In this article we will consider the Vigenère table for the Russian alphabet, namely its significance in development. Let's get acquainted with the terminology, historical facts. We will study decryption and its methods, as well as much more, which will ultimately allow us to clearly define the concept of the Vigenère table.
Introduction
There is a concept of "information encryption" - it is a certain mechanism for interpreting information into another form, which can only be recognized by knowing the way it is decrypted.
The Vigenère cipher is one such method of polyalphabetic encryption of information by making changes in the literal text that can only be read by knowing the keys. This polyalphabetic substitution was not invented all at once. The first scientist to describe this method was J. Battista Bellaso. He did this in the pages of the book La cifra del. Sig. in 1553, however, the method was named after B. Vigenère, a diplomat from France. Its methodology is quite simple to understand and execute. It is also inaccessible to ordinarycryptanalysis tools.
Historical data
L. Alberti, a well-known specialist in the fields of architecture and philosophy, in 1466 provided for inspection and evaluation a treatise that contained information on encryption, he was sent to the office of the Pope. The information told about different ways to perform this action. The final result of the work was presented by him in a method of encoding data that he personally developed, which he called "a cipher worthy of kings." This encryption mechanism was a polyalphabetic structure that formed an encryption disk. The invention of the printing press in Germany in 1518 gave new space for the development of cryptography.
In 1553, another step was taken to allow this area of human activity to develop. This was done by J. Bellazo. He called his work "The Cipher of Signor Bellaso". Here, a phrase or one word was used as a key, which served as a password. In the future, these ideas were transformed by Bellaso's compatriot, namely J. B. Porta. The main change was the proposal to abandon the standard alphabetical order in the first table row and, therefore, the transition to an order taken from arbitrary topics that can be used as the key needed for decryption. In accordance with the lessons of cryptography, the rows of the tables retained the same cyclic shifts. The book "On Secret Correspondence" published by Porta included information about the bigram cipher.
Mid 16th century,Italy. Here appeared a book edition of the work of G. Cardano, aimed at reflecting innovation in cryptographic ideas. For example, the concept of the “Cardano lattice” appeared.
After Blaise got acquainted with the works of Bellazo, Cardano and other thinkers, he also became interested in cryptographic work. In the future, he created the Vigenère cipher. Another significant work of his was the writing of a treatise on ciphers. In it, the author tried to lay out the basics of cybernetic cryptography.
Reviews about the cipher
The Vigenère table and the data encoding methods that followed from its use were extremely resistant to "manual" type cracking. The mathematician and writer L. Carroll awarded this cipher system the title of "unbreakable", which he expressed in an article on the "Alphabetic cipher" published in 1868
59 years later, one of the American magazines spoke about Vigenère's method of polyalphabetic encryption of literal text, just like Carroll had previously. However, in the 19th century, the Kasiska method was invented, which made it possible to refute these claims by breaking the cipher system.
Gilbert Vernam made an attempt to improve the broken cipher, but even taking into account its improvement, he remained unstable to cryptanalysis. In the future, Vernam himself has actually created a system that cannot be decoded.
General information
The Vigenère table for the English alphabet had many different forms of interpretation inways of operation. For example, the Caesar cipher assumed the presence of an alphabetical shift by a certain number of positions. For example, shifting by three letters would mean that the letter A would become D and B would become E. The cipher created by Vigenère is formed from a series of successive Caesar cipher systems. Here, any shift can have a different meaning. The encoding process may involve the use of special alphabetic tablets or Vigenère squares (tables). Twenty-six characters were created for the Latin alphabet, and any subsequent line in them was shifted by a certain number of positions. The symbol of the word that serves as a key determines the choice of the alphabet used.
Decryption
With the help of Vigenère encryption, the general characteristics of the frequency of character repetition in the source are "blurred". However, there remain features whose appearance in the text is regularly reproduced. The main weakness of this encoding is the repetition of keys. This allows you to build a cryptanalysis process consisting of two stages:
- Determine the password length. This is done by analyzing the distribution frequency of various text decimations. In other words, they take a source with a cipher in which every second letter is part of the code, then use the third, and so on. as a key.
- The use of cryptanalysis tools, which is the totalCaesar ciphers, which can be easily broken by considering them separately from each other.
Length is determined using the Kasiska and Friedman tests.
Kasiska Method
The first person who could develop an algorithm for breaking the Vigenère encryption method was C. Babbage. As an incentive, he used information received during an exchange of letters with J. Thwaites, where he claimed that he was able to develop a new encoding system. Charles Babbage proved the opposite to his interlocutor by reducing him to a particular case of Vigenère's work. Tweiss then advised Charles to hack the source. The decoding of the text concealed the words of A. Tennyson's poem, and the key word was the name of his wife, Emily. The publication of the discovery did not take place at the request of the cracker himself. The same algorithm was discovered by a Prussian army officer, Friedrich Wilhelm Kasiska, after whom it is named.
The idea is based on the periodic key flow technique. The natural form of the language also contains letter combinations that can be frequently repeated and are called bigrams and trigrams. Their frequency of repetition allows a chance to appear that will help determine the decryption key. The distance between the repetition of certain structures should correspond to the multiplicity of the length of the slogan. By calculating the longest total duration of each such distance, a working hypothesis for the key length can be obtained.
Kappa test
Another way to decryptThe Vigenère table and the encoding resulting from it can be considered a test created by V. Fridman. This method was developed in 1920. Here the concept of a match index was used, which could measure the frequency of repetition of specific characters, which would allow breaking the cipher system. Having information that randomly selected characters can match with a chance of approximately equal to 0.067% (for English), it is possible to determine the probability of their matching in the text. This allows you to create an estimate of the key length.
Frequency analysis
After you can determine the size of the key length, you can start fitting text into various columns in which they will correspond to some key character. All columns are formed thanks to the original text, encoded using the Caesar cipher. And the key to this method of coding is one speech unit for the Vigenère system. Using tools that allow breaking Caesar ciphers, we will thereby complete the complete decryption of the text.
An improved form of the Kasiska test, known as the Kirchhoff method, is based on comparing the occurrence of frequencies with certain symbols in each column. Thanks to them, the frequency of repetition of a character in the source texts is compared. How to use the Vigenère table, knowing all the symbols of the keys, it becomes clear to the cryptanalyst and it will not be difficult to read it in the final decryption process. The means of the Kirchhoff method are not applicable in cases where the given lattice of letters is scrambled. That is, there is a departure from the standard sequenceletters in the alphabet. However, it is important to know that the match test is still comparable to the Kasiska method, and therefore they can be used to determine the length of keys for special cases.
Variability
The alphabet system can be based on many other squares, of which there are quite a few, and they are easy to remember. Applicable on a par with the Vigenère square. Well-known analogies include a square named after Admiral F. Buford. It represents the rows of the Vigenère table, but pointing backwards. Sir Francis Beaufort was the man who created the scale for determining the speed of wind currents.
Summing up
An example of a Vigenère table can be seen in the figure below.
With general data on this encryption method, its history, development and relationship with various scientists, decryption methods, advantages and disadvantages, we can now clearly define this concept as a special way to transform information from one form to another with the aim of hiding the original data from a certain number of persons. The ability to encode messages has been an important strategic ingredient in all human wars.
