The blockchain is a set of linked blocks, containing transactions and which can under no circumstances be altered (principle of immutability) because protected via processes that have been proven.
here is a simplified representation of the blockchain registry which is a set of blocks (containing all the transactions) and linked together by the concatenation of their respective hash that is passed to each new block
Each block is identified by a hash (fingerprint) which is an alpha-numeric character string to identify the block. And each of these blocks contains the hash of the preceding block to which it adds its own hash. The 1st block of a blockchain called the block Genesis (original block) contains only its own hash because being the first block of the long chain of blocks that will follow.
the blockchain is therefore a gigantic register consisting of blocks containing transactions and which has the following characteristics:
- Fully decentralised (no central control organ)
- Freely accessible (possibility to consult all transactions in a public way)
- Secured by special nodes of the network called "miners" and which makes any piracy almost impossible
The ultimate goal of the blockchain is to terminate the intermediaries system (which can pose many concerns because their operation is inherently opaque) through the decentralization of transactions.
the main concerns in a system of exchanges with the presence of an intermediary being:
- The risk of tampering with transactions
- A flagrant lack of transparency of operations performed (opacity)
- Additional time and money costs for those who carry out transactions
The blockchain allows:
- Faster transaction execution
- Transparency of transactions (one can publicly check the status of a transaction)
- A significantly reduced cost (in terms of time and money in particular) for those who carry out transactions (because there is no intermediary between them).
Each of the blocks that compose a blockchain are validated and created by an ingenious verification system that solicits specialized network nodes called "miners" .
Illustrated example of validating a new block by special network nodes called "miners"
The latter are intended to create new blocks as soon as they manage to solve some sort of very complex mathematical problem proposed via a consensus system.
each time that a minor finds the solution to the mathematical problem proposed by the consensus system, the block is considered valid and is added to the other blocks of the blockchain.
finally in a blockchain system each participant of the network holds a copy of the registry of the latter. This is why the blockchain is considered a distributed and decentralized database .
therefore if a malicious person wishes to alter a blockchain it could not because to do so it would be necessary that the majority of nodes of the network accept this alteration which would not be in their interest.
This allows the blockchain to continue to function because all participants have more interest in cooperating together rather than attempting to corrupt the system by acting on an individual basis.
Illustrated example of a fork
However in some very specific cases a blockchain can split into two it is called a «fork».