RSA是一种基于(43)原理的公钥加密算法。网络上广泛使用的PGP协议采用 RSA和IDEA两种加密算法组成链式加密体系，这种方案的优点是(44)。POP还可以对电子邮件进行认证，认证机制是用MD5算法产生(45)位的报文摘要，发送方用自己的 RSA私钥对(46)进行加密，附加在邮件中进行传送。如果发送方要向一个陌生人发送保密信息，又没有对方的公钥，那么他可以(47)。

(78)

(79)

(76)

(77)

(71) is a one -way function that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string.

  (72) is a protocol that most USENET machines now use it to allow news articles to propagate from one machine to another over a reliable connection.

  (73) is an approach preferred by cable TV providers. In this solution the fiber terminates at an optoelectrical converter and the final segment is a shared coaxial cable.

  (74) is a device used to connect two separate network that use different communication protocol.

  (75) is a digital-to-digital polar encoding method in which the signal level is always either positive or negative.

(73)

(74)

(71)

(72)

In the following essay, each blank has four choices. Choose the most suitable one from the four choices and write down in the answer sheet.

 Open Shortest Path First(OSPF) is a(66)routing algorithm that(67)work done on the OSI IS-IS intradomain routing protocol. This routing, as compared to distance-vector routing, requires(68)processing power. The Dijkstra algorithm is used to calculate(69)OSPF routing table updates only take place when necessary,(70)at regular intervals.