06-4 6.4 Secure Networks and Policies.pptx

第1页：6.4 生词表

第2页：6.4 常用短语

第3页：主句为

Secure Networks and Policies Whatisa secure network?Can the Internet be made secure?[1]Although the concept of a secure network is appealing to most users,networks cannot be classified simply as secure or not secure because the term is not absolute—each group defines the level of access that is permitted or denied. Forexample,some organizations store data that is valuable. Such organizations define a secure network to be a system that prevents outsiders from accessing the organization's computers.分析：复合句。主句为networks cannot be classified simply as secure or not secure,beclassifiedas意思是“被分类为”。什么是安全网络?Internet是安全的吗?尽管安全网络的概念吸引着大多数用户，但我们不能把网络简单的分为安全的或不安全的，因为安全这个术语不是绝对的——每个团体规定允许访问或拒绝访问的标准。例如，一些机构存储着重要数据，这样的机构可能把安全网络定义为系统能够防止外界对本机构计算机的访问。

第4页：其他一些机构需要向外界提供有效的信息

Other organizations need to make information available to outsiders,but prohibit outsiders from changing the data. Such organizations may define a secure network as one that allows arbitrary access to data,but includes mechanisms that prevent unauthorized changes. Finally,many large organizations need a complex definition of security that allows access to selected data or services the organization chooses to make public,while preventing access or modification of sensitive data and services that are kept private.其他一些机构需要向外界提供有效的信息，但要禁止外界对数据的更改。这样的机构可能把安全网络定义为允许任意访问数据、但是要有能够防止非法更改数据的机制。最终，许多大型机构需要一个对安全的复杂定义，这种安全允许访问本机构对外公开的部分数据和服务，同时又禁止对其处于保密状态的敏感数据和服务进行访问或修改。

第5页：主句中的

[2]Because no absolute definition of information secure exists,the first stepan organization must take to achieve a secure system is to define the organization's security policy. The policy does not specify how to achieve protection. Instead,it states clearly and unambiguously the items that are to be protected.分析：复合句。主句中的an organization must take to achieve a secure system为定语从句，修饰主语thefirststep，to define the organization's security policy为动词不定式作表语。因为不存在信息安全的绝对定义，一个机构要获得安全系统的第一步就是定义机构的安全政策。政策不规定如何去实现保护，而是要清楚明白地表明哪些项目需要得到保护。

第6页：定义信息安全政策非常复杂

定义信息安全政策非常复杂。首要的复杂性在于信息安全政策与网络中的计算机系统的安全政策密不可分。尤其为横贯于网络中的数据定义安全政策并不能保证数据的安全。信息安全不能禁止在计算机上拥有账户的非法使用者获得数据的拷贝。Definingan information security policy is complex. The primary complexity arises because an information security policy cannot be separated from the security policy for computer systems attached to the network. In particular,defining a policy for data that traverses a network does not guarantee that data will be secure. Information security cannot prevent unauthorized users who have accounts on the computer from obtaining a copy of the data.

第7页：安全政策必须针对存储在磁盘上的数据

所以安全政策必须针对存储在磁盘上的数据、通过拨号调制解调器用电话线传送的数据、书面形式打印出来的信息、通过便携的媒介如软盘传送的数据以及通过计算机网络传送的数据等。The policy must hold for the data stored on disk,data communicated over a telephone line with adialupmodem,information printed on paper,data transported on portable media such asafloppydisk,and data communicated over a computer network.

第8页：定义安全政策也

定义安全政策也是复杂的，因为每个机构必须决定哪些方面的保护是最重要的，而且常常要在安全和易于使用之间进行折衷处理。例如，某个机构可以考虑以下几个方面：数据完整性；数据可用性；数据机密性和保密；可说明性。Defining a security policy is also complicated because each organization must decide which aspects of protection are most important,and often must compromise between security and ease of use. Forexample,an organization can consider:DataIntegrity；DataAvailability；Data Confidentiality and Privacy;Accountability.

第9页：习题6.4 一 判断正误

习题6.4 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. ( ) Networks can be classified as secure or not secure.
2. ( ) Security policy specifies how to achieve protection.
3. ( ) Defining a policy for data that traverses a network does not guarantee that data will be secure.
4. ( ) A security policy cannot be defined unless an organization understands the value of its information.
5. ( ) Many large organizations need a complex definition of security that allows access to selected data or services the organization chooses to make public.
6. ( ) An absolute definition of information secure exists.
7. ( ) Information security must prevent unauthorized users who have accounts on the computer from obtaining a copy of the data.
8. ( ) Each group defines the level of access that is permitted or denied.

第10页：习题6.4 二 填空

习题6.4 二 填空：根据课文内容在横线处填入恰当的词。

Fill in the blanks according to the passage.

1. _________________ refers to protection from change: is the data that arrives at a receiver exactly the same as the data that was sent?
2. _________________ refers to protection against disruption of service: does data remain accessible for legitimate uses?
3. ______________________ refer to protection against snooping or wiretapping: is data protected against unauthorized access?
4. ________________ refers to how an audit trail is kept: which group is responsible for each item of data? How does the group keep records of access and change?
5. Networks cannot be __________simply as secure or not secure because the term is not absolute—each group defines the level of access that is permitted or denied.
6. The concept of a secure network is ____________to most users.
7. Such organizations define a secure network to be a system that prevents outsiders from ___________ the organization’s computers.
8. Many large organizations need a complex __________ of security.

第11页：习题6.4 三 翻译

习题6.4 三 翻译：将下列单词和短语译成中文。

Translate the following words into Chinese.

1. appeal to
2. data integrity
3. data availability
4. data confidentiality
5. integrity mechanisms
6. prohibit…from
7. be responsible for
8. be analogous to
9. result from
10. information security