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Ancient methods of encryption.

Today I would like to talk about some of the old methods of encryption. About how our ancestors hid the messages from unnecessary eyes.

1. The Atbash

Apart from the ancient Egyptian hieroglyphs, which are considered to be the oldest method of cryptography (the science of methods for securing confidentiality and data integrity), atbash is one of the first methods of encryption. It is a simple substitution cipher for an alphabetic letter. The encryption rule consists in replacing the i-th letter of the alphabet with the letter n-i + 1, where n is the number of letters in the alphabet. Below are examples for the Latin, Russian and Hebrew alphabets:

Easy to use, but also easy to decrypt.

2. Skitala

Skitala, also known as the “cipher of ancient Sparta,” is also one of the oldest known cryptographic devices.

It is undeniably known that the wanderer was used in the war of Sparta against Athens at the end of the 5th century BC. e. It is also possible that it is mentioned by the poets Archilochus (VII century BC) and Pindar, although it is more likely that in their verses the word “wandered” was used in its primary meaning “staff”.

The principle of its action was laid down by Apollonius of Rhodes (middle of the 3rd century BC) and Plutarch (about 45-125 AD), but only the description of the latter was preserved.

Skitala was a long rod, on which a tape of parchment was wound (or two absolutely identical sticks (one was given to the commander, the second remained with the Council) with a winding bark). The tape was applied to the text along the axis of the skital, so that after unrolling the text became unreadable. To restore it, I needed to wander the same diameter.

It is believed that the author of the method of hacking the cipher is the wanderer, Aristotle, who wound the tape on a cone-shaped stick until readable pieces of text appeared.

It’s also a so-so method.

And now I will tell a little about the most talented military commander and inventor of ciphers.

Aeneas Tactician was one of the earliest Greek authors who wrote about the art of war. Apparently he was a politician and commander of the Arcadia Union. Coming from Stymphal.

Aeneas Tactician

According to Elian Tactics and Polybius, he wrote many treatises (Latin Hypomnemata) on this topic. The only surviving until now “How to survive in the siege” (Greek Περὶ τοῦ πῶς χρὴ). The work is mainly valuable by a large number of historical illustrations. Also, the work contains a description of the “book cipher”

transfer of information with the help of low-note marks in the text of the book or document, for example, needle holes placed next to the letters, which together form the original text of the secret message.

This method is not encryption and refers to steganography (a way of transferring or storing information taking into account the secret of the fact of such transmission or storage).

3. The Aeneas disk

The cryptographic tool for information protection, invented by Aeneas Tactician in the IV century BC. e. The device was a disk 13-15 cm in diameter and 1-2 cm thick with holes in it, the number of which was equal to the number of letters in the alphabet. Each hole was associated with a specific letter. In the center of the disc was a coil with a thread wound on it.

The encryption mechanism was very simple. In order to encrypt the message, it was necessary to alternately stretch the free end of the thread through the holes denoting the letters of the original unencrypted message. As a result, the disc itself, with thread threaded into its holes, was an encrypted message.

The recipient of the message consistently pulled the thread from each hole, thereby obtaining a sequence of letters. But this sequence was inverse to the original message, that is, he read the message backwards. Let’s assume the original message was “Αινειας” (Aeneas), then after deciphering the recipient saw “ςαιενια” before him. To read the received message, it was required to simply read from the end.

This type of information security had one significant drawback. The encrypted message was available for reading to anyone who could get hold of the disk (if, of course, he understood what it was, and not what a piece of wood with threads). Since the message was betrayed by ordinary messengers, not warriors, Eney provided for the possibility of rapid destruction of the transmitted information. To do this, it was enough to pull the entire thread at one of its ends, or to break the disk, just stepping on it. Usually it broke at the places of the encryption holes, as a result the thread that was threaded in them was tangled and it was impossible to read the message.

4. Ruler of Aeneas

For God’s sake, forgive for the image, but I did not find it better!

The original replacement code, based on the idea of ​​Aeneas. It is an improved form of the disk, which, as we saw, caused little confidence. One of the first truly cryptographic tools used in the transmission of messages, which were of particular importance and should not have been read by outsiders.

In cryptography, the Aeneas ruler was a device having holes, the number of which was equal to the number of letters of the alphabet. Each hole was designated by its letter; The letters on the holes were arranged in an arbitrary order. To the ruler was attached a reel with a thread wound on it. There was a slot near the coil.

When encrypted, the thread extends through the initial slot, and then twists up to the opening corresponding to the first letter of the encrypted text, while a string is tied to the thread at the point of its passage through the hole; then the thread returned to the slot and the entire text was encrypted in the same way. After the end of encryption, the thread was extracted and sent to the recipient of the message.

The recipient having an identical ruler, pulled the thread through the slot to the holes defined by the nodes, and restored the original text to the letters of the holes. Such a cipher is one example of a replacement cipher: when letters are replaced by the distance between nodules, taking into account the passage through the slot.

The key of the cipher was the order of the letters on the holes in the ruler. An outsider who received a thread (even with a ruler, but without letters written on it, which could be scattered), will not be able to read the message.

Without a ruler and awareness of the arrangement of letters, it is almost impossible to recreate the original message. In addition, in case of captivity, the thread with the message is easily destroyed. Unlike it, the method of Encryption by Aeneas disk assumes the transmission of both the cipher text and the key to it, which greatly simplifies the decoding of the message.

Since at the time of Aeneas no cryptanalysis tactic existed, the encryption technique with the Aeneas ruler was the first cryptographic tool not to be hacked.

It is worth mentioning that similar knotty letters were not intended to conceal information, but served as a writing for ancient peoples.

