Goal of the work: familiarization with the simplest techniques for encrypting text information.

Theoretical information

Diplomatic, military and industrial secrets are usually transferred or stored not in their original form, but after encryption. Unlike secret writing, which hides the very fact of the presence of a message, encryption is transmitted openly, but the meaning itself is hidden. So, cryptography ensures that the meaning of a message is hidden using encryption and opened by decryption, which are performed using special cryptographic algorithms using keys from the sender and recipient.

Caesar Cipher

The Caesar cipher is one of the oldest ciphers. When encrypting, each character is replaced by another, spaced from it in the alphabet by a fixed number of positions. The Caesar cipher can be classified as a substitution cipher, with a narrower classification as a simple substitution cipher.

The cipher is named after the Roman emperor Gaius Julius Caesar, who used it for secret correspondence. Natural development The Caesar cipher became the Vigenère cipher. From the point of view of modern cryptanalysis, the Caesar cipher does not have acceptable strength.

The essence of the cipher is to replace each letter with a letter located 3 positions to the right from it in the alphabet (any key can be selected). Such ciphers, based on replacing some letters with others, are called substitution ciphers. Monoalphabetic ciphers (which include the Caesar cipher) are a type of substitution cipher in which each letter in the plaintext always corresponds to the same letter in the ciphertext.

Figure 1 Caesar Cipher

Letter
Letter
Letter

Example:

It is necessary to encrypt the message using the Caesar method.

Original post: "Cryptography"

Message

Number 1 + 3

Number 1 – letter number according to table.

Number 1+3 – letter number according to table. + key (move the letter 3 positions forward)

Answer: "Nulthseugchlv"

The advantage of the Caesar encryption system is the ease of encryption and decryption. The disadvantages of Caesar's system include the following:

Substitutions performed according to the Caesar system do not mask the frequencies of occurrence of various letters in the original plaintext;

The alphabetical order in the sequence of replacement letters is maintained;

The Caesar cipher can be easily broken by analyzing the frequency of occurrence of letters in the ciphertext.

However, the concept inherent in the Caesar encryption system turned out to be very fruitful, as evidenced by its numerous modifications.

Goal of the work: familiarization with the simplest techniques for encrypting and decrypting text information.

Exercise 1

Caesar's cipher. This cipher implements the following text transformation: each letter of the original text is replaced by the next letter after it in the alphabet, which is considered to be written in a circle.
Using the Caesar cipher, encrypt the following phrases:
a) Time for business - time for fun
b) Happy New Year
c) First of September

Task 2

Using the Caesar cipher, decode the following phrases:
a) Lmbttoyk shbt
b) Vömpö tpmöchö rftuyoj

Task 3

Vigenère cipher. This is a Caesar cipher with a variable shift value. The shift amount is specified using a keyword. For example, the keyword VASE means the following sequence of letter shifts in the source text: 3 1 9 1 3 1 9 1, etc. Using WINTER as the keyword, encode the words: ALGORITHMIZATION, COMPUTER, INTERNET.

Task 4

The word ZHPUSHCHEB was obtained using the Vigenère cipher with the keyword BANK. Restore the original word.

Task 5*

Using the Excel spreadsheet processor, automate the process of encoding words using the keyword bank (it is assumed that the words will consist only of lowercase Latin letters and their length will not exceed 10 characters). To solve the problem, use the text functions SYMBOL and CODE SYMBOL. Each letter must be stored in a separate cell. The shift value should be determined automatically (the code of the letter of the keyword minus the code of the letter “a” plus one). Try to encrypt the words using your table: algebra, geometry, english.

Task 6

Using the location of the letters on your computer keyboard as a key, decode the message:
D ktce hjlbkfcm `kjxrf?
D ktce jyf hjckf?

Task 7

Using the location of the letters on your computer keyboard as a key, encode the message:
Moscow is capital of Russia.

