A和C以及A和D在谈论什么。要找到安全交换密钥的方式很困难，所以，对称密钥加密的缺点使它不适合用于Internet。The disadvantages are,first,the encryption key must be exchanged between two parties in a secure way before sending secret messages. Secondly,we must use different keys with different parties. Forexample,if A communicates with B,C,DandE,Ashoulduse 4 different keys. Otherwise,Bwillknow what Aand Caswellas Aand Dhavebeen talking about. The drawbacks of symmetric key encryption make it unsuitable to be used in the Internet,because it's difficult to find a secure way to exchange the encryption key.

第9页：对非对称密钥加密

For asymmetric key encryption,there isapairofkeys for each party:a public key and a private key. Thepublickey is freely available to the public,but only the key owner gets hold of the private key. Messages encrypted by a public key can only be decrypted by its corresponding private key,and viceversa. When Asendsa message to B,Afirstgets B'spublickey to encrypt the message and sends it to B. After receiving the message,Buseshis private key to decrypt the message.对非对称密钥加密，当事各方都有一对密钥：公钥和私人密钥。公钥可自由使用，但只有密钥持有者拥有私人密钥。用公钥加密的消息只能用相应的私人密钥解密，反之亦然。当A给B发送消息时，A首先得到B的公钥将消息加密，然后发送给B。B收到消息后，用他的私人密钥将消息解密。

第10页：这种加密术的优点

The advantage comes in the public key freely available to the public,hence free from any key exchange problem. The disadvantage is the slow encryption and decryption process. Asymmetric key cryptography seems to attain secrecy in data transmission,but the authentication problem still exists. Consider the following scenario:when Asendsa message to B,Agets B'spublickey from the Internet—but how can A know the public key obtained actually belongs to B?Digital certificate emerges to solve this problem.这种加密术的优点是人们可以自由获得公钥，因此从交换密钥问题中解脱出来。它的缺点是加密和解密速度慢。非对称密钥加密在数据传输上似乎是安全的，但依然存在认证问题。请考虑如下情节：当A给B发送消息时，A从互联网上得到B的公钥——A怎样才能知道他获得的公钥确实属于B？这个问题由数字证书来解决。

第11页：是可信任的第三方

Digital certificate is an identity card counterpart in the computer society. Whenaperson wants to get a digital certificate,he generates his ownkeypair,gives the public key as well as some proof of his identification to the Certificate Authority(CA).CAwillcheck the person's identification to assure the identity of the applicant.[2]If the applicant is really the one"whoclaimstobe",CAwillissuea digital certificate,with the applicant's name,e-mail address and the applicant's public key,which is also signed digitally with the CA'sprivate key. CA指“证书授权机构”，是可信任的第三方，它保证数字证书的有效性。CA负责注册、颁发证书，并在证书包含的信息变得无效后收回证书。数字证书相当于电脑世界的身份证。当一个人想获得数字证书时，他生成自己的一对密钥，把公钥和其他的鉴定证据送达证书授权机构，证书授权机构将核实这个人的证明，来确定申请人的身份。如果申请人确如自己所声称的，证书授权机构将授予带有申请人姓名、电子邮件地址和申请人公钥的数字证书，并且该数字证书由证书授权机构用其私有密钥进行数字签名。

第12页：当A要给B发送消息时

当A要给B发送消息时，A必须得到B的数字证书，而非B的公钥。A首先核实带有证书授权机构公钥的签名，以确定是否为可信赖的证书。然后，A从证书上获得B的公钥，并利用公钥将消息加密后送给B。When Awantstosend Bamessage,instead of getting B'spublickey,Anowhastoget B'sdigital certificate. Afirstchecks the certificate authority's signature with the CA's public key to make sure it's a trustworthy certificate. Then Aobtain B'spublickey from the certificate,and uses it to encrypt the message and sends it to B.

第13页：认证是日常生活中的重要部分

Authentication is an important part of everyday life. Thelackof strong authentication has inhibited the development of electronic commerce. Itisstill necessary for contracts,legal documents and official letters to be produced on paper. Strong authentication is then,a key requirement if the Internet is to be used for electronic commerce. Strong authentication is generally based on modern equivalents of the one time pad. Forexample,tokens are used in place of one-time pads and a restored on smartcards or disks.认证是日常生活中的重要部分。缺少强有力的认证制约了电子商务的发展。写在纸上的合同、法律文件和官方信函仍是必要的。如果互联网用于电子商务，强有力的认证是一个关键要求。强有力的认证通常是建立在现代版的一次性密码本技术上的。例如，令牌用来代替昔日的一次性密码本，而且储存在智能卡或磁盘上。

第14页：6.3 互联网安全 课文要点

语言点分析：lipservice意思是“说得好听的话，空口的应酬话”，when it gets in their way是状语从句，when前面和后面的it均指网络安全问题。许多人大肆空谈安全，但是当安全问题妨碍到他们时，又不想麻烦。建立一个无需用户时刻想起周围的安全保障系统的系统和网络是重要的。如果用户发现安全政策和系统过于约束，他们就会设法绕过安全政策和系统。安全是每个人的事情，只有通过人人协作、采用明智的政策并坚持实践，网络安全才能实现。[3]Many people pay great amounts of lipservice to security,but do not want to be bothered with it when it gets in their way. It's important to build systems and networks in such away that the user is not constantly reminded of the security system around him. Userswhofind security policies and systems too restrictive will find ways around them. Security is everybody's business,and only with everyone's cooperation,an intelligent policy,and consistent practices,will it be achievable.

第15页：习题6.3 一 判断正误

习题6.3 一 判断正误：根据课文内容判断下列说法正误。

Put“true”or“false”in the brackets for the following statements according to the passage.

1. ()In this article,“cyber market”means a market that sells all kinds of goods.
2. ()In Internet communication, we show concern about secrecy and authentication.
3. ()Thetwokinds of encryption techniques used in the Internet are symmetric key encryption and asymmetric key encryption.
4. ()Checking the person’s identification is one of the CA’stasks.
5. ()Internet delivers information fast and it is not restricted by time and place.
6. ()In person-to-person community, security is based on physical cues.
7. ()Encryption is the only way to solve the data security problem.
8. ()The advantage of using symmetric key encryption lies in its fast encryption and decryption processes.

第16页：习题6.3 二 练习

习题6.3 二 练习：根据课文内容完成下列练习。

Fillinthe blanks according to the passage.

1. _____________people use Internet,____________concerns about Internet security.
2. Many people pay great amounts of____________to security, but do not want to be bothered with it when it gets in their way.
3. Whenaperson wants to get a digital certificate, he generates his ownkeypair, gives the____________as well as some proof of his identification to the Certificate Authority.
4. Therearetwo kinds of encryption techniques—________key encryption and___________key encryption.
5. Digital certificate is an identity card______________in the computer society.
6. Thelackof strong authentication has________the development of electronic commerce.
7. Strong_______________is then, a key requirement if the Internet is to be used for electronic commerce.
8. Userswhofind security policies and systems too___________will find ways around them.

第17页：习题6.3 三 翻译

习题6.3 三 翻译：将下列单词和短语译成中文。

Translate the following words and expressions into Chinese.

1. up-to-date
2. symmetric key encryption
3. asymmetric key encryption
4. viceversa
5. as well as
6. identity card
7. digital certificate
8. Certificate Authority
9. a trustworthy certificate
10. one-time