Once upon a time, the eldest Nastya and I voraciously played detectives and detectives, came up with our own codes and methods of investigation. Then this hobby passed and now it has returned again. Nastya has a fiancé, Dimka, who enthusiastically plays scouts. My daughter shared his passion. As is known, in order to transmit to each other important information, intelligence officers need a code. With these games you will also learn how to encrypt a word or even an entire text!

White spots

Any text, even without a code, can turn into hard-to-read gibberish if the spaces between letters and words are incorrectly placed.

For example, this is what a simple and understandable sentence turns into "Meet me at the lakeside" - "Meeting Yanaber Yeguozera".

Even an attentive person will not immediately notice the catch. But experienced intelligence officer Dimka says that this is the simplest type of encryption.

No vowels

Or you can use this method - write the text without vowels.

As an example, here is a sentence: "The note lies in the hollow of an oak tree that stands at the edge of the forest". The ciphertext looks like this: "Zpska lies in dpl db, ktr stt n pshke ls".

This will require ingenuity, perseverance, and, possibly, the help of adults (who also sometimes need to exercise their memory and remember their childhood).

Read it backwards

This encryption combines two methods at once. The text must be read from right to left (that is, vice versa), and spaces between words can be placed at random.

Here, read and decipher: "Neleta minv oak, manoro tsop irtoms".

Second for the first

Or each letter of the alphabet can be represented by the letter that follows it. That is, instead of “a” we write “b”, instead of “b” we write “c”, instead of “c” we write “d” and so on.

Based on this principle, you can create an unusual cipher. To avoid confusion, we made mini-cheat sheets for all participants in the game. It is much more convenient to use this method with them.

Guess what kind of phrase we have encrypted for you: "Tjilb g tjsibmzh fiobue mzhdlp – po ozhlpdeb ozh toynbzhu shmarf".

Deputies

The "Replacement" method is used on the same principle as the previous cipher. I read that it was used to encrypt sacred Jewish texts.

Instead of the first letter of the alphabet, we write the last, instead of the second, the penultimate one, and so on. That is, instead of A - Z, instead of B - Yu, instead of C - E...

To make it easier to decipher the text, you need to have the alphabet and a piece of paper with a pen on hand. Look at the letter matches and write it down. It will be difficult for a child to estimate by eye and decipher.

Tables

You can encrypt text by first writing it into a table. You just need to agree in advance which letter you will use to mark the spaces between words.

A small hint - it should be a common letter (such as p, k, l, o), because letters that are rarely found in words immediately catch the eye and because of this the text is easily deciphered. You also need to discuss how big the table will be and how you will enter the words (from left to right or top to bottom).

Let's encrypt the phrase together using the table: At night we go to catch crucian carp.

We will denote a space with the letter “r”, writing words from top to bottom. Table 3 by 3 (we draw in the cells of a regular notebook sheet).

Here's what we get:
N B I M O T K A Y
O Y D R V A S R
CH R E L I R R E.

Lattice

In order to read the text encrypted in this way, you and your friend will need the same stencils: sheets of paper with squares cut out on them in random order.

The encryption must be written on a piece of paper in exactly the same format as the stencil. The letters are written in the hole cells (and you can also write, for example, from right to left or from top to bottom), the remaining cells are filled with any other letters.

The key is in the book

If in the previous code we prepared two stencils, now we will need identical books. I remember back in my childhood the boys at school used Dumas’s novel “The Three Musketeers” for these purposes.

The notes looked something like this:
"324 s, 4 a, b, 7 words.
150 s, 1 a, n, 11 sl...”

First digit indicated the page number,
second– paragraph number,
third letter– how to count paragraphs from above (v) or from below (n),
fourth letter- word.

In my example the right words need to search:
First word: on page 324, 4th paragraph from the top, seventh word.
Second word: on page 150, 1 paragraph from the bottom, eleventh word.

The decryption process is slow, but no outsider will be able to read the message.

My memories from childhood + imagination were enough for exactly one quest: a dozen tasks that are not duplicated.
But the children liked the fun, they asked for more quests and had to go online.
This article will not describe the script, legends, or design. But there will be 13 ciphers to encode the tasks for the quest.

Code number 1. Picture

A drawing or photo that directly indicates the place where the next clue is hidden, or a hint at it: broom + socket = vacuum cleaner
Complication: make a puzzle by cutting the photo into several parts.

Code 2. Leapfrog.

Swap the letters in the word: SOFA = NIDAV

Cipher 3. Greek alphabet.