Task 8

Rearrangement cipher. Coding is carried out by rearranging letters in a word according to the same rule. Restore the words and determine the permutation rule:
NIMAREL, LETOFEN, NILKYEA, NOMOTIR, RAKDNASHA.

Task 9

Using the above permutation cipher, encode the following words: HORIZON, TV, TAPE.

Task 10

Determine the rule for encrypting and decrypting a word:
KERNOTSLITKELUONPIEZhDAIFYA
UKROGREOSHLAEKVISCHTEVMO

Lesson topic:"Information encryption"

Item: Computer science

Group: II year groups (11th grade)

Keywords: practical work, encryption, information protection, cryptography, Caesar method, Microsoft Excel

Equipment: computer class, Microsoft program Office, task cards (see appendix)

Literature:

1. Melnikov V.P., Kleimenov S.A., Petrakov A.M. Information Security: tutorial for students prof. education. – M.: Publishing House “Academy”, 2009.

2. Alferov A.P., Zubov A.Yu., Kuzmin A.S., Cheremushkin A.V. Fundamentals of cryptography: tutorial. – M.: Gelios ARV, 2002.

Lesson type: practical work

Form of work: individual on computer

Annotation: task completion time – 90 minutes. (1 pair)

The purpose of the lesson: studying the simplest methods of cryptographic protection of information and strengthening skills in working in a software environmentMicrosoftExcel.

During the classes:

Studying theoretical material.

Encrypting your last name and first name using the Caesar method and Microsoft Excel.

Deciphering a phrase from a card using the Caesar method and Microsoft Excel.

Encrypt the phrase decrypted in step 4 using the permutation method with a key. Use your last name as a key.

Answer questions orally.

Present your work to the teacher.

Theoretical information:

Caesar Cipher System – special case simple substitution cipher. The method is based on replacing each character of the message (plaintext) with another character of the same alphabet, by shifting from the original one to k positions (we get the closed text). Magnitude k is called a cipher key (the key is the information necessary to smoothly decrypt the information). The key to Caesar's method is an integer. If you assign a number to each character of the alphabet used, the encryption process will proceed according to the formula:

Where x i– number of the i-th character in plain text, y i– number of the i-th character in the closed text, k- key, n– number of characters in the alphabet. The mod operation is taking the remainder when dividing one number by another (for example: 5 mod 2 = 1, 10 mod 5 = 0, 20 mod 7 = 6).

Decryption (decoding) will take place according to the formula

Example.

Let's encrypt the word " using the Caesar method with key k = 7 cipher».

We will use the Russian alphabet without the letter ё, where the letter A corresponds to the number 0, and therefore the letter Z corresponds to 31. That is n=32.

We'll put it in original word Each letter corresponds to a number:

 24

X 1

 8

X 2

 20

X 3

 16

X 4

Then y 1 = (x 1 + k) mod 32 = (24 +7) mod 32 = 31 mod 32 = 31 I

y 2 = (x 2 + k) mod 32 = (8 +7) mod 32 = 15 mod 32 = 15 p

y 3 = (x 3 + k) mod 32 = (20 +7) mod 32 = 27 mod 32 = 27 s

y 4 = (x 4 + k) mod 32 = (16 +7) mod 32 = 23 mod 32 = 23 h

Thus, we got the word “ yapych»

Decryption.

For decryption it is necessary for each character of the word " yapych» match the number:

 31

= y 1

 15

= y 2

 27

= y 3

 23

= y 4

Then x 1 = (y 1 + (32 – k)) mod 32 = (31 +(32 – 7)) mod 32 = 56 mod 32 = 24 w

x 2 = (y 2 + (32 – k)) mod 32 = (15 +25) mod 32 = 40 mod 32 = 8 and

x 3 = (y 3 + (32 – k)) mod 32 = (27 +25) mod 32 = 52 mod 32 = 20 f

x 4 = (y 4 + (32 – k)) mod 32 = (23 +25) mod 32 = 48 mod 32 = 16 p

We received the word “cipher”, therefore the encryption was performed correctly.

