2. Are the statements true or false?

1. The mechanics of the authentication mechanism are under uniform physical control.

2. The objects being protected by the authentication mechanism are the computer systems.

3. The security of the computer system depends on the unforgeability of the user's identification.

4. Passwords as a general technique do not have any notorious defects.

5. One can easily guess the random sequence of letters.

6. Some systems have programs that generate invariable sequences of letters for use as passwords.

7. In systems where the terminal is distant from the computer, the password must be exposed to be used.

8. The computer system treats the code as a password that need not be kept secret.

9. The scheme is inconvenient, resists casual use, and provides a unconventional form of accountability through the physical objects used as keys.

10. The strategy of encipherment/decipherment is usually invoked for the purpose of providing communications security.

3. Answer the questions to the text.

1. How does authentication mechanism differ from the protection one?

2. What are the objects being protected by the authentication mechanism?

3. What are the possible elaborations and embellishments of this basic strategy?

4. What are the conventional techniques while choosing password?

5. What are the most significant defects of it?

6. What is the alternative approach to secrecy?

7. What are the weaknesses of such schemes?

8. What are the main features of the LUCIFER system?

9. Why can the strategy of encipherment/decipherment simultaneously be used for authentication?

GRAMMAR REVISION

1. Fill in the blanks with modal verbs.

A . "Granddad says he'll be glad when you get out of the house," the little girl said

after she had been sitting still for nearly a minute.

"Does he?" said Ted.

"Yes. He says he ... (not) trust you round the corner."

"Oh?"

"What ... you do round the corner?"

"I ... do a lot of things."

"What sort of things?"

"All sorts of things."

The girl occupied herself for a short time with her own thoughts. Then she said: "Mummy says you're a cheat. What is a cheat?"

"I don't know," said Ted rather bitterly.

"But ... you be a cheat if you don't know what it is?"

"I ... (not), of course. I am not one."

"Is Granddad a cheat?"

"I shouldn't be surprised."

"... I ask him if he is a cheat?"

"I don't think you ... ."

"Why not?"

"He ... (not) like it."

"Why not?"

"I don't know," said Ted. "I don't really know anything about cheats, Ann. And I think you ... have made a mistake about the word alto­gether."

B."The house is absolutely full of gas. Whatever have you been doing?" I asked the maid, entering her bedroom.

"I have done nothing," she said, weakly.

"Oh, then, who was it?" I said, trying to open the windows. "You ... have been dead. I ... (not) think what you ... have been doing. The gas oven was on. I suppose it ... have been Flora. Was she playing in the kitchen?" '

"Yes. She ... have done it. What a naughty girl, trying to kill us all."

"Do you mean," I said, "that you didn't even notice? That since seven o'clock you haven't noticed a thing?"

"I did not notice anything, no."

"You … be an idiot," I said. "What if I had stayed out all night, you'd probably all have been dead by the morning."

2. Supply the necessary modal verbs for the following sentences, noticing carefully the Russian equivalents given in brackets:

1. He ... not and ... not believe her. (не мог, не хотел) 2. Не sat, thinking unhappily of his talk with Jimmy. He wondered if he ... have stayed with him. He felt he ... have said something at least, to warn Jimmy against Smith. But what ... he have said? And Jimmy ... not have listened, (надо было бы, следовало бы, мог бы, не стал бы) 3. "By the way," I asked, "what's Bill doing now?" "How in the world ... I know?" Arthur looked pained. "I thought he ... have been bothering you for money." (откуда мне знать, может быть) 4. Не came out of the water, smiling. "You ... have come earlier," he said. "We ... have swum together. The water is great." (зря не пришел, могли бы) 5. "Last night, you know, Hugh suddenly began to speak to me about what my future was going to be like." "What ... it have meant?" "How ... I know?" (и что это могло значить, откуда мне знать) 6. There was an old apple tree beside the path. I said, "I bet I ... climb that." "No, you ... not," said Jack, (могу, не надо) 7. "Well, then, ... you hold the line while I find the letter?" "I ... not, I'm in a telephone box." "Then ... I ring you back?" "I'm not on the telephone." "Then I think perhaps you ... ring me back in half an hour. By then I ... have some idea what this is all about." (можешь ли, не могу, можно мне, тебе лучше, может быть) 8. Не knows he ... read classics. He ... change to something else, (нет нужды, мог бы) 9. "Monday will be my last day in London," Hudson said. "I......stay down here fairly late." (может быть при­дется) 10. In any case, I ... not hang about outside indefinitely while the sisters finished their quarrel. They ... continue for hours, (не мог же, может быть) 11. It's too bad she ... not have a drink with us. We ... have learned a great deal about the theatre tonight, (не могла, могли бы) 12. If you help me now I......help you later, (может быть смогу) 13. "I shall wait to hear what Lily has to say about it." "You......wait a long time." (может быть, придется) 14. I think you ... certainly have told us the truth, and we ... have decided what was the best thing to do.

(следовало бы, могли бы) 15. If your mother calls, tell her I......be a

little late, (возможно придется) 16. On Saturday Charles broke the news to his father. Mr. March began to grumble: "You ... have chosen a more suitable time to tell me. You ... have known that hearing this would put me out of step for the day." (следовало бы, мог бы).