问题 问答题 简答题

简述序列密码算法和分组密码算法的不同

答案

参考答案:

分组密码是把明文分成相对比较大的快,对于每一块使用相同的加密函数进行处理,因此,分组密码是无记忆的,相反,序列密码处理的明文长度可以小到1bit,而且序列密码是有记忆的,另外分组密码算法的实际关键在于加解密算法,使之尽可能复杂,而序列密码算法的实际关键在于密钥序列产生器,使之尽可能的不可预测性。

阅读理解

Going to a friend’s house is very exciting. You may spend time with a friend and get to see where he lives. So remember to be polite.

When to arrive?

The first thing to remember is that when a friend invites you over, you need to arrive on time. If your friend tells you to come around 3.00 p.m., that means you can turn up a little late after 3.00 p.m. But usually it is a good thing to arrive at the right time.

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Often it is also nice to bring something to your friend’s house. This could be a box of chocolates for you two to share, or maybe a movie that you can watch together. You can also bring some flowers. A little gift is a nice way to show your friend that you are excited to be at his house.

How to greet?

When you visit your friend’s house, you may also meet his parents. You should tell them who you are and they may tell you their names. As a child, I went to visit my friend Paul. I called his parents by their first names John and Mary. But now I know it is more polite to call them Mr or Mrs Smith. This will show them more respect (尊重) and then they may tell you to call them by their first names. Another way to show respect is to call them Madam or Sir.

It is a cool thing to visit a friend’s house. Be polite to your friend and your friend’s parents, and they will invite you again.

小题1:If your friend asks you to get to his house around 4.30 p.m., it is polite to arrive at ______.

A.4.00 p.m.

B.4.35 p.m.

C.5.30 p.m.

D.6.00 p.m.小题2: Which of the following can we choose for the blank (空白) in the passage?

A.What to watch

B.What to eat

C.What to bring

D.What to wear小题3: The passage mainly tells us _______.

A.when to arrive at your friend’s house

B.how to greet your friend’s parents

C.what to bring to your friend

D.how to be a good visitor小题4:The passage may be from _______.

A.an article in a magazine

B.a letter from a child to parents

C.a TV advertisement

D.a TV news report

选择题