Permutation cipher with key– is one of the many types of permutation ciphers (symbols of the original message are rearranged according to certain laws).

For a permutation with a key, a key is chosen - any word. The key symbols are numbered in the order they appear in the alphabet. A table is built in which the number of columns is equal to the number of letters in the key. The source text, along with spaces and punctuation marks, is recorded in this table. If last deadline is not completely filled, any characters (“blanks”) are written to the end of the line. Then the text is rewritten in columns, taking into account their numbering according to the key.

Example.

Let's choose the word " information" Let's number the key (the first of those in the key is the letter A in the alphabet, therefore it is assigned the number 1; the next letter in the alphabet is I, therefore the first letter I will have the number 2, and the second - 3; then comes the letter M, we assign it the number 4 etc.):

Let's encrypt the proverb: You will learn from the smart, and you will unlearn from the stupid.

Let's write it in the table under the key. The remaining cells to the end of the line are filled with “blanks”.

We rewrite the columns, taking into account their number:

Ouchdon osoyaoshzhnshlugtao yauch abmigzv utragspie, gz

For decryption, the ciphertext is written into a table in columns, taking into account their number.

The order of work.

Write down the resulting closed text (column S 1) in your notebook.

Questions.

What kind of text is called open text?

What text is called closed?

What is a key?

How is the encryption process carried out in the Caesar method?

What is "permutation encryption"?

How does the REST function work?

What does the VLOOKUP function do?

Applications:

Caesar's method

(tasks with answers for the teacher)

Key -> 8

Line:

Disguise is cunning and dexterity

Encrypted text:

Key -> 6

Line:

He who wants to know a lot needs little sleep

Encrypted text:

Key -> 4

Line:

Warning in time is the business of friends

Encrypted text:

Key -> 6

Line:

If the people come, the lake will overflow

Encrypted text:

Key -> 7

Line:

You can't go around the whole field with one horse

Encrypted text:

Key -> 9

Line:

Where words are rare, there they have weight

Encrypted text:

Key -> 10

Line:

The tongue is small, but it controls the whole body

Encrypted text:

Key -> 7

Line:

The more science, the smarter the hands

Encrypted text:

Key -> 9

Line:

It’s not enough to have a diploma, you need to understand the matter

Encrypted text:

Key -> 4

Line:

Wisdom is the least heavy burden on the journey

Encrypted text:

Key -> 10

Line:

Walking days are akin to theft

Encrypted text:

Key -> 5

Line:

The eyes are of little use if the mind is blind

Encrypted text:

Key -> 6

Line:

Whoever finds work a burden doesn’t know

Encrypted text:

Key -> 7

Line:

A good upbringing is the best inheritance

Encrypted text:

Key -> 8

Line:

Wave your scythe - there will be sweet peace

Encrypted text:

Key -> 9

Line:

He who starts a lot finishes little

Encrypted text:

Task cards

fischtrshtskti - ejts ershtsschad r schkhtshtskti

rshf yfelsh tufyf nuzhshv, shftshch uzhkf tjsf chkhzhshv

ufyichufyimtsa zhtjfyrg - ippt ifchline

Using key 6, decrypt information encrypted using the Caesar method:

ifnvtlshche uzhtsfk - fnltsf hlclsvlsh

hlfpu skhfmu yshm tskhtm fm hibmlmyag

mno yfchly shonus, yykh chtss lo skhozy

tskkh ysef, ok mypts bphshts mkhkopp

Using key 7, decrypt information encrypted using the Caesar method:

yumu ichtgyam fzsp, schmu ufmm chasp

Using key 9, decrypt information encrypted using the Caesar method:

hyfch nshfchh shoye, tsynch nofch schyrhoye

Using key 4, decrypt information encrypted using the Caesar method:

rchiftkhtsa - sdmrysadg tsgkypdg std w uchtsm

Using key 10, decrypt information encrypted using the Caesar method:

shshshnekhzhchep ocht mshashmyme yshocht

Using key 5, decrypt information encrypted using the Caesar method:

uch irem churpsh seru, ktsrn shs tsrkf

Using key 6, decrypt information encrypted using the Caesar method:

rftsch tszhzfshzh and sheifchshv, shftshch st Ilkftzh

Using key 7, decrypt information encrypted using the Caesar method:

ykhchhyamm ykhshtspschzfpm - tyyuyamm fzshtmlshschykh

Using key 8, decrypt information encrypted using the Caesar method:

chtsfieinad ttschtss - yimn schuimtt chttss

Using key 9, decrypt information encrypted using the Caesar method:

uych khtschmch cyascyoy, ychy hyfch uchtsayoy

The lesson is dedicated to consolidating knowledge about what threats exist to information and how it can be protected. It also introduces the basic types of encryption and teaches how to encode and decode information.

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Computer science lesson notes.

10th grade Lesson number: 3

Teacher: Krylov R.V.

Topic: Practical work: “Data encryption”

Lesson objectives:

1. Educational: create conditions for the formation of ideas about data encryption.
2. Educational:

• In order to develop independent thinking, develop self-control skills and rational memorization.
• For development purposes positive emotions, promote the development of emotional responsiveness during the lesson.

1. Educational:

• to develop moral qualities in the classroom,
• instill effort, diligence and responsibility in the classroom,
• develop the ability to work in a team.

1. Motivational:

• Arouse interest in the subject being studied;
• Arouse interest in healthy image life.

Lesson objectives:

1. Educational -

• consolidate the knowledge acquired in the previous lesson;
• introduce students to the main types of encryption;
• develop skills in encoding and decoding information;

1. Developmental –

• develop the skills of self-control and self-assessment of one’s knowledge, skills and abilities;
• develop oral and written speech;
• develop students' memory and logical thinking;
• develop skills to work with information technology.

1. Educational -

• cultivate moral qualities in the classroom,
• instill effort, diligence and responsibility in the classroom,
• develop the ability to work in a team.

Basic concepts:information protection, information security, types of threats, information security measures, cryptography, encoding and decoding of information.

Lesson type: combined lesson

Teaching methods:

1. Explanatory and illustrative verbal methods: story-introduction, story-exposition, conversation.
2. Explanatory and illustrative visual methods: demonstration method.
3. Reproductive method.

Forms of training: frontal, individual, group, pair work.

Equipment: personal computer, laptop, multimedia, handouts, printer, Microsoft Word, Microsoft PowerPoint,

Lesson plan:

stage	Lesson stage	Form of activity	Learning Tool	Purpose of using the product
	Organizing time	Frontal	Announcement of the beginning of the lesson	Attracting students' attention and getting them to work
	Setting lesson objectives for students	Frontal	Introductory story, Provoking dialogue	Development of logical thinking
	Testing knowledge and skills on the covered topic	Individual, group	Visual methods, role play	Identifying knowledge gaps and correcting them
	Health saving	Group work, conversation	Visual methods, Provocative dialogue
	Assimilation of initial knowledge	Frontal	Leading dialogue, conversation, narrative presentation, visual methods	Development of logical, algorithmic thinking
	Checking understanding	Individual	Work on encoding and decoding information	Identification of the quality and level of acquired knowledge, their correction.
	Summing up the lesson	Frontal	Dialogue	Analysis and assessment of achievement of the lesson goal, work prospects. Summing up the lesson, formulating conclusions. Encouraging children for their work in class, children’s self-assessment of their work in class

During the classes:

1. Organizational moment (checking students’ attendance and readiness for the lesson).
2. Announcing the topic and objectives of the lesson.

