Учебно-методическое пособие Для студентов, аспирантов Таганрог 2008




НазваниеУчебно-методическое пособие Для студентов, аспирантов Таганрог 2008
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ТипУчебно-методическое пособие
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Texts

Pre-reading task.


Look at the title of the text. What information do you expect to read here? What would you like to know about steganography?


Text 1. Steganography.


Steganography is the art of covered or hidden writing. The purpose of steganography is covert communication to hide a message from a third party. This differs from cryptography, the art of secret writing, which is intended to make a message unreadable by a third party but does not hide the existence of the secret communication. Although steganography is separate and distinct from cryptography, there are many analogies between the two, and some authors categorize steganography as a form of cryptography since hidden communication is a form of secret writing (Bauer 2002). Nevertheless, this paper will treat steganography as a separate field.

Although the term steganography was only coined at the end of the 15th century, the use of steganography dates back several millennia. In ancient times, messages were hidden on the back of wax writing tables, written on the stomachs of rabbits, or tattooed on the scalp of slaves. Invisible ink has been in use for centuries—for fun by children and students and for serious espionage by spies and terrorists. Microdots and microfilm, a staple of war and spy movies, came about after the invention of photography (Arnold et al. 2003; Johnson et al. 2001; Kahn 1996; Wayner 2002).

Steganography hides the covert message but not the fact that two parties are communicating with each other. The steganography process generally involves placing a hidden message in some transport medium, called the carrier. The secret message is embedded in the carrier to form the steganography medium. The use of a steganography key may be employed for encryption of the hidden message and/or for randomization in the steganography scheme. In summary:

steganography_medium = hidden_message + carrier + steganography_key


Figure 1. Classification of Steganography Techniques (Adapted from Bauer 2002)

Figure 1 shows a common taxonomy of steganographic techniques (Arnold et al. 2003; Bauer 2002).

  • Technical steganography uses scientific methods to hide a message, such as the use of invisible ink or microdots and other size-reduction methods.

  • Linguistic steganography hides the message in the carrier in some nonobvious ways and is further categorized as semagrams or open codes.

  • Semagrams hide information by the use of symbols or signs. A visual semagram uses innocent-looking or everyday physical objects to convey a message, such as doodles or the positioning of items on a desk or Website. A text semagram hides a message by modifying the appearance of the carrier text, such as subtle changes in font size or type, adding extra spaces, or different flourishes in letters or handwritten text.

  • Open codes hide a message in a legitimate carrier message in ways that are not obvious to an unsuspecting observer. The carrier message is sometimes called the overt communication, whereas the hidden message is the covert communication. This category is subdivided into jargon codes and covered ciphers.

  • Jargon code, as the name suggests, uses language that is understood by a group of people but is meaningless to others. Jargon codes include warchalking (symbols used to indicate the presence and type of wireless network signal [Warchalking 2003]), underground terminology, or an innocent conversation that conveys special meaning because of facts known only to the speakers. A subset of jargon codes is cue codes, where certain prearranged phrases convey meaning.

  • Covered or concealment ciphers hide a message openly in the carrier medium so that it can be recovered by anyone who knows the secret for how it was concealed. A grille cipher employs a template that is used to cover the carrier message. The words that appear in the openings of the template are the hidden message. A null cipher hides the message according to some prearranged set of rules, such as "read every fifth word" or "look at the third character in every word."

As an increasing amount of data is stored on computers and transmitted over networks, it is not surprising that steganography has entered the digital age. On computers and networks, steganography applications allow for someone to hide any type of binary file in any other binary file, although image and audio files are today's most common carriers.

Steganography provides some very useful and commercially important functions in the digital world, most notably digital watermarking. In this application, an author can embed a hidden message in a file so that ownership of intellectual property can later be asserted and/or to ensure the integrity of the content. An artist, for example, could post original artwork on a Website. If someone else steals the file and claims the work as his or her own, the artist can later prove ownership because only he/she can recover the watermark (Arnold et al. 2003; Barni et al. 2001; Kwok 2003). Although conceptually similar to steganography, digital watermarking usually has different technical goals. Generally only a small amount of repetitive information is inserted into the carrier, it is not necessary to hide the watermarking information, and it is useful for the watermark to be able to be removed while maintaining the integrity of the carrier.

