15.12-чтение

> > **красные буквы - звук произнесён неправильно или отсутствует**
 * **жирным выделены слова с неправильным ударением** toc
 * ** подчёркивание - не справляетесь со скоростью: очень невнятное чтение или лишние паузы **

Вечтомов
Children sometimes devise " secret c o des" that use a correspondence table with which to substitute a character or symbol for each character of the original message. Th is technique is called a monoalphabetic ciph er or **simple substitution**. A substitution is __an a c ceptable__ way of encryp ting text. In this section, we study several kinds of substitution ciph ers.
 * 2.2. Substitution Ciphers**

The ** Caesar ciph er** has an __important place in history__. Julius Caesar is s ai d to have been __the first to use this sch eme,__ in which __each letter is translated__ to the letter a fixed number of plac es after it in the alphabet. Caesar used a shi f t of 3, so plaintext letter pi was enciphered as ciphertext letter ci by the rule
 * The CaesarCiph er**

Казаков
Подчёркнутые фрагменты прочитаны медленно, невнятно и с лишними паузами. Children sometimes devise "secret c o des" that use a correspondence table with which to substitute a character or symbol for each character of the original message. __This techniq**ue** is called a monoa l phabetic c i pher or **simple substitution**. A substitution is an a c ceptable way of encrypting text__. In this section, we study several kinds of __substitution c i phers__. The Cae sar C i pher __The ** Cae sar c i pher** has an important place in history. Julius C ae sar is said to have been the first to use this sch eme__,
 * 2.2.Substitution C i phers**

Абраров
Слишком низкая скорость чтения. После каждого слова пауза, слитность отсутствует. Некоторые слова прочитаны по слогам. M o st c i phe r s, and e specially the ea rly ones, had to be easy to perform in the f ie ld. In pa r ticular, it was dangerous to have the cryptosystem algori th ms written down fo r the soldiers or spies to follow. Any ciphe rth at was so complicated th at its algori th m had to be written out was at risk of being rev ea l e d if the inte r ceptor c au ght a sender with the written instructions. Then, the interceptor c ou ld readily dec o de any ciphertext messag es intercepted (until the encryption algorithm c ou ld be changed).
 * Advantages and Disadvantages of the Caesar Cipher**

Макарихина
Низкая скорость чтения. The Cae sar cipher is quite simple. During Cae sar's lifetime, the simplicity did not dramatically compromise the safety of the encryption because anythin g written, even in plaintext, was r a ther well protected; few people knew how to r ea d! The pattern pi +3 __was easy to memorize__ and implement. __A sender in the field could write out a plaintext and a cipher text alphabet__, encode a message to be sent, and then destroy the paper containing the alphabets.

Цыкарев
Arrested in Si c ily in April 2006, __the reputed head of an Italian Mafia family__, Bernardo Provenzano, made notes, pizzini in the Si c ilian dialect. When arrested, he left approximately 350 of the notes behind. In the pizzini he gives instructions to his lie**u**tenants regarding particular people. Inst ea d of writing the name of a person, Provenzano used a variation of the C ae sar cipher in which letters were replaced by numbers: A by 4, B by 5, … Z by 24 (there are only 21 letters in the Italian alphabet). So in one of his notes the string "…I met 512151522 191212154 and we agreed that we will see each other after the holidays…," refers to Binnu Riina, __an associate__ arrested soon after Provenzano [LOR06].
 * Sidebar 2-3: Mafia Boss Uses Encryption**

Смирнов
The message has ac t ually been en cipher ed with a 27-symbol alphabet : A through Z plus the "blank" character or separator between words. As a start, assume that the coder was lazy and has all ow ed the blank to be translated to itself. If your assumption is true, __it is an exceptional__ piece of information; kn o wing where the spaces are allows us to see which are the small words. English has relatively few small words, such as am, is , to , be , he , we , and , are , you , she , and so on. Therefore, one way to attack this problem and br ea k the encryption is to substitute known short words at appropriate plac es in the ciph ertext until

Берёзкина
Look again at the c i pherte x t you are decrypting. There is a strong clue in the repeated of the word. You might use this text to guess at three-letter words that you know. For instance, two very common three-letter words having the pattern xyy are see and too ; other less common possibilities are add, odd , and off. (Of course, there are also obscure possibilities like woo or g ee, but it makes more sense to try the common cases first.) Moreover, the combination appears in the c i phertext, too, so you can determine whether the first two letters of the three-letter word also form a two-letter word. For instance, if is  ,

Ярушин
By now, you might notice that the ciphertext letters uncovered are just three position s away from their plaintext counterparts. You (and any experienced crypt analyst ) might try that same pattern on all the unmatched ciphertext. The completion of this decryption is left as an exercise. The cryptanalysis described here is ad hoc, using deduction based on g u esses instead of solid principles. But you can take a more methodical approach, considering which letters commonly start words, which letters commonly end words, and which pr**e**fixes and suffixes are common. Crypt analysts have com pile d lists of common prefixes, common suffixes, and words having particular patterns.

Нефёдов
Подчёркнутые фрагменты прочитаны неслитно. Notice that near the __end of the alphabet__ replacements are rather close, and the last seven characters map to themselves. Conv e niently, the last characters __of the alphabet__ are __among the least fr e quently used__, so this vulnerability would give little help __to an interceptor__. Still, __s i nce regularity helps an interceptor__, it is des i rable __to have a less regular rearrangement __ of the letters. One possibility is to count by threes (or fives or sevens or nines) and rearrange the letters in that order. For example, one encryption uses a table that starts with ABCDEFGHIJKLMNOPQRSTUVWXYZadgj using every third letter.