Encode the message using the letters of the Greek alphabet, and give the children the key:

Code 4. Vice versa.

Write the assignment backwards:

• every word:
  Etishchi dalk extra Jonsos
• or an entire sentence, or even a paragraph:
  Etsem morkom momas v - akzaksdop yaaschuudelS. itup monrev an yv

Code 5. Mirror.

(when I did the quest for my children, at the very beginning I gave them " magic bag": there was a key to the "Greek alphabet", a mirror, "windows", pens and sheets of paper, and all sorts of unnecessary things for confusion. Finding the next riddle, they had to figure out for themselves what from the bag would help them find the answer)

Code 6. Rebus.

The word is encoded in pictures:

Cipher 7. Next letter.

We write a word, replacing all the letters in it with the following ones in alphabetical order (then I is replaced by A, in a circle). Or the previous ones, or the next ones after 5 letters :).

CABINET = SHLBH

Code 8. Classics to the rescue.

I took a poem (and told the children which one) and a code of 2 numbers: line number number of letters in the line.

Example:

Pushkin "Winter Evening"

The storm covers the sky with darkness,
Whirling snow whirlwinds;
Then, like a beast, she will howl,
Then he will cry like a child,
Then on the dilapidated roof
Suddenly the straw will rustle,
The way a belated traveler
There will be a knock on our window.

21 44 36 32 82 82 44 33 12 23 82 28

Did you read it, where is the hint? :)

Code 9. Dungeon.

Write the letters in a 3x3 grid:

Then the word WINDOW is encrypted like this:

Code 10. Labyrinth.

My children liked this code; it is unlike the others, because it is not so much for the brain, but for attention.

So:

On a long thread/rope you attach the letters in order, as they appear in the word. Then you stretch the rope, twist it and entangle it in every possible way between the supports (trees, legs, etc.). Having walked along the thread, as if through a maze, from the first letter to the last, the children will recognize the clue word.

Imagine if you wrap one of the adult guests in this way!
Children read - The next clue is on Uncle Vasya.
And they run to feel Uncle Vasya. Eh, if he is also afraid of tickles, then everyone will have fun!

Code 11. Invisible ink.

Use a wax candle to write the word. If you paint over the sheet with watercolors, you can read it.
(there are other invisible inks... milk, lemon, something else... But I only had a candle in my house :))

Code 12. Rubbish.

The vowels remain unchanged, but the consonants change according to the key.
For example:
SHEP SCHOMOZKO
reads as - VERY COLD, if you know the key:
D L X N H
Z M SCH K V

Code 13. Windows.

The kids loved it incredibly! They then used these windows to encrypt messages to each other all day long.
So: on one sheet of paper we cut out windows, as many as there are letters in the word. This is a stencil, we apply it to a blank sheet of paper and write a clue word in the windows. Then we remove the stencil and write many different unnecessary letters on the remaining blank space of the sheet. You can read the code if you attach a stencil with windows.
The children were at first stupefied when they found a sheet covered with letters. Then they twisted the stencil back and forth, but you still need to put it on the right side!

Code 14. Map, Billy!

Draw a map and mark (X) the location with the treasure.
When I did the quest for mine for the first time, I decided that the map was very simple for them, so I needed to make it more mysterious (then it turned out that just a map would be enough for the children to get confused and run in the opposite direction)...

This is the map of our street. Hints here are house numbers (to understand that this is actually our street) and huskies. This dog lives with a neighbor across the street.
The children did not immediately recognize the area and asked me leading questions..
Then 14 children took part in the quest, so I united them into 3 teams. They had 3 versions of this map and each one had its place marked. As a result, each team found one word:
"SHOW" "FAIRY TALE" "TURNIP"
This was the next task :). He left behind some hilarious photos!
For my son’s 9th birthday, I didn’t have time to invent a quest, so I bought it on the MasterFuns website.. At my own peril and risk, because the description there is not very good.
But my children and I liked it because:

1. inexpensive (similar to about 4 dollars per set)
2. quickly (paid - downloaded, printed - everything took 15-20 minutes)
3. There are a lot of tasks, with plenty to spare. And although I didn’t like all the riddles, there was plenty to choose from, and you could enter your own task
4. everything is decorated in the same monster style and this gives the holiday effect. In addition to the quest tasks themselves, the kit includes: a postcard, flags, table decorations, and invitations to guests. And it's all about monsters! :)
5. In addition to the 9-year-old birthday boy and his friends, I also have a 5-year-old daughter. The tasks were beyond her, but she and her friend also found entertainment - 2 games with monsters, which were also in the set. Phew, in the end - everyone is happy!