Steganography has a number of nefarious applications; most notably hiding records of illegal activity, financial fraud, industrial espionage, and communication among members of criminal or terrorist organizations (Hosmer and Hyde 2003).


What is the purpose of steganography?

How is steganography related to cryptography?

What was the early use of cryptography?

What is carrier? Steganography medium?

What is the application of steganography nowadays?


Text 2. Read the text andsummarize its ideas.

Null Ciphers

Historically, null ciphers are a way to hide a message in another without the use of a complicated algorithm. One of the simplest null ciphers is shown in the classic examples below:

PRESIDENT'S EMBARGO RULING SHOULD HAVE IMMEDIATE NOTICE. GRAVE SITUATION AFFECTING INTERNATIONAL LAW. STATEMENT FORESHADOWS RUIN OF MANY NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT IMMENSELY.

APPARENTLY NEUTRAL'S PROTEST IS THOROUGHLY DISCOUNTED AND IGNORED. ISMAN HARD HIT. BLOCKADE ISSUE AFFECTS PRETEXT FOR EMBARGO ON BYPRODUCTS, EJECTING SUETS AND VEGETABLE OILS.

The German Embassy in Washington, DC, sent these messages in telegrams to their headquarters in Berlin during World War I (Kahn 1996). Reading the first character of every word in the first message or the second character of every word in the second message will yield the following hidden text:

PERSHING SAILS FROM N.Y. JUNE 1

On the Internet, spam is a potential carrier medium for hidden messages. Consider the following:

Dear Friend , This letter was specially selected to be sent to you ! We will comply with all removal requests ! This mail is being sent in compliance with Senate bill 1621 ; Title 5 ; Section 303 ! Do NOT confuse us with Internet scam artists . Why work for somebody else when you can become rich within 38 days ! Have you ever noticed the baby boomers are more demanding than their parents & more people than ever are surfing the web ! Well, now is your chance to capitalize on this ! WE will help YOU sell more & SELL MORE . You can begin at absolutely no cost to you ! But don't believe us ! Ms Anderson who resides in Missouri tried us and says "My only problem now is where to park all my cars" . This offer is 100% legal . You will blame yourself forever if you don't order now ! Sign up a friend and your friend will be rich too . Cheers ! Dear Salaryman , Especially for you - this amazing news . If you are not interested in our publications and wish to be removed from our lists, simply do NOT respond and ignore this mail ! This mail is being sent in compliance with Senate bill 2116 , Title 3 ; Section 306 ! This is a ligitimate business proposal ! Why work for somebody else when you can become rich within 68 months ! Have you ever noticed more people than ever are surfing the web and nobody is getting any younger ! Well, now is your chance to capitalize on this . We will help you decrease perceived waiting time by 180% and SELL MORE . The best thing about our system is that it is absolutely risk free for you ! But don't believe us ! Mrs Ames of Alabama tried us and says "My only problem now is where to park all my cars" . We are licensed to operate in all states ! You will blame yourself forever if you don't order now ! Sign up a friend and you'll get a discount of 20% ! Thanks ! Dear Salaryman , Your email address has been submitted to us indicating your interest in our briefing ! If you no longer wish to receive our publications simply reply with a Subject: of "REMOVE" and you will immediately be removed from our mailing list . This mail is being sent in compliance with Senate bill 1618 , Title 6 , Section 307 . THIS IS NOT A GET RICH SCHEME . Why work for somebody else when you can become rich within 17 DAYS ! Have you ever noticed more people than ever are surfing the web and more people than ever are surfing the web ! Well, now is your chance to capitalize on this ! WE will help YOU turn your business into an E-BUSINESS and deliver goods right to the customer's doorstep ! You are guaranteed to succeed because we take all the risk ! But don't believe us . Ms Simpson of Wyoming tried us and says "Now I'm rich, Rich, RICH" ! We assure you that we operate within all applicable laws . We implore you - act now ! Sign up a friend and you'll get a discount of 50% . Thank-you for your serious consideration of our offer .

