问题 问答题 简答题

公钥密码体制与对称密码体制相比有什么优点和不足?

答案

参考答案:优点:

(1)密钥的分发相对容易;

(2)密钥管理简单;

(3)可以有效地实现数字签名。

缺点:

(1)与对称密码体制相比,费对称密码体制加解密速度比较慢;

(2)同等安全强度下,费对称密码体制要求的密钥位数要多一些;

(3)密文的长度往往大于明文长度。

填空题

Part 4


Questions 26-45


·Read the following passage and decide which answer best fits each space.
·Forquestions26-45, markoneletterA, B, C or D on the Answer Sheet.
Both (26) and zoology are parts of a more general field of science, biology. The two are studies of (27) things, which share certain characteristics, (28) they are plants or animals. Botany deals with plants, whose organisms that can (29) their own food by the use of sunlight. Zoology on (30) hand, deals with animals, those organisms that cannot manufacture their own food and are thus dependent (31) plants for their food.
(32) plants and animals share many abilities, the extent (33) which plants can exercise some of those abilities is (34) . For example, both plants and animals need food, water, and warmth for growth, (35) plants can move to (36) those needs only by the slow extraction of their leaves and roots, while animals can move relatively (37) distances in relatively little time. When an animal is hurt with needle, the animal will (38) the part of the body (39) . This ability to draw back (40) pain or irritation, called irritability, is found only to a very limited extent in plants.
If plants (41) the same (42) as animals, animals would have had a more difficult time finding food. If animals were as limited as plants, they might (43) a means of manufacturing their own food, as plants do now. The world would be a very different place (44) it is if the characteristics of plants and animals were (45)

A.share

B.achieve

C.extend

D.withdraw

单项选择题