问题 单项选择题

分组密码是对明文分为同样大小的数据组分别加密,则下面说法正确的是( )。

A.在给定原始密钥之后,在加密过程中密钥自动转换

B.分组密码的数据可以调换位置而序列密码不行

C.分组密码是对明文序列进行转换或置换等操作

D.序列密码是对明文序列进行异或操作

答案

参考答案:D

解析:[分析] 序列密码的加密过程是把报文、话音、图像、数据等原始信息转换成明文数据序列,然后将它同密钥序列进行逐位模2加(即异或运算),生成密文序列发送给接收者。接收者用相同密钥序列进行逐位解密来恢复明文序列。所以选项D正确。

填空题
阅读理解

阅读理解。

      Class 5A was the worst class in Hill Valley High School. The students were badly behaved and had no

interest in their lessons.

      When a new principal (校长) came to work at the school, he decided to do something about Class 5A.

      On the second day of school he left his office and walked to 5A's classroom. He didn't need to know

where it was. He could hear them. They were making a terrible noise.

      He stood outside the classroom for a few moments and looked inside through the window. He was

disgusted (感到厌恶的) by what he saw.

      Some boys were fighting. Others were throwing things at one another. No one was doing any work.

      The principal had experienced badly behaved classes before. He knew what to do. He would go into

the classroom, take hold of the biggest boy in the class and punish him. This would be an example to the

others.

      He took a deep breath and opened the classroom door. The students paid no attention to him. 

      "Silence!" he shouted at the top of his voice.

      This time the students stopped what they were doing and looked at him. Quickly he walked up to the

oldest-looking boy in the room. He was also the noisiest boy in the room and had been shouting at the others

at the top of his voice.

      He took hold of him by the ear and pulled him to the front of the class.

      "I'm going to punish you as an example to the others," he said. "Now go to my office and wait for me."

      Then he turned to the class and gave them a lecture about how they should behave in school. 

      When he had finished what he said, "Does anyone have any questions?" 

      One of the students put up her hand, "Yes, sir. I have. When can we have our teacher back?"

1. The principal _____. [ ]

A. apologized to 5A for the noise

B. followed the sound to find 5A's classroom

C. was disgusting

D. had been at the school for several years

2. The principal was shocked at the scene in the classroom because _____.[ ]

A. the teacher was there

B. the boys were so big

C. the students were working quietly

D. it was too noisy

3. The principal decided to _____.[ ]

A. complain to the board of directors

B. punish everyone in the classroom

C. make an example of the boy who looked the oldest

D. pay attention to their complaints

4. What do you think the principal would feel after listening to what the girl said?[ ]

A. happy

B. sorry

C. excited

D. hopeful