Features of modern information transmission systems

At first glance, these concepts may seem synonymous, but they have completely different meanings.

Cipher is a method of converting information in order to protect it from unauthorized users. The science that studies these methods and methods of information encryption is called cryptography. It should be noted that historically in cryptography some purely military terms were fixed : the enemy, the attack, the cipher, etc. - they accurately reflect the meaning of the relevant concepts. At the same time, military terminology based on the term "code" has nothing to do with theoretical cryptography, because in recent decades the coding theory has been formed - a large scientific direction that develops and studies methods of protecting information from the occurrence of random errors on communication channels. Therefore, the saying "coding is a kind of encryption" is incorrect.

Coding and encryption are closely related, but each of these processes has its own goals. Coding information is carried out in order to turn information according to certain rules into a form convenient for transmission on a certain communication channel. The basis of any coding is the number system as a record of the mathematical structure, on the basis of which it is possible to obtain any number of different codes. As a rule, codes are represented by binary strings of zeros and ones (such a record is natural for use by computers when transferring and storing information).

Encryption of information is a way of transforming information to protect against unauthorized access. Thus, the message is encrypted so that it becomes incomprehensible, and encoded - in order to remain intelligible even after transmission through a communication channel, which can be affected by noise. Coding information should reduce the character text with a limited number of characters (ie, the coding should be optimal), as well as detecting and correcting errors in the transmission and storage of information (the coding should be corrective).

Therefore, if it is necessary to transfer information via a certain communication channel so that reliable reliable secret information is obtained at the output, it is necessary to combine both transformation processes, namely:

- Translate the message to a certain number system (sometimes it is enough to translate it into a binary number system , but there are others, for example, binomial, Fibonacci etc.);

- Encrypt the message (there are many different methods of encryption, because the creation of ciphers reaches the times of antiquity);

- The received encrypted message must be encoded so that the message at the output can be uniquely decoded;

- Decode the message, it must identify and correct the errors that occurred when the message was sent;

- Decrypt the message according to the encryption performed (the sender and the recipient must first agree on the encryption procedure for this). Typically, this procedure consists of a general method and a "key". The key is the collection of data that defines a particular transformation from the set of transformations of the cipher;

- The received message is transferred from the received system of calculation in initial.

Thus, the protection and the correct transmission of information require a lot of effort. In our time, powerful computing technology greatly simplifies this process, but not always with the help of technology it is possible to decrypt the message, especially if the key is unknown. In connection with obstacles in the communication channels, information can be distorted, therefore, such coding techniques are used that allow to identify and correct the error.

So, a message is sent over the communication channel. The received message is checked for the parity of the number of units: if the number of units is even, then we assume that there are no errors, and when decoding we reject the last digit. If the number of units is odd, the message is sent with errors. The disadvantage of this method is that it only allows to detect the error without correcting them, whereas the code with repetition not only detects, but also corrects errors.

So, each of the above coding methods has its drawbacks, but these methods play a big role in coding theory and underlie the construction of more perfect codes. Nowadays codes of Hamming, Nagoye, Reed-Muller, Hadamard, etc. are used.

Concerning the ciphers as a means of protecting information from unauthorized access, there are several ways in which you can classify ciphers. Usually the classification is considered as the main one:

A) restricted use ciphers;

B) general use ciphers with public key;

C) general use ciphers with private key.

In 1963, the American mathematician Claude Shannon, with the help of the ciphers developed by him, mathematically proved that in all classical ciphers, the following encryption methods, such as mixing ciphers and scattering ciphers, can be distinguished as typical components.

The essence of the dispersion cipher is the redistribution of the redundancy of the original, which is in different places in the plaintext. To do this, substitutions with a finite number of elements Π are used, which is an unknown key. Thus, the number of all possible keys is equal to P.

When decrypting, use the inverse substitution matrix. Such encryption, although it does not affect the frequency of the appearance of letters, but will hide the frequency of the appearance of bigrams, trigrams, etc. The essence of the cipher of mixing is that the dependence between the key and the encryption of the text make it as difficult as possible. It is better to use substitution with blocks from several characters of the alphabet of the message, although it leads to the fact that the key becomes much longer.

The construction of modern cryptology as a science is based on a combination of concepts and facts of mathematics, physics, information theory , etc. However, despite the complexity, the abundance of theoretical achievements of cryptology is widely used in everyday life, for example, in plastic cards, in e-mail, in Systems of bank payments, with the introduction of databases, electronic voting systems, etc.