3. Put the verbs in brackets into the correct tenses. Conditional sentences: type 2.

1. If I had a typewriter I (type) it myself. 2. If I (know) his address I'd give it to you. 3. He (look) a lot better if he shaved more often. 4. If he worked more slowly he (not make) so many mistakes. 5. More tourists would come to this country if it (have) a better climate. 6. If someone (give) you a helicopter what would you do with it? 7. If he (clean) his windscreen he'd be able to see where he was going. 8. If he knew that it was dangerous he (not come). 9. The whole machine would fall to pieces if you (remove) that screw. 10. I'd go and see him more often if he (live) on a bus route.

4. Put the verbs in brackets into the correct tenses. Conditional sentences: type 3.

1. If I had known that you were in hospital I (visit) you. 2. If you (arrive) ten minutes earlier you would have got a seat. 3. I shouldn't have believed it if I (not see) it with my own eyes.4. If he had asked you, you (accept)? 5. If I (had) a map I would have been all right. 6. I (offer) to help him if I had realized that he was ill. 7. If I had realized that the traffic lights were red I (stop). 8. But for the fog we (reach) our destination ages ago. 9. If he had known that the river was dangerous he (not try) to swim across it. 10. If you (speak) more slowly he might have understood you. 11. If he had known the whole story he (not be) so angry. 12. If you (look) at the engine for a moment you would have seen what was missing.

5. Translate the sentences.

A. 1. Если бы я знал французский, я бы помог вам. 2. Если бы он был более пунктуален, с ним было бы легче иметь дело.3. Если бы он получил ваше письмо, он бы приехал раньше.4. Если бы вы не вмешались, они, возможно, спорили бы долго. 5. Если бы он был более опытен, он не сделал бы такой ошибки. 6. Если бы вы позвонили ему вчера, сейчас бы вы не волновались.

7. Жаль, что Оскара там не было. Он бы рассказал им много инте­ресных историй.

В. 1. Если бы я знал м-ра Робертсона, я бы поговорил с ним. 2. Если бы Ричард был здесь, он дал бы вам другой совет. 3. Если бы я знал, что Смиты были тогда в Париже, я бы зашел к ним. 4. Если бы старик не купил галерею, его картина не получила бы премию. 5. Если бы у него было чувство юмора, он бы не рассердился 6. Если бы вы извинились перед ним тогда, он бы на вас сейчас не сердился. 7. Почему бы вам не принять участие в завтрашнем соревновании? Вы могли бы получить приз.

Summarize the text.

Text B

Substitution Сiphers.

A substitution cipher is one in which the units of the plaintext (usually letters or numbers) are replaced with other symbols or groups of symbols. The actual order of the units of the plaintext is not changed. The simplest substitution cipher is one where the alphabet of the cipher is merely a shift of the plaintext alphabet, for example, A might be encrypted as В, С as D and so forth. Of this type of cipher, the most well-known is Caesar cipher, used by Julius Caesar in which A becomes D etc. It is easy to guess that cyclical-shift substitution ciphers of this sort are not at all secure because individual letter frequencies are left completely intact.

Product ciphers. In the days of manual cryptography i. e. without the aid of the computer product ciphers were a useful device for the cryptographer and double transposition ciphers on keyword-based matrices were, in fact, widely used. There was also some use of a particular class of product ciphers called fractionation systems. In a fractionation system a substitution is first made from symbols in the plaintext to multiple symbols (usually pairs, in which case the cipher is called bilateral cipher) in the ciphertext, which is then superencrypted by a transposi­tion.

Block ciphers. Generally, ciphers transform pieces of the plaintext of a fixed size into ciphertext. In older, manual sys­tems, these pieces were usually single letters or characters (or sometimes, as in the Playfair cipher, digraphs), since these were the largest units that could be easily encrypted or decrypted by hand. Although systems which operated on sets of three charac­ters and other, larger groups of numbers were proposed and un­derstood to potentially be more secure they were implemented because of the extra difficulty in the manual encryption or de­cryption process. In modern, single key cryptography however, the units of information can be much larger.