This message looks like typical spam, which is generally ignored and discarded. This message was created at spam mimic, a Website that converts a short text message into a text block that looks like spam using a grammar-based mimicry idea first proposed by Peter Wayner (spam mimic 2003; Wayner 2002). The reader will learn nothing by looking at the word spacing or misspellings in the message. The zeros and ones are encoded by the choice of the words. The hidden message in the spam carrier above is:

Meet at Main and Willard at 8:30

Special tools or skills to hide messages in digital files using variances of a null cipher are not necessary. An image or text block can be hidden under another image in a PowerPoint file, for example. Messages can be hidden in the properties of a Word file. Messages can be hidden in comments in Web pages or in other formatting vagaries that are ignored by browsers (Artz 2001). Text can be hidden as line art in a document by putting the text in the same color as the background and placing another drawing in the foreground. The recipient could retrieve the hidden text by changing its color (Seward 2004). These are all decidedly low-tech mechanisms, but they can be very effective.

Digital Image and Audio

Many common digital steganography techniques employ graphical images or audio files as the carrier medium. It is instructive, then, to review image and audio encoding before discussing how steganography and steganalysis works with these carriers.

Figure 2 shows the RGB color cube, a common means with which to represent a given color by the relative intensity of its three component colors—red, green, and blue—each with their own axis (moreCrayons 2003). The absence of all colors yields black, shown as the intersection of the zero point of the three-color axes. The mixture of 100 percent red, 100 percent blue, and the absence of green form magenta; cyan is 100 percent green and 100 percent blue without any red; and 100 percent green and 100 percent red with no blue combine to form yellow. White is the presence of all three colors.


Figure 2. The RGB Color Cube

Most digital image applications today support 24-bit true color, where each picture element (pixel) is encoded in 24 bits, comprising the three RGB bytes as described above. Other applications encode color using eight bits/pix. These schemes also use 24-bit true color but employ a palette that specifies which colors are used in the image. Each pix is encoded in eight bits, where the value points to a 24-bit color entry in the palette. This method limits the unique number of colors in a given image to 256 (2^8).

The choice color encoding obviously affects image size. A 640 X 480 pixel image using eight-bit color would occupy approximately 307 KB (640 X 480 = 307,200 bytes), whereas a 1400 X 1050 pix image using 24-bit true color would require 4.4 MB (1400 X 1050 X 3 = 4,410,000 bytes).

Color palettes and eight-bit color are commonly used with Graphics Interchange Format (GIF) and Bitmap (BMP) image formats. GIF and BMP are generally considered to offer lossless compression because the image recovered after encoding and compression is bit-for-bit identical to the original image (Johnson and Jajodia 1998A).

The Joint Photographic Experts Group (JPEG) image format uses discrete cosine transforms rather than a pix-by-pix encoding. In JPEG, the image is divided into 8 X 8 blocks for each separate color component. The goal is to find blocks where the amount of change in the pixel values (the energy) is low. If the energy level is too high, the block is subdivided into 8 X 8 subblocks until the energy level is low enough. Each 8 X 8 block (or subblock) is transformed into 64 discrete cosine transforms coefficients that approximate the luminance (brightness, darkness, and contrast) and chrominance (color) of that portion of the image. JPEG is generally considered to be lossy compression because the image recovered from the compressed JPEG file is a close approximation of, but not identical to, the original (Johnson and Jajodia 1998A; Monash University 2004; Provos and Honeyman 2003).

Audio encoding involves converting an analog signal to a bit stream. Analog sound—voice and music—is represented by sine waves of different frequencies. The human ear can hear frequencies nominally in the range of 20-20,000 cycles/second (Hertz or Hz). Sound is analog, meaning that it is a continuous signal. Storing the sound digitally requires that the continuous sound wave be converted to a set of samples that can be represented by a sequence of zeros and ones.

Analog-to-digital conversion is accomplished by sampling the analog signal (with a microphone or other audio detector) and converting those samples to voltage levels. The voltage or signal level is then converted to a numeric value using a scheme called pulse code modulation. The device that performs this conversion is called a coder-decoder or codec.