Ever since humanity grew to writing, codes and ciphers are used to protect messages. The Greeks and Egyptians used ciphers to protect personal correspondence. As a matter of fact, it is from this glorious tradition that grows modern tradition breaking codes and ciphers. Cryptanalysis studies codes and methods of breaking them, and this activity can bring a lot of benefits in modern realities. If you want to learn this, you can start by studying the most common ciphers and everything connected with them. In general, read this article!

Steps

Decryption of substitution ciphers

Start by looking for one-letter words. Most ciphers based on relatively simple substitution are most easily broken by simple brute-force substitution. Yes, you will have to tinker, but it will only get more difficult.

• Words consisting of one letter in Russian are pronouns and prepositions (ya, v, u, o, a). To find them, you will have to carefully study the text. Guess, check, fix or try new options - there is no other method of solving the cipher.
• You must learn to read the code. Hacking it is not that important. Learn to pick out the patterns and rules underlying the cipher, and then breaking it will not be fundamentally difficult for you.

1. Look for the most frequently used symbols and letters. For example, in English these are “e”, “t” and “a”. When working with a code, use your knowledge of language and sentence structure, based on which you make hypotheses and assumptions. Yes, you will rarely be 100% sure, but solving codes is a game where you are required to make guesses and correct your own mistakes!

   • Double characters and short words look first, try to start decoding with them. It’s easier, after all, to work with two letters than with 7-10.

2. Pay attention to apostrophes and symbols around. If the text contains apostrophes, then you are in luck! So, in case English language, the use of an apostrophe means that characters such as s, t, d, m, ll or re are encrypted after. Accordingly, if there are two identical characters after the apostrophe, then this is probably L!

   Try to determine what type of cipher you have. If you, when solving a code, certain moment If you understand which of the types described above it belongs to, then you have practically solved it. Of course, this will not happen very often, but the more codes you solve, the easier it will be for you later.

   • Digital substitution and keyboard ciphers are most common these days. When working on a cipher, first check to see if it is the same type.

   Recognition of common ciphers

   1. Substitution ciphers. Strictly speaking, substitution ciphers encode a message by replacing some letters with others, according to a predetermined algorithm. The algorithm is the key to solving the cipher; if you solve it, then decoding the message will not be a problem.

      • Even if the code contains numbers, Cyrillic or Latin, hieroglyphs or unusual characters - as long as the same types of characters are used, then you are probably working with a substitution cipher. Accordingly, you need to study the alphabet used and derive substitution rules from it.

   2. Square cipher. The simplest encryption, used by the ancient Greeks, based on the use of a table of numbers, each of which corresponds to a letter and from which words are subsequently composed. This is really simple code, kind of the basics. If you need to solve a cipher in the form of a long string of numbers, it is likely that the methods of working with a square cipher will be useful.

      Caesar's cipher. Caesar could not only do three things at once, he also understood encryption. Caesar created a good, simple, understandable and, at the same time, crack-resistant cipher, which was named in his honor. The Caesar Cipher is the first step towards learning complex codes and ciphers. The essence of the Caesar cipher is that all characters of the alphabet are shifted in one direction by a certain amount characters. For example, shifting 3 characters to the left will change A to D, B to E, etc.

      Watch out for keyboard patterns. Based on the traditional QWERTY keyboard layout, various ciphers are now being created that work on the principle of displacement and substitution. The letters are shifted left, right, up and down by a certain number of characters, which allows you to create a cipher. In the case of such ciphers, you need to know in which direction the characters were shifted.

      • So, by moving the columns up one position, “wikihow” becomes “28i8y92”.

      • Polyalphabetic ciphers. Simple substitution ciphers rely on the cipher creating a kind of alphabet for encryption. But already in the Middle Ages it became too unreliable, too easy to hack. Then cryptography took a step forward and became more complex, starting to use symbols from several alphabets for encryption. Needless to say, the reliability of encryption immediately increased.

   What does it mean to be a code breaker?

   Be patient. Breaking a code requires patience, patience and more patience. And perseverance, of course. It's slow painstaking work, associated with a large number disappointments due to common mistakes and the need to constantly select symbols, words, methods, etc. A good codebreaker simply has to be patient.

Despite the development of decryption technologies, the best minds planets continue to puzzle over unsolved messages. Below is a list of 10 ciphers whose contents have not yet been revealed.