A block cipher is a type of symmetric-key encryption al­gorithm that changes a fixed-length block of the plain text into the same length of cipher text. The encryption works by means of a key. Decryption is a simply the reverse of the encryption process using the same secret key. The fixed length is called the block size and for modern block ciphers is usually 64 bits. As processors become more sophisticated, however, it is likely that this "block” size will increase to 128 bits.

Stream ciphers. A stream cipher also breaks the plaintext into units, this time it is normally a single character. It then en­crypts the n* unit of the plaintext with the в* unit of the key stream. Stream ciphers can be designed to be exceptionally fast, much faster than any block cipher. While the encryption of any particular plaintext with a block cipher will result in the same ciphertext when the same key is used. With a stream cipher, the transformation of the smaller plaintext units will vary, depending on when they are encountered during the encryption process.

A stream cipher generates what is known as a keystream — a sequence of bits, which is used as a key. The encryption process involves combining the keystream with the plaintext. The keystream can be generated in two ways.

1. Independent of the plaintext and ciphertext (this yields what is known as a synchronous stream cipher).

2. Depending on the data and its encryption(in which case the stream cipher is said to be self-synchronising).

In a chosen plaintext attack the cryptanalyst has the capa­bility to find the ciphertext corresponding to an arbitrary plain­text message of his or her own choosing. The likelihood of this type of attack being possible is not much. Codes which can sur­vive this attack are considered to be very secure.

In a chosen ciphertext attack the cryptanalyst can choose an arbitrary cipher-text and find the corresponding decrypted plaintext. This attack can be used in public key systems, where it may reveal the private key.

In an adaptive chosen plaintext attack the cryptoanalyst can determine the ciphertext of chosen plaintexts in an iterative process based on previous results. This is the general name for a method of attacking product ciphers called "differential cryptoanalysis".

Read the text and speak about the types of cryptoanalysis.

Text C

Types of cryptoanalysis.

There are several distinct types of cryptoanalytic attack. The type used depends on the type of cipher and how much information the cryptoanalyst has.

Types of cryptoanalytic attacks. A standard cryptoana­lytic is to determine the key which maps a known plaintext to a known ciphertext. This plaintext can be known because it is standard or because it is guessed. If the plaintext segment is guessed it is unlikely that its exact position is known however a message is generally short

enough for a cryptoanalyst to try all possible positions in parallel. In some systems a known cipher-text-plaintext pair will compromise the entire system however a strong encryption algorithm will be unbreakable under this type of attack.

A brute force attack requires a large amount of computing power and a large amount of time to run. It consists of trying all possibilities in a logical manner until the correct one is found. For the majority of the encryption algorithms a brute force at­tack is impractical due to the large number of possibilities.

Another type of brute force attack is a dictionary attack. This essentially involves running through a dictionary of words in the hope that the key (or the plaintext) is one of them. This type of attack is often used to determine passwords since people usually use easy to remember words.

In a ciphertext only attack the cryptanalyst has only the encoded message from which to determine the plaintext, with no knowledge whatsoever of the actual message. A ciphertext only attack is presumed to be possible, if not easy. In fact, an encryption techniques resistance to a ciphertext only attack is considered the basis for its cryptographic security.

Supplementary reading.

Text D

Public Key Criptography.

Since the invention of public key cryptography in 1976 by Whitfield Diffie and Martin Hellman, numerous public-key cryptographic systems have been proposed. All of these systems rely on the difficulty of a mathematical problem for the security.

Before cryptographic systems and the corresponding math­ematical problems can be discussed, the difficulty of a problem must be defined. What does it mean for a mathematical problem to be difficult? To explain this concept, the notion of an algo­rithm is required. An algorithm is a process which describes the steps to take to solve a problem. For example, in high school everyone is taught an algorithm for adding two numbers — sim­ply a sequence of steps which takes as input two numbers a and b, to be added, and outputs their sum a+b. Now mathematical problem is difficult if the fastest algorithm to solve the problem takes a long time relative to the input size.

