Blockchain. Aislamiento web

Also known as chain of blocks or distributed ledger, blockchain is a decentralized technology.

It origins date back to 1991, but it didn´t become popular until 2009, when Satoshi Nakamoto used it to create bitcoin, the most famous cryptocurrency.

• There are no intermediaries: the data is shared by all the nodes. The nodes, independent from each other, register and validate the information.
• There are no nodes that control others, nor do any of them have different information,
• The chain of blocks is a type of distributed ledger, completely open (depending on whether it is a permissioned one or not) and anyone can join it and participate.
• In most cases, once recorded, the data cannot be altered. It will only be possible to add new records. The data will not be legitimized until almost all nodes agree to do so (consensus). As a result, a change in one of the copies would have no effect, it would be necessary to change them all.
• A blockchain is typically managed by a peer-to-peer network where all the nodes are equal. This structure offers great resistance against cyberattacks, failures or falsifications (for a chain of blocks to be hacked, almost all nodes must get hacked. Otherwise, since each block depends from the previous one, the attack will have no effect).

In case of a network failure, only one node would need to work in order to keep the data safe.

All the nodes share the same structure (except for the first one, also known as genesis block):

• Nonce: is an arbitrary number that can only be used once.
• Merkle Tree: structure that summarizes all the transactions in a block within a specific period of time. By doing so, a Merkle Tree helps verify the consistency and content of the data.
• Cryptographic hash: it is an alphanumeric code of the previous block. It makes it possible to organize the blocks in chronological order. Only those blocks that have a valid hash can join the chain.

Merkle trees are a fundamental part of the blockchain technology. This structure helps verify the consistency and content of data. Merkle trees are used by both Bitcoin and Ethereum.

Each time a block is confirmed and added to the chain, it is communicated to the rest and added to the copy of each one.

If something changes within the block, the hash changes (hence its usefulness to detect the changes that have been made). If the digital proof changes, the block will no longer be the same.

As if this were not enough, blockchain also adds a last security element: the Proof of Work (PoW). This mechanism slows down the large capacity of computers to calculate large amounts of hashes per second and thus decelerate the creation of new blocks.

Besides the famous cryptocurrency bitcoin, blockchain can be used in countless scenarios. To name a few:

• Electronic vote
• Creation of smart contracts
• Tax collection
• Reduction of degree fraud
• Improved security in online purchases

• Protection of medical records
• Reduction of the time and fees associated with internal transfers
• Creation of digital notaries
• Product information (i.e: origin)
• Control and monitoring of artistic work by its authors

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