Blockchain is a technology used to store data and create decentralized computer networks. It is based on the concept of an immutable chain of blocks, in which information about the performed operations (transactions) is recorded. In essence, this is a kind of ledger that is distributed among the participants in this network in such a way that each of them has an exact copy of the blockchain, updated synchronously. The active use of Blockchain began in 2009 when it was used by Satoshi Nakamoto when creating bitcoin. In this case, the Bitcoin blockchain includes blocks of user transactions. Each subsequent block is synchronized with all previous ones. Once written to the blockchain, it cannot be changed. This is a chain of blocks containing a strict sequence of data. They contain information in the form of a cryptographic cipher about the transactions performed, namely:

• transactions;
• contracts;
• transactions in the systеm.

The blocks are arranged in a sequence and are inextricably linked with each other. To get a new element, you need to know the data about previously created links. Important! Blockchain is constantly updated and its database is limitless. It can record information about a myriad of transactions. The systеm cannot dеlete any element or rеplace a block. This is the main advantage of blockchain. The elements of the chain contain a certain set of data and a new block cannot be created until the previous one is closed, since each contains a key with a long sequence of random letters and numbers. There may be more than a million characters. Until it is solved using cryptography, the block will not close. The process is monitored by miners, whose main task is to perform a series of computational operations to find a cryptographic signature. As soon as it is found, the block is closed and the miners are rewarded. Blockchain is supported by computers all over the world. No server can be hacked. The security of the systеm is provided by miners and owners of cold wallets, who store the downloaded version of the Blockchain on the PC. They are called nodes or nodes. The more of them, the faster the data on the financial transactions of the old block will be processed and a new element will be opened. This usually takes 10 minutes. Blockchain technology can be used not only in the field of cryptocurrencies. It can be used during elections, personal identification, document management, logistics, copyright protection, etc. Today, significant hopes are placed on the blockchain for having the potential to eradicate corruption, intermediaries, and bureaucracy in case of global use and are compared in their importance with the advent of the Internet.