To analyze how long an algorithm takes, computer sci­entists introduced the idea of polynomial time algorithms and exponential time algorithms. Roughly speaking, an algorithm runs quickly relative to the size of its input if it is a polynomial time algorithm, and slowly if it is an exponential time algo­rithm. Therefore, easy problems equate with polynomial time algorithms, and difficult problems equate with exponential time algorithms.

It is important to notice the words "relative to the input size" in the definition of polynomial time and exponential time algorithms. All problems are straightforward to solve if the input size is very small, but we are interested in how much harder a problem gets as the size of the input grows. For exam­ple, adding 2 and 12 to get 14 is straightforward, as is factor­ing 15 as 3x5.

However, addition is an example of an easy problem, because there is an algorithm to add numbers which runs in polynomial time, meaning that it would not take very long to add two enor­mous numbers. On the other hand, factoring is a hard problem be­cause, in general, factoring i\ large number takes a very long lime. Thus, when looking for a mathematical problem on which to base a public-key cryptographic system, cryptographers are searching for a problem for which the fastest algorithm takes exponential time. In broad terms, the longer it takes to compute the best algorithm for a problem, the more secure a public-key cryptosystem based on that problem will be.

The use of public-key cryptography is quite simple. Sup­pose Alice wants to communicate with Bob. Rather than Bob and Alice sharing a single secret key (as the case of symmetric key systems), Bob (the recipient of Alice's messages) instead has two keys —- a public key that is available to everyone in the world (including Trudy the intruder!) and a private key that is known only to Bob. In order to communicate with Bob, Alice first fetches Bob's public key. Alice then encrypts her message to Bob using Bob's public key and a known (e.g., standardized) encryption algorithm. Bob receives Alice's encrypted message and uses his private key and a known (e.g., standardized) de­cryption algorithm to decrypt Alice's message. In this manner, Alice can send a secret message to Bob without either of them having to have to distribute any secret keys!

GLOSSARY

The following glossary provides, for reference, brief definitions for several terms as used in this paper in the context of protecting information in computers.

Access

The ability to make use of information stored in a computer system. Used frequently as a verb, to the horror of grammarians.

Access control list

A list of principals that are authorized to have access to some object.

Authenticate

To verify the identity of a person (or other agent external to the protection system) making a request.

Authorize

To grant a principal access to certain information.

Capability

In a computer system, an unforgeable ticket, which when presented can be taken as incontestable proof that the presenter is authorized to have access to the object named in the ticket.

Certify

To check the accuracy, correctness, and completeness of a security or protection mechanism.

Complete isolation

A protection system that separates principals into compartments between which no flow of information or control is possible.

Confinement

Allowing a borrowed program to have access to data, while ensuring that the program cannot release the information.

Descriptor

A protected value which is (or leads to) the physical address of some protected object.

Discretionary

(In contrast with nondiscretionary.) Controls on access to an object that may be changed by the creator of the object.

Domain

The set of objects that currently may be directly accessed by a principal.

Encipherment

The (usually) reversible scrambling of data according to a secret transformation key, so as to make it safe for transmission or storage in a physically unprotected environment.

Grant

To authorize (q. v.).

Hierarchical control

Referring to ability to change authorization, a scheme in which the record of each authorization is controlled by another authorization, resulting in a hierarchical tree of authorizations.

List-oriented

Used to describe a protection system in which each protected object has a list of authorized principals.

Password

A secret character string used to authenticate the claimed identity of an individual.

Permission

A particular form of allowed access, e.g., permission to READ as contrasted with permission to WRITE.

Prescript

A rule that must be followed before access to an object is permitted, thereby introducing an opportunity for human judgment about the need for access, so that abuse of the access is discouraged.