1. The most important encrypted message ancient culture island of Crete became a clay product found in the city of Festus in 1903. Both sides are covered with hieroglyphs written in a spiral. Experts were able to distinguish 45 types of signs, but only a few of them were identified as hieroglyphs that were used in the pre-palatial period ancient history Krita.

2. Linear A was also found in Crete and named after British archaeologist Arthur Evans. In 1952, Michael Ventris deciphered Linear B, which was used to encrypt Mycenaean, the oldest known variant of Greek. But Linear A has only been partially solved, and the solved fragments are written in some kind of non-literate language. known to science a language not related to any known language.
(additional materials.)

3. Kryptos is a sculpture that American sculptor James Sanborn installed on the grounds of the CIA headquarters in Langley, Virginia, in 1990. The encrypted message written on it still cannot be deciphered.

4. Code printed on chinese gold bar. Seven gold bars were allegedly issued to General Wang in Shanghai in 1933. They contain pictures, Chinese writings and some encrypted messages, including in Latin letters. They may contain certificates of authenticity of the metal issued by one of the US banks. Content Chinese characters indicates that the value of gold bars exceeds $300 million.

5. - three encrypted messages, which are believed to contain information about the whereabouts of a treasure of two wagons of gold, silver and precious stones, buried in the 1820s near Lynchburg, in Bedford County, Virginia, by a party of gold miners led by Thomas Jefferson Bale. The price of the treasure, which has not been found until now, in terms of modern money, should be about 30 million dollars. The mystery of the cryptograms has not yet been solved; in particular, the question of the real existence of the treasure remains controversial. One of the messages has been deciphered - it describes the treasure itself and gives general indications of its location. The remaining undisclosed letters may contain the exact location of the bookmark and a list of owners of the treasure. ()

6. Voynich manuscript, which is often called the most mysterious book in the world. The manuscript uses a unique alphabet, has about 250 pages and includes drawings depicting unknown flowers, naked nymphs and astrological symbols. It first appeared at the end of the 16th century, when Holy Roman Emperor Rudolf II bought it in Prague from an unknown merchant for 600 ducats (about 3.5 kg of gold, today more than 50 thousand dollars). From Rudolph II the book passed to nobles and scientists, and at the end of the 17th century it disappeared. The manuscript reappeared around 1912, when it was purchased by the American bookseller Wilfrid Voynich. After his death, the manuscript was donated to Yale University. British scientist Gordon Wragg believes that the book is a clever hoax. The text contains features that are not characteristic of any language. On the other hand, some features, such as the length of words and the way letters and syllables are connected, are similar to those existing in real languages. "Many people think it's too complicated to be a hoax; it would take some mad alchemist years to build," says Rugg. However, Rugg shows that such complexity could be achieved easily by using a encryption device invented around 1550 called Cardan's reticle. In this symbol table, words are created by moving a card with holes cut in it. Thanks to the spaces left in the table, the words are obtained different lengths. By superimposing such lattices on the manuscript's syllable table, Rugg created a language that shares many, if not all, of the features of the manuscript's language. According to him, it would take three months to create the entire book. (, Wikipedia)

7. Dorabella Cipher, composed in 1897 by British composer Sir Edward William Elgar. He sent a letter in encrypted form to the city of Wolverhampton to his friend Dora Penny, the 22-year-old daughter of Alfred Penny, rector of St. Peter's Cathedral. This code remains unsolved.

8. Until recently, the list also included chaocipher, which could not be revealed during the lifetime of its creator. The cipher was invented by John F. Byrne in 1918, and for almost 40 years he unsuccessfully tried to interest the US authorities in it. The inventor offered a cash reward to anyone who could solve his code, but as a result, no one applied for it. But in May 2010, Byrne's family members handed over all his remaining documents to the National Cryptography Museum in Maryland, which led to the disclosure of the algorithm.

9. D'Agapeeff cipher. In 1939, British cartographer of Russian origin Alexander D'Agapeyeff published a book on the basics of cryptography, Codes and Ciphers, in the first edition of which he presented a cipher of his own invention. This cipher was not included in subsequent editions. Subsequently, D'Agapeyeff admitted that he had forgotten the algorithm for breaking this cipher They suspect that the failures that befell everyone who tried to decipher his work were caused by the fact that the author made mistakes when encrypting the text. But in our time, there is hope that the cipher can be broken using. modern methods- for example, a genetic algorithm.