Pulse code modulation provides only an approximation of the original analog signal, as shown in Figure 4. If the analog sound level is measured at a 4.86 level, for example, it would be converted to a five in pulse code modulation. This is called quantization error. Different audio applications define a different number of pulse code modulation levels so that this "error" is nearly undetectable by the human ear. The telephone network converts each voice sample to an eight-bit value (0-255), whereas music applications generally use 16-bit values (0-65,535) (Fries and Fries 2000; Rey 1983).


Figure 4. Simple Pulse Code Modulation

Analog signals need to be sampled at a rate of twice the highest frequency component of the signal so that the original can be correctly reproduced from the samples alone. In the telephone network, the human voice is carried in a frequency band 0-4000 Hz (although only about 400-3400 Hz is actually used to carry voice); therefore, voice is sampled 8,000 times per second (an 8 kHz sampling rate). Music audio applications assume the full spectrum of the human ear and generally use a 44.1 kHz sampling rate (Fries and Fries 2000; Rey 1983).

The bit rate of uncompressed music can be easily calculated from the sampling rate (44.1 kHz), pulse code modulation resolution (16 bits), and number of sound channels (two) to be 1,411,200 bits per second. This would suggest that a one-minute audio file (uncompressed) would occupy 10.6 MB (1,411,200*60/8 = 10,584,000). Audio files are, in fact, made smaller by using a variety of compression techniques. One obvious method is to reduce the number of channels to one or to reduce the sampling rate, in some cases as low as 11 kHz. Other codecs use proprietary compression schemes. All of these solutions reduce the quality of the sound.

Table 1: Some Common Digital Audio Formats (Fries and Fries 2000)

Audio Type




File Extension




Codec



AIFF (Mac)



.aif, .aiff



Pulse code modulation (or other)

AU (Sun/Next)

.au

µ-law (or other)

CD audio (CDDA)

n/a

Pulse code modulation

MP3

.mp3

MPEG Audio Layer III

Windows Media Audio

.wma

Microsoft proprietary

QuickTime

.qt

Apple Computer proprietary

RealAudio

.ra, .ram

Real Networks proprietary

WAV

.wav

Pulse code modulation (or other)



Vocabulary tasks


Give as many word combinations as possible and translate them.

Steganography

Cipher


Make the word combinations.

  1. digital a) communication

  2. size-reduction b) code

  3. covert c) application

  4. open d) fraud

  5. nefarious e) text

  6. nonobvious f) watermarking

  7. cue g) a message

  8. convey h) method

  9. carrier i) code

  10. financial j) way


Complete the text using the terms and word combinations given below.

Apparent message, covered, illegal, a transport layer, the visible lines, suspicion.

The word "Steganography" is of Greek origin and means " … or hidden writing". Its ancient origins can be traced back to 440 BC. Generally, a steganographic message will appear to be something else: a picture, an article, a shopping list, or some other message. This … is the covertext. For instance, a message may be hidden by using invisible ink between … of innocuous documents.

The advantage of steganography over cryptography alone is that messages do not attract attention to themselves, to messengers, or to recipients. An unhidden coded message, no matter how unbreakable it is, will arouse … and may in itself be incriminating, as in countries where encryption is ….

Steganography used in electronic communication include steganographic coding inside of …, such as an MP3 file, or a protocol, such as UDP.

Translate into Russian the following passage.

Like many security tools, steganography can be used for a variety of reasons, some good, some not so good. Legitimate purposes can include things like watermarking images for reasons such as copyright protection. Digital watermarks (also known as fingerprinting, significant especially in copyrighting material) are similar to steganography in that they are overlaid in files, which appear to be part of the original file and are thus not easily detectable by the average person. Steganography can also be used as a way to make a substitute for a one-way hash value (where you take a variable length input and create a static length output string to verify that no changes have been made to the original variable length input). Further, steganography can be used to tag notes to online images (like post-it notes attached to paper files). Finally, steganography can be used to maintain the confidentiality of valuable information, to protect the data from possible sabotage, theft, or unauthorized viewing.


Translate into English the following passage.