Principal

The entity in a computer system to which authorizations are granted; thus the unit of accountability in a computer system.

Privacy

The ability of an individual (or organization) to decide whether, when, and to whom personal (or organizational) information is released.

Propagation

When a principal, having been authorized access to some object, in turn authorizes access to another principal.

СПИСОК ЛИТЕРАТУРЫ

1. Арбекова Е. И. Я хочу и буду знать английский. - М., Телер,1993

2. Krylova I.P. An English Practice Book. – М., Высшая школа, 1978

3. A Practical English Grammar. – M., Высшая школа, 1978

4. Сальная Л. К. английский язык для специалистов в области информационной безопасности. –М., Гелиос-АРВ 2008

5. JEROME H. SALTZER, MICHAEL D. SCHROEDER The Protection of Information in Computer Systems. - University of Virginia, Fall 2000

UNIT 1

1. Read and translate the text.

Text A

Does Anti-Virus Software Still Matter?

Using a computer without an anti-virus program? That’s like driving without a seatbelt — or jumping out of a plane without a parachute, right?

As users become more knowledgeable about safe computing practices, and as anti-virus solutions vendors ratchet up the general level of hacker hysteria, many people are reconsidering their system security options. Some computer users complain about the cost of antivirus solutions, while others are more concerned about the technology's impact on their machines. It's certainly no secret that anti-virus tools place a big strain on processor and memory resources and are capable of slowing older machines to a crawl. A growing number of computer users are thinking about giving anti-virus software the old heave-ho.

A New Vista. Antivirus software skeptics got a big boost last year when Microsoft co-president Jim Allchin stated that Windows Vista's new security features are so strong that anti-virus software is no longer required. In fact, he boldly claimed that he would have no problem letting his seven-year-old son use a Vista computer without any antivirus software installed. Allchin based his belief on Vista's formidable security arsenal. The operating system's new anti-virus features include the User Account Control, which defaults users to a nonadministrator status. Without administrative rights, users can't accidentally (or deliberately) modify system settings, malware can't alter system security settings or disable antivirus software (should it be installed), and users can't compromise the information of other users on shared computers. Microsoft also has made significant security improvements to Internet Explorer, including a new Protected Mode that can reduce the impact of malware by restricting where files can be saved without the user's consent. Additionally, Vista can clean many worms, viruses and rootkits, helping ensure the operating system's integrity and the privacy of users' data. Vista's Windows Defender helps protect host computers against pop-ups, slow performance and security threats caused by spyware and other unwanted software. Defender features Real-Time Protection, a monitoring system that recommends actions against detected spyware, and a streamlined interface that minimizes interruptions. Still, Microsoft is backing away from any claim that add-on anti-virus software isn't necessary for full system protection. In fact, the company offers its own anti-virus service in the form of Windows Live OneCare. The service, aimed at home users and small businesses, features an anti-virus program, a firewall, a backup-and-restore utility, a tune-up utility and integrated functionality with Windows Defender for malware protection. Most major independent antivirus vendors also serve the Vista market, claiming their solutions fill gaps left open by Microsoft.

Beyond Vista. When it comes to non-Vista computers, the need for virus protection varies in accordance with the type of system being used. XP users, for instance, will certainly benefit from anti-virus software, since the older operating system lacks most of Vista's built-in safeguards. Many Linux users, on the other hand, feel perfectly safe running their machines without any antivirus protection. It's not that Linux features some kind of virus-proof shield; it's simply that there are so few Linux users (at least in comparison to Windows users) that most hackers can't be bothered to create Linux malware. Many Macintosh users also eschew the need for anti-virus solutions. Like their Linux counterparts, they hope that safe computing practices, combined with their systems' low profile (when compared to Windows), will keep their machines safe — or at least safe enough. So does anti-virus software still matter? Well, to quote Clint Eastwood as "Dirty Harry" Callahan: "You've got to ask yourself a question: Do I feel lucky?"

COMPREHENSION CHECK