Blockchain allows every participant in a network to access a distributed database. Blockchain does not store data but records events (transactions) in chronological order.

All new records are checked for authenticity - they must be confirmed by the majority of the network members before they can be entered into the blockchain. Records are grouped into blocks, which are combined into chains. Once data is on the blockchain, it cannot be altered or deleted without breaking the blockchain's integrity.

Types of blockchain

Blockchain can operate both on a public (open) network, to which any user has access, and on a private (closed) network, such as a corporate network in the case of sensitive data. Private versions of blockchain can have different levels of access for users and different levels of complexity for encrypting information.

The best-known example of a public blockchain is bitcoin, chainlink news, and other cryptocurrencies. Corporations use blockchain not only in the financial sector but also in other sectors, such as the entertainment industry (for issuing tickets) and healthcare (to protect patient data).

There are also hybrid networks that combine features of both open and closed networks.

By transaction object:
- information;

- virtual value (a value whose counterpart does not exist in the "real world" - for example, bitcoin);

by the type of access to the network:
- Unrestricted (networks in which participants are allowed to perform any activity);

- Limited (networks, which restrict the type of activity of the participants);

by identification requirements:
- anonymous;

- pseudo-anonymous;

- full identification;
- PoW (Proof-of-work) - the right to certify a block is given to a participant based on his performance of some sufficiently complex work, which meets predetermined criteria.

- PoS (Proof-of-stake) - the right to certify a block is given to an account holder when the number of his funds and term of holding them meet the specified criteria. The formulas for calculating the criteria may vary slightly.

- PoS + PoW - a hybrid of PoW and PoS, where blocks can be certified both via calculated PoS criteria and PoW overshoot. The purpose of this approach is to make it harder to recalculate the entire chain (from the very first block), possible when using PoS in its pure form.

- PBFT (Practical Byzantine Fault Tolerance), Paxos, and RAFT are algorithms of multistage network consensus establishment. Algorithms of this group allow blockchain to function with small expenses and have significant bandwidth, but are weakly stable to increase the number of participants.

- Non-BFT (Non-Byzantine Fault Tolerance) - consensus algorithms, unstable to the behavior in which some participants start to work against the network. Such algorithms apply to closed networks with full identification.

In the presence of a central administrator:
- There is a central administrator;

- there is no central administrator