Английский язык для пользователей ПК и программистов - Гольцова Е.В.
ISBN 5-7931-0086-5
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to reverse поворачивать(ся) в противоположном направлении, перевертывать
reversible —_
inverse--
to apply обращаться, прилагать, применять to compress сжимать to swap менять, обмениваться to allow позволять, разрешать
arbitrary произвольный; капризный, деспотический search поиск; искать
feasible выполнимый, осуществимый, вероятный to replace вернуть, восстановить, заменить to wrap завертывать, сворачивать, заворачивать wrap-around —_
307 Английский язык для пользователей ПК и программистов
row ряд
top row--
bottom row —_
message сообщение, послание, миссия
set набор, множество
to map наносить, накладывать
equal равный, одинаковый
clue ключ, улика, нить
to deduce выводить заключение, проследить
frequency частота
to avoid избегать
to merge поглощать, сливать(ся), соединять(ся) vulnerable уязвимый, ранимый
Упражнение 12. Translate the following form-words without a dictionary. You are to know them now.
Переведите следующие служебные, структурные слова; вы их уже должны знать.
Три-пять минут — нормальный результат.
TEST
1) according to__
2) how much_
3) in order not to___
4) in (sections) ... through ..._
5) such_
6) an example, Eg., for example_
7) that is_
8) via_
9) in the case of_
10) each of__
11) by_
12) further on_
13)thu s_
14) as if_
15) once_
16) however__
17) because_
Упражнение 13. Translate the sentences underlined in the text. Mind different functions of infinitive.
Переведите подчеркнутые в Тексте предложения. Помните о функциях инфинитива в предложении.
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Упражнение 14. The text is organized into two sections:
Текст организован в две секции: 1) Description of encryption techniques.
2) The examples of encryption techniques.
Read every section of the text. Прочтите каждую часть Текста.
Упражнение 15. Match the examples of encryption techniques and the description of it. Сопоставьте описание технологии шифрования и примеры к конкретному описанию. Вставьте номер примера в квадратные скобки в Тексте.
Text
Encryption techniques
Encryption techniques can be classified broadly according to how much of the encryption process need be kept secret in order not to compromise encrypted texts.
Clearly it is best to have to protect as little as possible of the encryption process. In sections 5.1 through 5.2 of this chapter we consider three categories of methods that require protection for respectively:
(1) The encryption algorithm;
(2) The key.
Description of encryption techniques
5 .1. Private algorithm
Our first category of methods requires that the encryption algorithm itself be kept secret (private) because knowledge of the encryption algorithm is sufficient to produce a decryption algorithm. Note that such
The examples of encryption techniques
I. Alphabet shifting
ABCDEFGHIJKff1N0PQRSTUVWXYZ
abcdefghlj klmnopqrstuvwxyz
rStuvwxyzABCDEFGHIJKLMNOPQRSTUVWxYZ
abcdefghij klmnopq
To encrypt, find the character on the top row and replace it by the corresponding character on the bottom row. To decrypt, reverse the process. Thus, for example, plaintext: This is a secret message ciphertext: KZ jR jRSRjWUiWkRdWjjSYW
II. Four-step encryption algorithm
1. Translate the text from English to Navajo.
2. Write the input row-by-row in a matrix of a certain size, output the matrix column-by-column.
3. Compress the file using Huffman ceding.
4. Swap disjoint pairs of bytes
309 Английский язык для пользователей ПК и программистов
an algorithm typically does not use a key as described above. For example, encryption may consist of a sequence of reversible steps. If the steps were known, the inverse operations could simply be applied in the reverse order to decrypt a ciphertext. An example of a four-step algorithm is shown in section of examples. [ ]
5.2 Public algorithm, private key
Our second category of methods does not require that the encryption algorithm be kept secret. Knowledge of the algorithm may allow a more focussed attack on a ciphertext but is not by itself sufficient. An arbitrary ciphertext file is protected by keeping secret the key needed to decrypt it. The size of the key space, that is the number of possible keys, is important in any encryption technique that uses keys. It should not be feasible for an attacker to decrypt a ciphertext via a direct search of the key space. In the case of each of the algorithms discussed in this section, the key to encrypt a file is also used to decrypt it.
5.2.1 Caesar code
To encrypt a file, replace each character by the character ^ further on in the (wrap-around) alphabet. An example shows an alphabet and the alphabet shifted 9 places. [ ]
This method is easily attacked- because of the small set of keys; the number of effective keys is the same as the size of the alphabet.
5.2.2 Simple substitution code
Suppose we write out the alphabet, as in the top row of example, and make the bottom row a permutation of it. In the second section an example is shown. [ ]