В настоящее время компьютерные технологии придали новый импульс развитию и совершенствованию стеганографии, появилось новое направление в области защиты информации — компьютерная стеганография. Учитывая естественные неточности устройств оцифровки и избыточность аналогового видео- или аудиосигнала, методы компьютерной стеганографии позволяют скрывать сообщения в компьютерных файлах и потоках данных. Причем, в отличие от криптографии, данные методы скрывают сам факт передачи информации. Стеганография занимает свою нишу в обеспечении безопасности: она не заменяет, а дополняет криптографию. Сокрытие сообщения методами стеганографии значительно снижает вероятность обнаружения самого факта передачи сообщения, при этом шифрование сообщения обеспечивает его конфиденциальность и имитостйкость в случае обнаружения. Преимущества компьютерной стеганографии привели к появлению программных решений, использующих методы стеганографии для организации скрытых каналов передачи и информации и её хранения. В связи с возрастанием роли глобальных компьютерных сетей становится все более важным и значение стеганографии. В настоящее время можно выделить четыре тесно связанных между собой и имеющих одни корни направления приложения стеганографии:

  • защита конфиденциальной информации от несанкционированного доступа;

  • преодоление систем мониторинга и управления сетевыми ресурсами;

  • камуфлирование программного обеспечения;

  • защита авторского права на некоторые виды интеллектуальной собственности.



Grammar. Modal Verbs.

Употребление.

Выражение способности или умения что-либо делать.

Can- мочь, уметь, be able to- быть в состоянии.

I can't skate- Я не умею кататься на коньках.

I won't be able to run so fast- Я не смогу так быстро бежать.

Глагол can имеет форму прошедшего времени could. Все остальные времена выражаются при помощи be able to.

Выражение возможности (вероятности).

May - определенная степень вероятности,

Might - большая степень вероятности.

They may be at work- Наверно, они на работе.

There might be some sugar in the cupboard- В шкафу, кажется, есть сахар.

Must – уверенность

They look alike. They must be twins.

Они похожи внешне. Должно быть, они близнецы.

Cantкажется невозможным

You’ve been sleeping all day. You can't be tired.

Ты спишь целый день, ты не можешь устать.

Can … be – возможно ли.

Can she still be at school? Она может все еще быть в школе.

Выражение разрешения в вопросах.

Сan – неформальное.

Can I borrow your pen? Можно взять твою ручку?

Сould – более вежливое.

Could I borrow your car? Ты не мог бы дать мне твою машину?

May – формальное.

May I use your phone?

Можно воспользоваться вашим телефоном?

Might – еще более формальное.

Might I see your driving license please? Ваши права, пожалуйста.

Выражение разрешения в ответах.

Can – неформальное разрешение.

You can have my pen. Можешь взять мою ручку.

May – формальное разрешение.

You may come in. Mожете войти.

Mustn’t, сan’t – запрет.

You mustn’t park here. Парковка здесь запрещена.

You can't enter this room. Сюда нельзя.

Выражение предложения.

Would you like, shall I/ shall we – вежливое предложение.

Would you like some coffee please? Хотите кофе?

Shall we buy him a present? Купим ему подарок?

Выражение просьбы.

Сan – просьба.

Can you help me finish my work? Поможешь мне закончить работу?

Сouldвежливая просьба).

Could I have some more paper? Можно мне еще лист бумаги?

Will – неформальная просьба.

Will you help me? Ты поможешь мне?

Выражение совета.

Should/ought to, had better.

You should walk more.Тебе надо больше ходить пешком.

You'd better rewrite this passage. Тебе лучше переписать этот абзац.

Выражение долженствования (необходимости).

Mustобязанность.

We must obey the laws. Мы должны подчиняться закону.

Нave to -- необходимость, продиктованная внешними факторами.

I have to be at work at 8.30. Мне нужно быть на работе в 8.30.

I've gotнеформальное выражение личной необходимости.

I've got to leave. Мне нужно идти.

Выражение запрета.

Mustnt, сantзапрет.

You mustn’t park here. Здесь нельзя парковаться.

You can't enter this room. It's room for the staff.

Эта комната для персонала. Вам туда нельзя.

Выражение отсутствия необходимости.

Needn't, dont have toотсутствие необходимости.

You don’t need/have to do it now. Необязательно делать это сейчас.


Grammar tasks


Test A. State the function of the following modal verbs.

