As per Imran Bashir in his book Mastering Blockchain, a blockchain can be defined as “a peer-to-peer, distributed ledger that is cryptographically secure, append-only, immutable (extremely hard to change), and updateable only via consensus or agreement among peers.” In simple terms, a blockchain is an ever-growing secure record-keeping database of transactions that have taken place between two network participants (parties). This database—known as a distributed ledger—logs blocks of data containing information, known as metadata, about each transaction being added to the blockchain in chronological order upon verification of each block.