How does blockchain work?

The blockchain is an autonomous and encrypted storage technology, invented in 2008 by the creator of bitcoin. In fact, it is a kind of database without control of a higher authority and whose security is guaranteed by digital cryptography techniques. The database is powered by users who enter the information they want to store.

Each block of data is dated and connected to the one produced before it in the same chain. Before moving on to the next one, the contents of each block must be checked by users and validated. Once added, a block of data can not be modified or deleted. The set thus creates a chain of dated and unalterable data.

Simply put, transactions between network users are grouped into blocks. Each block is validated by the nodes of the network called the “minors”, according to techniques that depend on the type of blockchain. In the bitcoin blockchain this technique is called “Proof-of-Work”, proof of work, and consists in solving algorithmic problems.

Once the block is validated, it is time stamped and added to the blockchain. The transaction is then visible to the receiver as well as the entire network. Here are the steps then:

Steps of a blockchain


  • Once a transaction is performed, it is grouped with others within a block then it can not be changed.
  • The miners validate the block by cryptographic techniques helps.
  • After the validation of the block, it is added to the blockchain accessible to all users. Remember that nothing can be modified or deleted: it would be necessary to add a new transaction in case of error.
  • The transaction is time stamped and finalized.


Actually; checksum, which is like a footprint is a number, it is calculated from the contents of the block, as it is impossible to reconstruct the block from its checksum so that is why the block completely edits the checksum. In the case of Bitcoin, it is a 256-bit number, whose number of distinct values ​​is expressed by a number of 78 digits. Two blocks with different contents always have different checksums. The checksum of a block can therefore serve as a unique identifier.


However, let’s see what a block is. It is the grouping of a certain number of elementary writings, whose form and meaning depend on the application. In the case of Bitcoin or other payment systems, they are monetary transactions, and each block typically contains between 1000 and 3000. Completed by a header which, the block contains among other things the identifier of the previous block, so its own checksum. From any block, one can thus go up to the initial block of the chain while checking at each step its validity.


At every access, the hash of a block is systematically verified in order to detect any modification made to its content after its construction. If the author of the change also modified the block header by including his new checksum, he modified his identifier at the same time. To introduce in the chain a modified block would thus force to modify the headers of all the following blocks, an operation all the more expensive as the block is older, and that the calculation of the checksums is itself made more consumer resources by imposing very severe constraints.