Teacher: Write down the topic of the lesson in your notebook:Solving problems on the topic: “Data encryption”

I chose the words as the epigraph of our lesson: “Who owns the information, owns the world.”(1 slide)

Whose words are these?

(Nathan Rothschild, an English banker who lived in the 19th century. This phrase became popular after it was quoted by British Prime Minister Winston Churchill.)

Teacher: Our tasks for today are to consolidate knowledge about what threats exist to information and how it can be protected. Get acquainted with the main types of encryption and learn how to encode and decode information.

1. Updating knowledge and checking the assimilation of the studied material.

Checking homework.

Teacher: Answer the following questions:

• What is information security?(2 slide)

(Information Security– this is the security of information from accidental and intentional actions that can cause unacceptable damage).

• What does the concept of Information Security include?

(Data protection– measures aimed at ensuring information security).

• What should information be protected from?

To answer this question we must rememberWhat types of threats to information exist?

(intentional (human actions) and accidental)

Do you have handouts on your desks? Annex 1 ). In your notebooks, you should write down intentional and accidental threats to information in two columns.

Teacher: Let's check the results of the work ( slide 3)

Deliberate threats	Random threats
malware (viruses, worms)	equipment failures
hacker attacks	software errors
sabotage	personnel errors
information espionage	illiteracy of users
falsification of information

Evaluation criteria: 0 errors – “5”

1 error – “4”

2-3 errors - “3”

The teacher records the results of his work

Teacher: We have discussed the types of threats. But how to protect information from these threats?

Very soon, you will graduate from school and plunge into big life with its joys and problems. Each of you will have to choose your own path in this life. Each of you will work in some organization.

Let's say that you and I work in two competing banks. What should you do as a bank administration to ensure information security?

You are given 2-3 minutes to come up with a set of measures to protect information in your bank ( appendix 2 ). Write them down on the form provided, and the manager will verbally explain your choice.

Procedural measures	Software and hardware measures	Administrative
personnel Management (separation of duties, minimum privileges)	login by password (smart card, fingerprints, etc.)	enterprise security policy
Access limitation ( security)	restriction of rights
power system protection	protocols work (login, access files, change settings, log out, etc.)
fire alarm	data encryption
defence from data interception	integrity control data
protection laptops and removable media	firewalls(firewalls)
prohibition to install foreignsoftware
backup data

Compare your results with the slide on the board and evaluate your work. The conclusion is summed up.

1. Health-saving.This is useful for everyone to know!

Teacher: Let's digress a little. Research by scientists has shown that constant work for

The computer increases the human body's need for many substances.

What do you think suffers more when working on a computer?

(Vision )

So, there is a special computer power supply. I suggest that you choose from the proposed products those that you think can be used in computer nutrition. And if possible, justify your choice.

Presentation "Computer nutrition"

Egg – contains vitamin A, which is part of the visual pigment; with a deficiency, “night blindness” develops (liver, whole milk),

Carrot – rich in provitamin A – carotene. Carrots are also rich in vitamins D, C, K and E

Cabbage – rich in vitamin K, which protects the retina of the eye,

Citrus – rich in vitamin C, very useful for the blood vessels of the eyes, makes them strong and elastic, prevents hemorrhages.

Tomatoes – contain lutein. Deficiency causes irreversible visual impairment

1. Assimilation of initial knowledge. Practical work on the computer with physical education.

Teacher: In the last lesson we talked about encryption.

What science deals with encryption methods?

(Cryptography)

What codes from human history do you know?

(Caesar cipher, German Enigma cipher machine)

• In the 19th century, mechanical encryption devices were actively developed - encryptors, which significantly facilitated and speeded up the processes of encryption and decryption. It was possible to teach how to use simple encryptors a large number of cryptographer operators who are far from understanding the essence of cryptographic science.

While working at the computer, children's attention is drawn to the visual simulator.

1. Checking understanding (practical work on the computer). Checking the results of practical work

Teacher: Now you will try to decode and encode some information.

