问题 单项选择题

在公用密钥数字签名技术中,使用单向散列函数生成信息摘要的目的是______。

A.防止交易者抵赖

B.防止信息被篡改或伪造

C.为了便于解密明文

D.给接收方传递密钥

答案

参考答案:B

解析: 数字签名使用的技术决定了数字签名的功能x安全单向散列函数的特性使得不同数据生成相同加密摘要的可能性很小,从而保证了数据传输过程中的完整性;公开密钥加密技术决定了除发送者之外,其他任何人都不可能产生该密文,从而证明了发送者的身份,也使得发送者无法抵赖。

阅读理解

阅读理解。

     In many countries the standard of living enjoyed by their people has increased rapidly in recent years.

Sadly, not everyone in these countries is so fortunate and many people in rich countries are homeless.

     The reasons for homelessness are various, but poverty (贫穷) is undoubtedly one of the main causes.

The homeless people may have become jobless and then been unable to pay their rent and so no longer

have a roof over their heads. Often, the fact that unemployed people get help from the government prevents

this from happening, but not always.

     Some homeless people are mentally ill and have no one to look after them. Some are young people who,

for one reason or another, have left home and have nowhere to live. Many of them have had a serious

disagreement with their parents and have left home, choosing to go to a city and live on the streets. Sometimes

they have taken such action because they have been unable to get on with a step-parent.

     Many homeless people get into the habit of begging to get enough money to stay alive, but many of the

general public refuse to give anything to beggars. Often they are moved on by the police, being accused (指

控), whether rightly or wrongly, of forceful begging. There are many who disrespect homeless people.

     Some cynics (愤世嫉俗的人) declare that homeless people choose to live the life which they lead. But

who would willingly choose to live in z shop doorway, under a bridge or in a cardboard box?

1. According to the text, what causes some people to be homeless?

A. Lack of money.

B. The increased standard of living.

C. No government help.

D. Agreement with their parents.

2. It can be inferred from the text that _____.

A. the homeless are willing to live under a bridge or in a cardboard box

B. you will not find homeless people in countries with a high standard of living

C. the mentally ill live on the stress because they want the company of other homeless people

D. the unemployed who receive help may still be among the homeless

3. In paragraph 2, "a roof over their needs" most probably means _____.

A. a cap

B. a car

C. a home

D. a covering

4. The author thinks that the homeless people are _____.

A. pitiful

B. troublesome

C. respectable

D. admirable

单项选择题