Blockchain, otherwise a block chain, is a technology that is used to store and transmit information about transactions concluded on the Internet. This information is arranged in the form of successive blocks of data. One block contains information about a certain number of transactions, then after it is saturated, another block of data is created, and then another and another, creating a kind of chain. Information about various types of transactions can be sent in it, e.g. commercial, purchase or sale of currencies, including cryptocurrencies.

The main essence of blockchain operation is to maintain a common and collective ledger of transactions in digital form, distributed over the network, in the same copies. This technology is based on a peer-to-peer network without central computers, management systems and transaction verification. Any computer connected to the network can participate in the transmission and authentication of transactions. This book, thanks to complex cryptographic tools, is fully protected against unauthorized access, and at the same time it is open to everyone. The user can view and verify the entire transaction history from the very beginning of the blockchain to the present day.

At the moment, blockchain can be used to handle various transactions, e.g. trade, electricity market, currencies. However, work is underway on the use of blockchains for digital signatures in state administration or as an accounting ledger in banking. These transactions can take place outside the system that has been functioning for centuries – without the participation of public trust institutions, directly between the parties to the transaction. Any type of transaction can be stored in blockchain technology. One of the applications can be cryptocurrencies, e.g. bitcoin. Blockchain technology has found recognition in many industries, including financial or energy.

With the current technology and computing power of computers, it is impossible to counterfeit the largest blockchains. It is estimated that to crack a blockchain network, you would need computing power equal to half the Internet. However, the introduction of quantum computers will require the implementation of new cryptographic security, which should not be a big problem.