10. Taman Shud. On December 1, 1948, the dead body of a man was found on the Australian coast at Somerton, near Adelaide, dressed in a sweater and coat, despite a typically hot day for the Australian climate. No documents were found on him. Attempts to compare the prints of his teeth and fingers with the available data on living people also led to nothing. A pathological examination revealed an unnatural rush of blood, which filled, in particular, his abdominal cavity, as well as an increase internal organs, but no foreign substances were found in his body. At the same time, a suitcase was found at the railway station that could have belonged to the deceased. The suitcase contained trousers with a secret pocket, in which they found a piece of paper torn from a book with words printed on it. Taman Shud. The investigation established that the piece of paper was torn from a very rare copy of the collection "Rubai" of the great Persian poet Omar Khayyam. The book itself was found in the back seat of a car, left unlocked. On the back cover of the book, five lines were carelessly scribbled in capital letters - the meaning of this message could not be deciphered. To this day, this story remains one of Australia's most mysterious mysteries.

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identify immutable parts. Looking ahead, we can cite as an example the Enigma cipher machine (see Chapter 9), which contained several wheels; there were wires inside these wheels; The wiring of the wires inside the wheels did not change, but the order of the wheels inside the car itself changed daily. Thus, the wiring of the wires was an unchangeable part, and the order of the wheels was a variable part. Hacking the system is the most time-consuming part of the job; it can last several weeks or even months and require the use of mathematical methods, the search for and use of operator errors, and even information obtained by spies.

Once all the immutable parts of the system have been determined, it is necessary to determine all the variable parts (such as the initial positions of the wheels in the Enigma cipher machine, which changed for each message). This is the task message key discovery. After solving it, the messages will be decrypted.

So, hacking refers to the encryption system as a whole, while opening the keys is associated with the decryption of individual messages.

Codes and ciphers

Although the words code and cipher are often used loosely, we will make a distinction between these concepts. In code, frequently occurring text elements (which may consist of one or more letters, numbers, or words) are usually replaced by four or five letters or numbers, called code groups and are taken from the code book. For particularly frequently used expressions or characters, the codebook may offer several code groups. This is done so that the cryptographer can vary them in order to complicate their identification. So, for example, in four-digit digital code for the word "Monday" there can be three alternative code groups - for example, 1538, or 2951, or 7392. We will look at the codes in Chapter 6.

Codes are a special case encryption systems, but not all encryption systems are codes . We will use word cipher in relation to encryption methods that use non-codebooks and the ciphertext is derived from the original plaintext according to a specific rule. Nowadays, instead of the word "rule" they prefer to use the word "algorithm", especially if we're talking about O computer program. The distinction between the concepts of code and cipher is sometimes not entirely clear, especially for simple systems. Perhaps we can consider that the Julius Caesar cipher uses a one-page code book, where each letter of the alphabet is associated with a letter that is three positions further in the alphabet. However, for most of the systems we'll look at, this distinction will be quite clear. For example, "Enigma", which is often

mistakenly called the "Enigma code", it is certainly not a code at all, but

cipher machine.

Historically, until relatively recently, cryptography was dominated by two basic ideas, and many encryption systems (including almost all of those described in the first eleven chapters of this book) were based on one or both of them. The first idea was to shuffle the letters of the alphabet (as one would normally shuffle a deck of cards) to produce what could be considered a random order, permutation, or anagram of the letters. The second idea is to convert the letters of the message into numbers (for example, by putting A=0, B=1, ..., Z=25), and then add to them (number by number) other numbers called gamma, which , in turn, can be letters converted to numbers. If the result of addition is a number greater than 25, subtract 26 from it (this method is called modulo addition 26). The result is then converted back

V letters. If the numbers added to the text are obtained using a rather difficult to predict process, then the message encrypted in this way is very difficult, or even impossible, to decipher without knowledge of the gamma.

It is interesting to note that the Julius Caesar cipher, however simple it may be, can be considered an example of both types. In the first case, our "shuffle of the deck" is equivalent to simply moving the last three cards to the beginning of the deck, so that all the letters are moved down three positions, and X, Y and Z are at the beginning. In the second case, the scale is the number 3, repeated an infinite number of times. It is impossible to imagine anything “weaker” than such a range.

