  A blockchain is an append-only linked-list of blocks, which is maintained at
each participating node. Each block records a set of transactions and their
associated metadata. Blockchain transactions act on the identical ledger data
stored at each node. Blockchain was first perceived by Satoshi Nakamoto as a
peer-to-peer digital-commodity (also known as crypto-currency) exchange system.
Blockchains received traction due to their inherent property of
immutability-once a block is accepted, it cannot be reverted.