  1. Electronic Signatures can come in many forms.

  2. The single-photon source and the detectors must be connected by a “quantum channel”.

  3. Two forms of attack might be carried out.

  4. A DMBS application may consist of one or more executable images and one or more data files.

  5. High-quality signatures can offer authentication, integrity and non-repudation.

  6. Could you help us?

  7. Shall we stop working over this project?

Test B. Paraphrase the following sentences using the modal verbs given below.

  1. I’m sure the paper is somewhere in the office. (must)

  2. I think you are not working hard. (should)

  3. I need this job! (must)

  4. Perhaps our colleagues will come in time. It depends on the traffic. (might)


Test C. Write sentences using modal verbs and the following words.

      1. 1. The idea/machine/generate speech/be discussed/for about 50 years.

      2. The vulnerability analysis/take/five work days.

      3. Employee/change/passwords.

      4. I/help you/with the project?

      5. Excuse me! You/explain this message for me?


Communication.

You’ve received an invitation to the conference. Discuss the trip and the topic of your report with your colleagues.


Writing.

Write an abstract of the material you’d like to present at the conference.


Additional vocabulary.

  1. spam mimic – имитация спама

  2. formatting vagary – разновидность форматирования

  3. retrieve the hidden text – восстановить скрытый текст

  4. bit-for-bit identical – поразрядно идентичный

  5. discrete cosine transforms coefficient – коэффициент дискретного косинусного преобразования

  6. lossy compression - сжатие с потерей данных

  7. pulse code modulation - кодово-импульсная модуляция

  8. proprietary compression scheme – патентованная схема упаковки



Unit 6. QUANTUM CRYPTOGRAPHY


Vocabulary


What do the following terms and word combinations mean?

Eavesdrop, quantum coin flipping, quantum bit commitment, measure (v), be a bit off, rectilinear basis, random result, prearranged code.


Texts


Pre-reading task

What do you know about quantum cryptography?

Comment on the efficiency of the quantum cryptography methods.


Text 1. Quantum cryptography.

Quantum cryptography is another kind of cryptography in this world. With it, you can create a communications channel where it is impossible to eavesdrop without disturbing the transmission. The laws of physics secure this quantum channel: even if the eavesdropper can do whatever he wants, even if the eavesdropper has unlimited computing power. Charles Bennett, Gilles Brassard, Claude Crepeau and others have expanded on this idea, describing quantum key distribution, quantum coin flipping, quantum bit commitment.

According to quantum mechanics, particles don't actually exist in any single place. They exist in several places at once, with probabilities of being in different places if someone looks. However, it isn't until a scientist comes along and measures the particle that it "collapses" into a single location. But you can't measure every aspect (for example, position and speed) of a particle at the same time. If you measure one of those two quantities, the very act of measuring it destroys any possibility of measuring the other quantity. The quantum world has a fundamental uncertainty and there's no way to avoid it.

That uncertainty can be used to generate a secret key. As they travel, photons vibrate in some direction; up and down, left to right or more likely at some angle. Normal sunlight is unpolarized; the photons vibrate every which way. When a large group of photons vibrate in the same direction they are polarized. Polarization filters allow only photons that are polarized in a certain direction through; the rest are blocked. For example, a horizontal polarization filter only allows horizontally polarized photons through. Turn that filter 90 degrees, and only vertically polarized photons can come through.

Let's say you have a pulse of horizontally polarized photons. If they try to pass through a horizontally polarized filter, they all get through. Slowly turn that filter 90 degrees; the number of photons getting through gets smaller and smaller, until none get through. You'd think that turning the filter just a little will block all the photons, since the photons are horizontally polarized. But in quantum mechanics, each particle has a probability of suddenly switching its polarization to match the filter. If the angle is a little bit off, it has a high probability. If the angle is 90 degrees off, it has zero probability. And if the angle is 45 degrees off, it has a 50 percent probability of passing through the filter.


Answer the questions

What laws of physics is quantum cryptography based on? Why can't you measure every aspect of a particle at the some time? How do polarization filters work?


Text 2. Read the text and describe the process of secret key generation.

Polarization can be measured in any basis: two directions at right angles. An example basis is rectilinear: horizontal and vertical. Another is diagonal: left-diagonal and right-diagonal. If a photon pulse is polarized in a given basis and you measure it in the same basis, you learn the polarization. If you measure it in the wrong basis, you get a random result. We're going to use this property to generate a secret key:

For example: Alice and Bob are users, and Eve is an eavesdropper.

