So we have our cryptographic hash functions that link blocks of data in a chain. We have our proof-of-work mechanism that incentivises new blocks to be added to a chain and helps ensure against bad actors by requiring a computational proof for each block.
The final way that blockchain’s ensure security is by being distributed.
Blockchain’s run on what’s called a peer-to-peer (P2P) network – mentioned in the Satoshi quote above.
What is a Peer-to-Peer Network?A network of users that communicate directly with each other and share the same privileges.
Rather than being centralised and run by a single entity – such as government – P2P networks are made up of a distributed network of computers all following the same set of rules (protocol)., In this way, everyone of those computers connected to the blockchain has access to the full record (or chain) but behaves in a predictable way.
Each time a new block is added to the chain, everyone has the chance to verify this block’s data as accurate. Any computer that connects and runs a blockchain is called a node.
For a block to be added to the chain at least 51% (a majority) of all nodes, have to agree that it is accurate. In other words, that the proof of work has been solved and the hash functions all match. This is called achieving consensus – creating a shared agreement of truth in our magical solution to our trust. All without any central authority.
To successfully corrupt a blockchain you need to
- Tamper with all the blocks on the chain.
- Redo the proof of work for every block.
- Take control of more than 50% of the P2P network
Not only is this almost impossible to do, with the difficulty growing as the number of nodes grows, it doesn’t make economic sense. Thus, blockchain’s are a secure and decentralised way of storing data, with those qualities improving as the blockchains grow..
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