Blockchain offers the same record-keeping functionality but without a centralised architecture. The question is how it can be certain that a transaction is legitimate when there is no central authority to check it. Blockchains solve this problem by decentralising the ledger, so that each user holds a copy of it. Anyone can request that any transaction be added to the blockchain, but transactions are only accepted if all the users agree that it is legitimate, e.g. that the request comes from the authorised person, that the house seller has not already sold the house, and the buyer has not already spent the money. This checking is done reliably and automatically on behalf of each user, creating a very fast and secure ledger system that is remarkably tamper-proof.Each new transaction to be recorded is bundled together with other new transactions into a 'block', which is added as the latest link on a long 'chain' of historic transactions. This chain forms the blockchain ledger that is held by all users. This work is called 'mining'. Anybody can become a miner and compete to be the first to solve the complex mathematical problem of creating a valid encrypted block of transactions to add to the blockchain. There are various means of incentivising people to do this work. Most often, the first miner to create a valid block and add it to the chain is rewarded with the sum of fees for its transactions. Fees are currently around €0.10 per transaction, but blocks are added regularly and contain thousands of transactions. Miners may also receive new currency that is created and put into circulation as an inflation mechanism.
Adding a new block to the chain means updating the ledger that is held by all users. Users only accept a new block when it has been verified that all of its transactions are valid. If a discrepancy is found, the block is rejected. Otherwise, the block is added and will remain there as a permanent public record. No user can remove it. While destroying or corrupting a traditional ledger requires an attack on the middleman, doing so with a blockchain requires an attack on every copy of the ledger simultaneously. There can be no 'fake ledger' because all users have their own genuine version to check against. Trust and control in blockchain-based transactions is not centralised and black-boxed, but decentralised and transparent. These blockchains are described as 'permissionless', because there is no special authority that can deny permission to participate in the checking and adding of transactions. They can also be described as embodying social and political values such as transparency and the redistribution of power.