How a blockchain works

Blockchain technology has long been touted as a major shake-up in computing. Bitcoin is a perfect example: this cryptocurrency whose value exploded is based on the blockchain principle. The purpose of this article is to describe the operation and main concepts inherent to the implementation of a blockchain. More specific topics such as cryptocurrency analysis or the development of decentralized applications can be the subject of dedicated articles.

What is a blockchain?
A blockchain is by definition a string of blocks. It is comparable to a large virtual registry, in the form of a peer-to-peer network, grouping together a set of transactions made between the users of this network. Each movement registered in the blockchain is for life and is unfalsifiable.

Here is the general principle of a blockchain:

A blockchain has several major interests:

It is transparent: although the exchanges remain anonymous, anyone can consult them.

It is secure: transactions are tamper-proof and secured by protocols based on asymmetric cryptography.

It is independent of any trusted third party: the entire network is responsible for authenticating transactions through the cryptography used.

There are many areas of application such as signing a marriage contract, voting electronically or sending money to the other side of the world. By getting rid of any external trusted third party, a blockchain provides significantly reduced costs and time for the user.

Historical
The first blockchain appeared in 2009 with Bitcoin and uses technology to secure the exchange of its "tokens" (units of account), the bitcoins.

In November 2015, Blockchain technology made the front page of "The Economist". This article greatly accelerates the democratization of the subject, which was until now still reserved for the initiated.