1) Alice sends Bob a string of photon pulses. Each of the pulses is randomly polarized in one of four directions: horizontal, vertical, left-diagonal, and right-diagonal.

2) Bob has a polarization detector. He can set his detector to measure rectilinear polarization or he can set his detector to measure diagonal polarization. He can't do both; quantum mechanics won't let him. Measuring one destroys any possibility of measuring the other.

Now, when Bob sets his detector correctly, he will record the correct polarization. If he sets his detector to measure rectilinear polarization and the pulse is polarized rectilinearly, he will learn which way Alice polarized the photon. If he sets his detector to measure diagonal polarization and the pulse is polarized rectilinearly, he will get a random measurement. He won't know the difference.

3) Bob tells Alice, over an insecure channel, what settings he used.

4) Alice tells Bob which settings were correct.

5) Alice and Bob keep only those polarizations that were correctly measured.

Using a prearranged code, Alice and Bob each translate those polarization measurements into bits. For example, horizontal and left-diagonal might equal one, and vertical and right-diagonal might equal zero.

So, Alice and Bob have generated bits as many as they like. On the average, Bob will guess the correct setting 50 percent of the time, so Alice has to send 2n photon pulses to generate n bits. They can use these bits as a secret key for a symmetric algorithm or they can guarantee perfect secrecy and generate enough bits for a one-time pad.

The really cool thing is that Eve cannot eavesdrop. Just like Bob, she has to guess which type of polarization to measure; and like Bob, half of her guesses will be wrong. Since wrong guesses change the polarization of the photons, she can't help introducing errors in the pulses as she eavesdrops. If she does, Alice and Bob will end up with different bit strings.

6) So, Alice and Bob compare a few bits in their strings. If there are discrepancies, they know they are being bugged. If there are none, they discard the bits they used for comparison and use the rest.

Improvement to this protocol allows Alice and Bob to use their bits even in the presence of Eve. They could compare only the parity of subsets of the bits. Then, if no differences are found, they only have to discard one bit of the subset. This detects eavesdropping with only a 50 percent probability, but if they do this with n different subsets Eve's probability of eavesdropping without detection is only 1 in 2".

There's no such thing as passive eavesdropping in the quantum world. If Eve tries to recover all the bits, she will necessarily break the communications.


Vocabulary tasks


Give English equivalent of the following Russian words and words combinations.

Неопределенность, передача (информации), возможность, под углом, в определенном направлении, избежать, проходить сквозь что-либо.


Give Russian equivalent of the following English words and words combinations.

Expand, disturb the transmission, over an insecure channel, discrepancy, the parity of subsets, discard, recover the bits.


Form different parts of speech and translate them.

Polar


Make the word combinations.

1. polarization a) channel

2. rectilinear b) of subsets

3. the parity c) bit commitment

4. communication d) on the idea

5. quantum e) channel

6. random f) polarization

7. expand g) code

8. insecure h) filter

9. pre-arranged i) polarization

10. diagonal j) result


Complete the text using the terms and word combinations given below.

An eavesdropper, guarantees, without disturbing, vulnerable, access


It is impossible to obtain information about physical system … it in a random, uncontrollable way. This fundamental quantum-mechanical law … the security of Quantum Key Exchange (QKE) protocols. QKE protocols such as BB84 have been proved to be secure under the assumption that the known laws of physics hold. Given this assumption, QKE is unconditionally secure, i.e. secure even in the presence of … with unlimited computational power.

QKE requires that the parties have … to an authentic channel. Any QKE protocol that does not fulfill this requirement is … to a man-in-the middle attack.


Translate into Russian the following passage.

Quantum Channels.

The single-photon source and the detectors must be connected by a “quantum channel”. Such a channel is not especially quantum, except that it is intended to carry information encoded in individual quantum systems. Here “individual” does not mean “nondecomposible”, but only the opposite of “ensemble”. The idea is that the information is coded in a physical system only once, in contrast to classical communication, in which many photons carry the same information. Note, that the present-day limit for fiber-based classical optical communication is already down to a few tens of photons, although in practice one usually uses many more.

