Computer Science. The English Language Perspective - Беликова (1176925), страница 31
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When properly implemented, a digital signature givesthe recipient of a message reason to believe the messagewas sent by the claimed sender. Digital signatures arevery useful when sending sensitive email and othertypes of digital communication.6. Plaintext is any information before it has beenencrypted.7. Ciphertext is the output information of an encryptioncipher.8. Due to the tremendous advantage of knowing theenemy's thoughts, war is the main driving force ofcryptanalysis.9.
Throughout history many governments have employeddivisions solely for cryptanalysis during war time.2. Answer the following questions:1. What is the difference between cryptography andcryptanalysis?2. How can encryption be used in everyday life?3. What does the operation of the cipher depend on?4. What are the interrelations of a plaintext and ciphertext?5. What is the main driving force of cryptanalysis?3. Translate into English:Криптография — наука о математических методахобеспечения конфиденциальности и аутентичностиинформации. Изначально криптография изучала методышифрования информации — обратимого преобразованияоткрытого (исходного) текста на основе секретногоалгоритма и/или ключа в шифрованный текст(шифртекст).
Традиционная криптография образует184разделсимметричныхкриптосистем,вкоторыхзашифрованиеирасшифрованиепроводитсясиспользованием одного и того же секретного ключа.Помимо этого раздела современная криптографиявключает в себя асимметричные криптосистемы, системыэлектроннойцифровойподписи,хеш-функции,управление ключами, получение скрытой информации,квантовую криптографию.Криптоанализ — наука о методах получения исходногозначения зашифрованной информации, не имея доступа ксекретной информации (ключу), необходимой для этого. Вбольшинствеслучаевподэтимподразумеваетсянахождениеключа.Внетехническихтерминах,криптоанализ есть взлом шифра (кода).Под термином «криптоанализ» также понимаетсяпопытканайтиуязвимость в криптографическомалгоритме или протоколе. Результаты криптоанализаконкретного шифра называют криптографической атакойна этот шифр. Успешную криптографическую атаку,полностьюдискредитирующуюатакуемыйшифр,называют взломом или вскрытием.4.
Give the summary of the text using the key terms.HISTORICAL CRYPTOGRAPHYRead the following words and word combinations and usethem for understanding and translation of the text:scribe - переписчикinscription - надписьsubstitution cipher - подстановочный шифрparchment - пергаментto wind - наматыватьlength-wise - по длине185a transposition cipher - перестановочный шифрto overtake - опережатьgrid - решеткаoffset - сдвинутыйgibberish - бессмысленныйto intercept - перехватыватьbrute force method - подбор методом грубой силыoverconfidence - самонадеянностьto map - преобразоватьstepping switch - шаговый переключательrenowned - прославленныйAncient EgyptThe earliest known text containing components ofcryptography originates in the Egyptian town Menet Khufu onthe tomb of nobleman Khnumhotep II nearly 4,000 years ago.
Inabout 1900 B.C. Khnumhotep's scribe drew his master's life inhis tomb. As he drew the hieroglyphics he used a number ofunusual symbols to obscure the meaning of the inscriptions.This method of encryption is an example of a substitutioncipher, which is any cipher system which substitutes onesymbol or character for another.As the Egyptian culture evolved, hieroglyphic substitutionbecame more common. This method of encryption wasrelatively easy to break for those who could read and write.There are several possibilities why the Egyptians would use thesacred nature of their religious rituals from commoncryptography is that the scribes wanted to give a formalappearance to their writings.
This seems to be very similar toformal complicated language used in any modern legaldocument. Egyptian cryptography could also have been a wayfor a scribe to impress others by showing that he could write ata higher level.186GreeceIn about 500 B.C. the Spartans developed a device calledScytale, which was used to send and receive secret messages.The device was a cylinder in which a narrow strip of parchmentwas wound. The message was then written length-wise on theparchment. Once it was unwound the message on the strip ofparchment became unreadable.
To receive the message anidentical cylinder was needed. It was only then that the letterswould line up resulting in the original message.The Scytale is an example of a transposition cipher, which isany cipher system that changes the order of the charactersrather than changing the characters themselves. In today'sstandards, the Scytale would be very easy to decipher,however, 2,500 years ago the percent of people that could readand write was relatively small. The Scytale provided theSpartans a secure method of communication.RomeThe earliest recorded military use of cryptography comes fromJulius Caesar 2,000 years ago. Caesar, being commander of theRoman army, solved the problem of secure communicationwith his troops.
The problem was that messengers of secretmilitary messages were often overtaken by the enemy. Caesardeveloped a substitution cipher method in which he wouldsubstitute letters for different letters. Only those who knew thesubstitution used could decipher the secret messages. Nowwhen the messengers were overtaken the secret messages werenot exposed. This gave the Roman army a huge advantageduring war.Caesar typically just shifted his letters by some predeterminednumber. This number was the cipher key of his algorithm. Arandomized order of substitution yields a much larger amountof security due to the larger amount of possible orderings.187Alberti-Vigenere CipherDuring the mid 1400s a man named Leon Battista Albertiinvented an encryption system using a cipher disk.
This was amechanical device with sliding disks that allowed for manydifferent methods of substitution. This is the base concept of apolyalphabetic cipher, which is an encryption method whichswitches through several substitution ciphers throughoutencryption. Alberti never developed his cipher disk concept.In the 1500s Blaise De Vigenere, following Alberti'spolyalphabetic cipher style, created a cipher that came to beknown as the Vigenere Cipher. The Vigenere Cipher worksexactly like the Caesar except that it changes the keythroughout the encryption process. The Vigenere Cipher uses agrid of letters that give the method of substitution.
This grid iscalled a Vigenere Square or a Vigenere Table. The grid is madeup of 26 alphabets offset from each other by one letter.The method of changing from one key to another follows onesimple pattern. The encryption key was chosen as a specialsecret word.
The corresponding letter is then substituted for theplaintext character. This method is repeated through allcharacters of the key word. After all characters of the key wordare used, the word is just repeated.Jefferson Wheel CipherIn the late 1700s, Thomas Jefferson came up with a ciphersystem very similar to the Vigenere Cipher except with highersecurity. His invention was 26 wheels with the alphabetrandomly scattered on each wheel. The wheels were numberedand ordered with a specified order.
This order is the key to theencryption algorithm.To message to be encrypted on the wheels lining up is made onthe wheels such that the message is present. The ciphertext isany other line besides the line containing the original message.The person decrypting the ciphertext must have the wheels inthe proper order. As the ciphertext is made on the wheels, theplaintext is lined up somewhere else on the wheels. A visual188scan can quickly result in finding the original text. There is anextremely small chance that two non-gibberish messages willemerge on the disk during decryption.Zimmerman TelegramIn early 1917, during the early stages of World War I, Britishcryptographers encountered a German encoded telegram.
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