Blockchain is increasingly becoming more important with the popularity of variant cryptocurrencies such as bitcoin, ethereum, and litecoin. A blockchain is a growing list of records, called blocks, each block contains a cryptographic hash of the previous block, a timestamp and transaction data. Blockchain is open and distributed ledger that records transactions between two parties in a permanent and verifiable way. It does not support the modification of data, and is based on P2P network, adhering to a protocol for inter-node communication and validating new blocks. Even though blockchain records are not unalterable, it is considered secure by design and a good example of a distributed computing system.
Blockchain is invented by a person or group of people using the name of Satoshi Nakamoto in 2008 with the creation of bitcoin. Satoshi Nakamoto is an unknown geek or hacker, but his invention of blockchain did solve the double-spending problem with the demand of a trusted authority or central server. Blockchain is therefore claimed with a decentralization, readable by the public and got widely used by cryptocurrencies. It is considered a type of payment rail, a private blockchain is proposed for business use.
Currently, there are basically four types of blockchain networks — public blockchains, private blockchains, consortium blockchains, and hybrid blockchains. It is accessible by anyone from the Internet without restrictions. Bitcoin is the best known public blockchains. Private blockchains, on the other hand, denies the joint unless administrators send out an invitation to the participants. This is usually accepted by middle ground companies that are interested in blockchain but not comfortable with a level of control offered by public networks. A consortium blockchain is permissioned by a single organization, so it is said to be semi-decentralized. A hybrid blockchain is in between, regarding different characteristics of both public and private blockchains. It allows determining what information stays private and what information is made public.
Blockchain technology can be integrated into multiple areas, the primary use of it is as a distributed ledger for cryptocurrencies, a few operational products maturing from proof of concept by late 2016. Besides cryptocurrencies, blockchain is combined with smart contracts, financial services, supply chain, etc.