Individual quantum systems are usually two-level systems, called qubits. During their propagation they must be protected from environmental noise. Here “environment” refers to everything outside the degree of freedom used for the encoding, which is not necessarily outside the physical system. If, for example, the information is encoded in the polarization state, then the optical frequencies of the photon are part of the environment. Hence coupling between the polarization and the optical frequency has to be mastered. Moreover, the sender of the qubits should avoid any correlation between the polarization and the spectrum of the photons.


Translate into English the following passage.

1. Квантово-криптографические системы - это побочный продукт разрабатываемого в настоящее время так называемого квантового компьютера.

2. Основная причина бурных исследований в области квантовых компьютеров – это естественный параллелизм квантовых вычислений.

3. Например, если квантовая память состоит из двух кубитов, то мы параллельно работаем со всеми ее возможными состояниями: 00, 01, 10, 11.

4. Бурное развитие квантовых технологий и волоконно-оптических линий связи привело к появлению квантово-криптографических систем.

5. В квантово-криптографическом аппарате применим принцип неопределенности Гейзенберга, согласно которому попытка произвести измерения в квантовой системе вносит в нее нарушения, и полученная в результате такого измерения информация определяется принимаемой стороной как дезинформация.

6. Итак, две конечных цели квантовой (как и классической) криптографии:

1) обеспечить отправителю и адресату защищенный канал обмена информацией;

2) обеспечить механизм проверки секретности такого обмена.

7. Секретным и абсолютно защищенным, в принципе, можно сделать любой канал

передачи информации.

8. Достаточно лишь чтоб обмен шел сообщениями, зашифрованными

криптостойким шифром и качественным секретным ключом.

9. Секретным считаем ключ, известный лишь отправителю и адресату. 10. Качественный ключ - представляет собой абсолютно случайную последовательность 0 и 1.


Additional Vocabulary.

    1. communications channel – канал коммуникации

    2. secure(v) - охранять

    3. expand on an idea – развить мысль

    4. quantum key distribution – распределение квантового ключа

    5. be on the lunatic fringe of cryptography – быть на периферии криптографии

    6. polarization filter - поляризационный фильтр

    7. rectilinear polarization – линейная поляризация

    8. diagonal polarization – диагональная поляризация

    9. over an insecure channel, prearranged code

    10. discrepancy - расхождение

    11. be bugged - быть под тайным наблюдением

    12. discard the bits - отвергнуть биты

    13. parity of subsets - сравнимость подмножеств по модулю



Vocabulary and Grammar 1-6. Revision.


  1. Put the words in the correct order. The first word is underlined.

  1. scientists, of, the method, frequency, using, a code, discovered, Arabic, breaking, analysis, by, was

  2. process, input, the results, are, of, valuable, the evaluation, to, the accreditation

  3. will, evaluation, the CC, between, independent, permit , the results, comparability, of, security

  4. began, hackers, in 1990, the government, campaign, to crackdown, nationwide

  5. to remain, developments, cryptology, an area, interesting, promises, of




  1. Complete the sentences using the words given below.

Block ciphers, require, were hidden, judgments, to recover, inspection, a protocol certification, jargon code, a set.

    1. The certification process is the independent ________ of the results of the evaluation leading to the production of the final certificate or approval.

    2. The CC is presented as __________ of distinct but related parts.

    3. The evaluation scheme, methodology and __________ processes are the responsibility of evaluation authorities that run evaluation scheme.

    4. Many of the evaluation criteria _________ the application of expert judgements and background knowledge for which consistency is more difficult to achieve.

    5. The CC contains criteria to be used by evaluators when forming __________ about the conformance of TOEs to the security requirements.

    6. In ancient times, messages ____________ on the back of wax writing tables.




    1. A method of encryption is only secure if even with this complete access, the eavesdropper is still unable __________ the original plaintext from the ciphertext.




    1. Kerberos is ___________ for single sign-on and authenticating users against a central authentication and key distribution server.




    1. ___________ like DES are intended to be very hard to break.




    1. ___________ , as the name suggests, uses language that is understood by a group of people but is meaningless to others.
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