A blockchain is a distributed database that is shared by a network of computers (distributed ledger). When a record is added to a block (ledger), it becomes immutable. To ensure that all copies of the database are identical, network nodes constantly check to ensure they have the most recent version of the blockchain. The focus of blockchain is on decentralised peer-to-peer transactions (currencies or digital assets), which are not controlled by a single centralised entity. The database is completely transparent and keeps a history of all transaction data. Blockchains, on the other hand, are protected by complex cryptographic rules and can only be accessed using public and private keys.