5. The Polybius Square

Or the chessboard Polybius is the original code for a simple substitution, one of the oldest coding systems proposed by Polybius (Greek historian, commander, statesman, 3rd century BC). This type of coding was originally used for the Greek alphabet, but then it was extended to other languages.

Despite the fact that the square was originally created for encoding, it can be successfully encrypted with it. In order to encrypt the text with a Polybius square, you need to take several steps:

Step 1: Generating an Encryption Table

Each language is separately compiled by an encryption table with the same (not necessarily) number of numbered rows and columns whose parameters depend on its capacity (the number of letters in the alphabet). We take two integers, the product of which is closest to the number of letters in the language – we get the required number of rows and columns. Then we inscribe in the table all the letters of the alphabet in a row – one in each cell. With a shortage of cells, you can write in one two letters (rarely used or similar in use).

Step 2: The principle of encryption

Method 1

We encrypt the word “SOMETEXT”:

For encryption on the square found the letter of the text and inserted into the encryption of the bottom of it in the same column. If the letter was on the bottom line, then take the top of the same column.

Method 2

The message is converted to coordinates by the Polybius square, coordinates are written vertically:

Method 3

The complicated version, which consists in the following: the received primary ciphertext is encrypted for a second time. At the same time, it is issued without splitting into pairs:

3425453443314154 

The resulting sequence of digits is shifted cyclically to the left by one step (an odd number of steps):

4254534433141543

This sequence is again divided into groups of two:

42 54 53 44 33 14 15 43

and the table is replaced by the final ciphertext:

At first glance, the cipher seems to be very unstable, but for its real evaluation it is necessary to take into account two factors:

-possibility to fill the Polybius square with letters arbitrarily, and not only strictly in alphabetical order;

-the ability to periodically replace squares.

Then the analysis of previous messages does not give anything, since by the time the cipher opens, it can be replaced.

Letters can fit into the table in any order – filling the table in this case is the key. For the Latin alphabet, one of 25 letters can be written in the first cell, the second one one of 24, the third one of 23, etc. We get the maximum number of keys for the cipher on the table of the Latin alphabet:

N = 25 * 24 * 23 * … * 2 * 1 = … em … prefigilion options (for the Russian even more, and only for the Chinese …)

Accordingly, the decryption of the message requires not only knowledge of the alphabet, but also the key with which the encryption table was compiled. But the arbitrary order of letters is hard to remember, so the user of the cipher must always have a key with him – a square. There is a danger of secret familiarization with the key of unauthorized persons. As a compromise solution was proposed key – password. The password is written without repeating the letters in a square; in the remaining cells in alphabetical order are written letters of the alphabet, which are absent in the password.

However, for the current techniques of cryptanalysis, the cipher is relatively simple and the easier it is, the longer the text. The most famous example of the instability of such a cipher is the story of Arthur Conan Doyle “Dancing Men”.

6. The Code of Caesar

Also known as a shift cipher, Caesar’s code or Caesar’s shift is one of the simplest and most widely known encryption methods.

The Caesar cipher is a kind of substitution cipher in which each character in plain text is replaced by a symbol that is on some constant number of positions to the left or to the right of it in the alphabet. For example, in a cipher with a shift to the right by 3, A would be replaced by F, B would be D, and so on.

The code is named in honor of the Roman emperor Guy Julius Caesar, who used it for secret correspondence with his generals.

Like all mono-alphabetic ciphers, Caesar’s cipher is easily hacked and has almost no application in practice.

7. The Cardano Grating

Text of the note:

Sir John appreciates you and again repeats that everything that is available to him, now yours, forever. Can he deserve forgiveness for his former delays through his charm.

Encrypted message:

In May, Spain will send its ships to war.

The encryption and decryption tool, which is a special rectangular (in a particular case – a square) table-card, some of whose cells are cut out.

In 1550, Gerolamo Cardano (1501-1576) proposed a simple grid for encrypting messages. He planned to mask messages under the usual message, so that in general they were not completely similar to encrypted messages. Such a disguised message is considered an example of steganography.

It is known that Cardinal Richelieu (1585-1642) was an adherent of Cardano’s lattice and used it in personal and business correspondence. Educated Europeans of the XVII century were familiar with the play of words in literature, including acrostic, anagram and ciphers.

The grid contains holes for individual symbols, and the message is filled with a set of letters or numbers and is obviously a cryptogram, while Cardano intended to make a steganogram.

One of the varieties of the Cardano grid is a rotating grid or grid, which is based on a chessboard that was used at the end of the 16th century. The rotating grid again appeared in a more complex form at the end of the XIX century, but by this time any connection with Cardano remained only in the title.

When the encrypted Cardano grating of an arbitrary form is poorly composed, it is distinguished by an unnatural language and an ever-changing style. A specialist can try to restore the grid if he has several copies of suspicious messages from the correspondence. When the message is encrypted well, it is difficult to identify. Even if the expert considers the message suspicious, the encrypted text can contain any innocent letter. Therefore, in practice, the only solution is to get the grid itself.

To read the encrypted message, it is necessary to put Cardano’s grille on the text the required number of times and read the letters located in the cut out cells.

The method is slow and in the case of encryption by an array of arbitrary shape requires the availability of literary skills. But most importantly, any encryption device can be lost, stolen or confiscated. Thus, to lose one lattice means to lose all secret correspondence, which was encrypted with the help of this grating.

The Cardano grating in its original form is more a source of literary than cryptographic interest. For example, the Voynich manuscript , which could be a fake encryption of the 16th century, probably was built using the Cardano grid used to compose a pseudo-random nonsense from a pre-existing text.

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