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A向B发送消息P，并使用公钥体制进行数字签名。设E表示公钥，D表示私钥，则 B要保留的证据是 (1) 。基于数论原理的RSA算法的安全性建立在 (2) 的基础上。 Kerberos是MIT为校园网设计的身份认证系统，该系统利用智能卡产生 (3) 密钥，可以防止窃听者捕获认证信息。为了防止会话劫持，Kerberos提供了 (4) 机制，另外报文中还加入了 (5) ，用于防止重发攻击(Replay Attack)。 2（）
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N-ISDN是在 (1) 基础上建立起来的网络，能够提供的最高速率是 (2) 。网络提供基本接口速率时，传输声音需要使用 (3) ，一路话音占用的数据传输率是 (4) ，占用户可用带宽的比例是 (5) 。 3（）
Packet-switching wireless networks are preferable (1) when transmissions are (2) bemuse of the way charges are (3) per packet. Circuit-switched networks are preferable for transferring large files or for other lengthy transmissions because customers are (4) for the (5) of time they use the network. 1（）
[A] Why is foreign text "rendered meaningless" when passed through an on-line translation tool According to Sabine Reul, who runs a Frankfurt-based translation company, translation tools have limited uses, and problems arise when web users expect too much from them. "A translation tool works for some things," says Reul, "Say a British company wants to order a box of screws from a German supplier. A sentence like ’We need one box of a certain type of screw’ is something that a machine could translate reasonably accurately--though primitively."[B] Yet when it comes to translating blocks of text—words and sentences that convey thoughts and sentiments, on-line tools are bound to fail, she adds. "Beyond simple sentences, the on-line process simply doesn’t work because machines don’t understand grammar and semantics, never mind idiom and style." "Language is not a system of signs in the mechanical sense of the word", says Reul, "It is a living medium that is used to convey thought. And that is where machines fail. Human input is indispensable as long as computers cannot think." Reul and other translators look forward to the day when clever computers might help to ease their workload--but that time has not arrived yet.[C] Earlier this month the small German town of Homberg-an-der-Efze, north of Frankfurt, had to pulp an entire print run of its English language tourism brochure after officials used an Internet translating tool to translate the German text. According to one report, the brochure was "rendered meaningless" by the on line tool. Martin Wagner, mayor of Homherg-an-der-Efze, admits that the town made a "blunder". As a result of officials trying to save money by getting the Internet to do a translator’s job, a total of 7,500 brochures had to be binned.[D] "It would be nice if computers could do the job. And certainly the quest for machine translation has prompted a lot of linguistic research that may prove valuable in unforeseen ways. But experience to date confirms that even the most subtle computer program doesn’t think and you need to be able to think in order to translate."[E] This story highlights some of the pitfalls of translating on line. There are many instant translation tools on the web, but they are best used for individual words and short phrases, rather than for brochures, books or anything complex. For example, one of the joys of the web is that it grants you access to an array of foreign news sources. Yet if you were to use a translation tool to try to make sense of such reports, you could end up with a rather skewed and surreal view of the world.[F] Until the dawn of thinking computers, on-line translation tools are best reserved for words, basic sentences and useful holiday phrase. For tourism brochures, newspaper reports and the rest, you will have to rely on some old fashioned "human input".[G] Relying on on-line translation tools can be a risky business, especially if you expect too much of it. For the time being, might translation be something best left to the humansOrder: 42
In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet. Spread spectrum simply means that data is sent in small pieces over a number of the (16) frequencies available for use at any time in the specified range. Devices using (17) spread spectrum(DSSS) communicate by (18) each byte of data into several parts and sending them concurrently on different (19) . DSSS uses a lot of the available (20) , about 22 megahertz(MHz).
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