Translation of a message into another language, perhaps, could also be considered a certain type encryption using a code book (that is, a dictionary), but this is still too loose a use of the word code. However, this method of translating into another language, when they climb after every word

V A dictionary like a code book is definitely not to be recommended. This is known to anyone who has tried to learn a foreign language.*) On the other hand, sometimes it is quite reasonable to use a little-known language to convey messages whose relevance is limited in time. They say, for example, that during the Second World War, American troops in Pacific Ocean soldiers from the Navajo Indian tribe were sometimes used as telephone operators to transmit

*) I remember how a certain schoolboy wrote an essay in French about how in the Middle Ages a traveler arrived at a hotel at night and knocked on the door. In response he hears "What Ho! Without." (“What the hell! Get out!” - approx. transl.). The student translated this expression into French verbatim, substituting the French words: "Que Ho! Sans." (it turned out “What the hell! Without.” - approx. transl.). Teacher French, having read this, was speechless for a moment, and then noticed; "You probably found these words in the dictionary they give out free with bags of sugar."

messages on your native language, quite reasonably assuming that even in the event of interception telephone conversations the enemy would hardly find in his ranks a person who speaks this language and is able to understand the content of the message.

Another way to hide the content of information is to use some kind of personal cursive. This method was used by authors back in the Middle Ages personal diaries- for example, Samuel Pepys. Such codes are not difficult to open if there are enough entries in the diary. Regular repetition of certain symbols (for example, signs indicating the days of the week) is a good help in reading certain words and expressions. An example of more thorough work would be the decipherment of the ancient Mycenaean writing system, known as Linear B, where the characters corresponded to the syllables of the ancient Greek language; the credit for deciphering this type of writing belongs to Michael Ventris*) (see).

Widespread computers and the ability to practically build complex electronic circuits on silicon chips revolutionized both cryptography and cryptanalysis. As a result, some modern systems encryptions are based on advanced mathematical concepts and require a solid computing and electronic base. Therefore, in the pre-computer era it was almost impossible to use them. Some of them are described in chapters 12 and 13.

Assessing the strength of an encryption system

When a new encryption system is proposed, it is very important to evaluate its resistance to all already known attack methods in conditions where the cryptanalyst knows the type of encryption system used, but not in all details. The strength of an encryption system can be assessed for three different situations:

(1) the cryptanalyst knows only ciphertexts;

(2) the cryptanalyst knows the cipher texts and the original plaintexts to them;

(3) the cryptanalyst knows both ciphertexts and plaintexts, which he himself selected.

The first case reflects a “typical” situation: if under these conditions the encryption system can be broken in short time, then you should not use it. The second situation arises, for example, if identical messages are encrypted both new system, and according to the old one, which

*) Linear B is one of the most ancient systems of Greek writing. Found on clay tablets in Knossos (Crete) and Pylos. Deciphered by Michael Ventris (1922-1956), English architect and linguist (approx. transl.).

A cryptanalyst can read. Such situations related to cases serious violation information protection rules occur quite often. The third situation arises mainly when a cryptographer, wanting to evaluate the strength of the system he has created, invites his colleagues, playing the role of an adversary, to break his cipher and allows them to dictate encryption texts to him. This is one of the standard procedures testing new systems. Very interesting task for a cryptanalyst - compose texts in such a way that after encrypting them, obtain maximum information about the details of the system. The structure of these messages depends on how exactly the encryption is done. The second and third situations can also arise if the cryptanalyst has a spy in the cryptographer's organization: this is exactly what happened in the 30s of the last century, when Polish cryptanalysts received the plaintext and encrypted texts of messages encrypted on the German Enigma cipher machine. An encryption system that cannot be broken even in such a situation (3) is a truly strong cipher. This is exactly what the cryptographer strives for, and what the cryptanalyst fears.

Codes that detect and correct errors

Another class of codes is intended to provide error-free transmission information, and not to hide its content. Such codes are called detecting and correcting errors, they are the subject of large-scale mathematical research. These codes have been used since the earliest days of computers to protect against errors in memory and data recorded on magnetic tape. The earliest versions of these codes, such as Hamming codes, are able to detect and correct a single error in a six-bit character. A more recent example is the code that was used on spaceship"Mariner" for transmitting data from Mars. Designed to take into account the potential for significant signal distortion on its long journey to Earth, this code was capable of correcting up to seven errors in each 32-bit “word”. A simple example code of another level, detecting, but does not correct errors, is the ISBN (International Standard Book Number) code. It consists of ten characters (ten digits or nine digits with an X at the end, which indicates the number 10), and allows you to check for errors in the ISBN number. The check is performed as follows: calculate the amount

(first digit) 1+(second digit) 2+(third digit) 3+...+(tenth digit) 10.