Using a network environment from the teacher's machine, you will copy to your working directories from the folder“Data Encryption” presentation “Cryptography”.

The presentation contains 3 tasks.

You will formalize the answers to them in a WORD document with the name “Answer”, saving it in your directory.

Print the result.

Answers are checked from printed sheets on the slide in the presentation ( slide 4)

Students record their grades on a piece of paper.

Evaluation criteria (based on completed tasks): 3 – “5”

2 – “4”

13"

1. Summing up the lesson. Reflection (slide 4). Announcement of grades for lesson and homework

Students are asked to quickly answer three questions:

I found out today...

I realized today...

I learned today...

The scores are announced. Students decipher them using the standard Caesar cipher.(slide 5)

D/s: outline, tasks

Annex 1

Appendix 2

Procedural measures	Software and hardware measures	Administrative

Option 1.

Exercise 1.

Caesar's cipher. This cipher implements the following text transformation: each letter

source text is replaced by the next letter after it in the alphabet, which is considered

written in a circle. Using this cipher, encrypt the words: The bird is red with feathers,

and man is knowledge.

Task 2.

Using the Caesar cipher, decode the following phrases: IOBOYO – RPMPGYOB FNYA.

Task 3.

Use the word SUMMER as a keyword, code the words:

COMPUTER SCIENCE, SCHOOL.

Task 4.

The words MSTSYUEOYOSCH, YUCHOYCHYO were obtained using the Vigenère cipher with the keyword SUMMER. Restore the original words.

Task 5.

Dvtcnt ntcyj, f dhjpm crexyj.

Task 6.

Better a smart enemy than a stupid friend.

Task 7.

ROPEFTL, AKSREN Task 8.

Encode the words: Stupa, city, park.

Task 9.

B C D D F Z K L M N Sh Sh Ch C X F T S R P When encoding words, the consonants were mutually replaced, and the remaining letters and symbols remained in their places without change.

Code the phrases:

A) Hints and reproaches are family vices.

B) Where there is love and advice, there is no grief.

Practical work No. 1. Data encryption.

Option 2.

Exercise 1.

Caesar's cipher. This cipher implements the following text transformation: each letter of the original text is replaced by the next letter after it in the alphabet, which is considered to be written in a circle. Using this cipher, encrypt the words: The world is illuminated by the sun, and man is illuminated by knowledge.

Task 2.

Using the Caesar cipher, decode the following phrases: IOBOYO USFEPN EPVGBYUTA.

Task 3.

Vigenère cipher. This cipher is a Caesar cipher with a variable shift value.

The shift amount is specified using a keyword. For example, the keyword BEDA means the following sequence of letter shifts in the source text: 26512561, etc.

Use the word VASE as a keyword, code the words:

COMPUTER SCIENCE, SCHOOL.

Task 4.

The words LOEPUNICHLA, TSUSMLUI are obtained using the Vigenère cipher with the keyword VASE. Restore the original words.

Task 5.

Use as a clue: the arrangement of letters on a computer keyboard, decode the message:

Lj, hjt, hfncndj, vbktt, jufncndf.

Task 6.

Use as a key: the arrangement of letters on the computer keyboard, encode the message:

If you don’t have a friend, look for him, but if you find him, take care of him.

Task 7.

"Permutation" code. Coding is carried out by rearranging letters in a word according to the same general rule.

Restore the words and determine the permutation rule:

PSINLOETIL, ECHUINBK

Task 8.

Atbash code. Some fragments of biblical texts are encrypted using a cipher called Atbash. The encryption rule was to replace i-th letter alphabet with a letter with number n – i + 1, where n is the number of letters in the alphabet (which means the first letter is replaced by the last, the second by the penultimate, etc.).

Code the words: Arch, wig, king.

Task 9.

Gibberish letter. The encryption method is as follows: all consonant letters of the Russian alphabet are written in two rows; one half of the letters is at the top, the other half is at the bottom, and in reverse order(one letter under another).

