What’s the Blockchain?
The blockchain is a revolutionary technology for record keeping and transactions. It is a distributed ledger technology, which enables decentralized networks. As it is said: “Blockchain is for transactions what the internet was for communication”
In a nutshell
The blockchain is a shared ledger, where every transaction is gathered and recorded in a block, which is subsequently locked. Each block is connected to the previous one and secured by cryptography.
Detailed
The blockchain is like a common register of transactions, used by and visible to all of the members of the network. All blocks contain certain transaction(s), and each new block is connected to all the previous blocks.
The transactions registered on the blockchain are immutable and resistant to change, as changing one transaction would require changing the whole chain.
It is a peer-to-peer network, without one central entity taking control and registering all the activities.
The peers (alias computer nodes) on the blockchain agree via a consensus mechanism on which transaction is valid, and will be registered on the chain.
Smart Contract
It uses the hash function, turning data of any size into a fixed size, and registers transactions in a hash format.
Blockchain technology uses public-key cryptography, where the public key allows others to view transactions made by you, and the secret private key gives you access to your assets on the blockchain.
To grab the essence of blockchain in 20 minutes, check out this amazing Ted talk from Don Tapscott:
https://www.ted.com/talks/don_tapscott_how_the_blockchain_is_changing_money_and_business