如果网络中N个用户之间采用RSA算法进行加密通信，则整个加密通信系统共有 (49) 个密钥。
A．N×(N-1)
B．N
C．2N
D．NXN
参考答案：C
解析： 目前，主要的公钥算法包括RSA算法、DSA算法、PKCS算法与PGP算法等。非对称加密技术对信息的加密和解密使用不同的密钥，用来加密的密钥是可以公开的，用来解密的私钥是需要保密的。非对称加密技术可以大大简化密钥的管理，在网络中N个用户之间进行加密通信，仅仅需要使用N对密钥。换言之，加密通信系统共有2N个密钥。
In this section you will find after each of the passages a number of questions or unfinished statements about the passage, each with 4 (A, B, C and D) choices to complete the statement. You must choose the one which you think fits best. Blacken the corresponding letter as required on your Machine-scoring ANSWER SHEET. The time for this section is 70 minutes.
| Questions 51-55 are based on the following passage. To Err is Human by Lewis Thomas Everyone must have had at least one personal experience with a computer error by this time. Bank balances are suddenly reported to have jumped from $ 379 into the millions, appeals for charitable contributions are mailed over and over to people with crazy sounding names at your address, department stores send the wrong bills, utility companies write that they’re turning everything off, that sort of thing. If you manage to get in touch with someone and complain, you then get instantaneously typed, guilty letters from the same computer, saying, "Our computer was in error, and an adjustment is being made in your account." These are supposed to be the sheerest, blindest accidents. Mistakes are not believed to be the normal behavior of a good machine. If things go wrong, it must be a personal, human error, the result of fingering, tampering a button getting stuck, someone hitting the wrong key. The computer, at its normal best, is infallible. I wonder whether this can be true. After all, the whole point of computers is that they represent an extension of the human brain, vastly improved upon but nonetheless human, superhuman maybe. A good computer can think clearly and quickly enough to beat you at chess, and some of them have even been programmed to write obscure verse. They can do anything we can do, and more besides. It is not yet known whether a computer has its own consciousness, and it would be hard to find out about this. When you walk into one of those great halls now built for the huge machines, and standing listening, it is easy to imagine that the faint, distant noises are the sound of thinking, and the turning of the spools gives them the look of wild creatures rolling their eyes in the effort to concentrate, choking with information. But real thinking, and dreaming, are other matters. On the other hand, the evidence of something like an unconscious, equivalent to ours, are all around, in every mail. As extensions of the human brain, they have been constructed the same property of error, spontaneous, uncontrolled, and rich in possibilities. |
The title of the writing "To Err is Human" implies that ______.
A．making mistakes is confined only to human beings
B．every human being cannot avoid making mistakes
C．all human beings are always making mistakes
D．every human being is born to make bad mistakes