–  –  –

Exercise 1.

Caesar's cipher. This cipher implements the following text transformation: each letter of the original text is replaced by the next letter after it in the alphabet, which is considered to be written in a circle. Using this cipher, encrypt the words: Knowledge and wisdom adorn a person.

Task 2.

Using the Caesar cipher, decode the following phrases: IOBOYO EYOMP OZYGOPE.

Task 3.

Vigenère cipher. This cipher is a Caesar cipher with a variable shift value.

The shift amount is specified using a keyword. For example, the keyword VAZA means the following sequence of letter shifts in the source text: 31913191, etc.

Use the word WINTER as a keyword, code the words:

COMPUTER SCIENCE, SCHOOL.

Task 4.

The words SH'DSHCHYNI, MYNKKOYU were obtained using the Vigenère cipher with the keyword WINTER. Restore the original words.

Task 5.

Use as a clue: the arrangement of letters on a computer keyboard, decode the message:

Pyfrjvs[ vyjuj, f lheptq vfkj.

Task 6.

Use as a key: the arrangement of letters on the computer keyboard, encode the message:

Die yourself, but help your comrade.

Task 7.

"Permutation" code. Coding is carried out by rearranging letters in a word according to the same general rule.

Restore the words and determine the permutation rule:

FNIMROITAAK, NOMOTIR

Task 8.

Atbash code. Some fragments of biblical texts are encrypted using a cipher called Atbash. The encryption rule was replacing i-th letters of the alphabet with a letter with number n – i + 1, where n is the number of letters in the alphabet (which means the first letter is replaced by the last, the second by the penultimate, etc.).

Encode the words: School, desk, milk.

Task 9.

Gibberish letter. The encryption method is as follows: all consonant letters of the Russian alphabet are written in two rows; one half of the letters is at the top, the other half is at the bottom, and in reverse order (one letter below the other).

–  –  –

Exercise 1.

Caesar's cipher. This cipher implements the following text transformation: each letter of the original text is replaced by the next letter after it in the alphabet, which is considered to be written in a circle. Using this cipher, encrypt the words: Be proud not of knowing the tops, but of knowing the roots.

Task 2.

Using the Caesar cipher, decode the following phrases: JOBOIA ABOUT RMYSHY OYE EBGAU.

Task 3.

Vigenère cipher. This cipher is a Caesar cipher with a variable shift value.

The shift amount is specified using a keyword. For example, the keyword VAZA means the following sequence of letter shifts in the source text: 31913191, etc.

Use the word ROSE as a keyword, code the words:

COMPUTER SCIENCE, SCHOOL.

Task 4.

The words KHAIKUFSHCH, ЪБШПЭЭСУЦ all are obtained using the Vigenère cipher with the keyword ROSE. Restore the original words.

Task 5.

Use as a clue: the arrangement of letters on a computer keyboard, decode the message:

Ytdthysq lheu – jgfcysq dhfu.

Task 6.

Use as a key: the arrangement of letters on the computer keyboard, encode the message:

Not into service, but into friendship.

Task 7.

"Permutation" code. Coding is carried out by rearranging letters in a word according to the same general rule.

Restore the words and determine the permutation rule:

IRPETNR, MOKYUPRET

Task 8.

Atbash code. Some fragments of biblical texts are encrypted using a cipher called Atbash. The encryption rule consisted of replacing the i-th letter of the alphabet with a letter with number n – i + 1, where n is the number of letters in the alphabet (meaning, the first letter is replaced by the last, the second by the penultimate, etc.).

Encode the words: Window, museum, threshold.

Task 9.

Gibberish letter. The encryption method is as follows: all consonant letters of the Russian alphabet are written in two rows; one half of the letters is at the top, the other half is at the bottom, and in reverse order (one letter below the other).

–  –  –

Code the phrases:

A) It is better to eat bread with water than to live with an evil wife.