Notes

BitAddress: "BitAddress - Blockchain for Bitcoin". Retrieved March 19, 2019.
Given a starting point, following the ledger backward, after six confirmation times, one can only have very strong confidence that a bitcoin was not spent as long as it had not been included in a block that has been confirmed. This strongly suggests that each bitcoin exists only once in the entire history of the network. This is a significant advantage of the blockchain.

Blockchain innovation

Bitcoin innovator Satoshi Nakamoto is credited with creating the first blockchain in a 2008 publication.

As mentioned, a blockchain is a publicly accessible, append-only database that is continuously growing and updated. It can be updated via transaction inputs and outputs or mined via miners.

A transaction input is a reference to a prior transaction output. https://pin-up-casino-br.com/ A transaction output can be spent by creating a new transaction that contains a valid spend. This is the primary method by which miners add transaction records to the blockchain in order to extend it and generate transaction fees. Miners are rewarded through transaction fees for the validation of newly discovered blocks.

A blockchain is typically stored redundantly on a peer-to-peer network, but it can also be stored in a single location that requires maintenance by a trusted third party. One advantage of storing multiple copies of the blockchain is that in case one copy of the blockchain is lost, it is still possible to reconstruct the transactions in the blockchain. This functionality is provided by a wide variety of blockchain software and other services. The ability of a client to independently produce a blockchain without the aid of a trusted third party is a property called Byzantine fault tolerance.

An alternative to a blockchain is a distributed ledger, like a shared database or a timestamp server. Distributed ledgers are not the same as a blockchain. In a blockchain, as data is added to the ledger, each ledger entry is permanently linked to all previous and subsequent entries in the chain. Distributed ledgers can be "forged" when changing the contents of a distributed ledger. A distributed ledger typically only stores read-only data. It does not contain a chain of blocks with a linked ledger of transaction details, as a blockchain does. A distributed ledger is not as cryptographically secure as a blockchain.

In 2008, a paper was published by Microsoft's Hyperledger Project on a blockchain database technology called Fabric. Fabric does not use cryptography, instead relying on a distributed consensus technique to control access to shared transaction data and prevent double spending.

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