A blockchain – originally block chain – is a distributed database that maintains a continuously growing list of ordered records called blocks. Each block contains a timestamp and a link to a previous block. By design, blockchains are inherently resistant to modification of the data — once recorded, the data in a block cannot be altered retroactively. Blockchains are secure by design and an example of a distributed computing system with high byzantine fault tolerance. Decentralised consensus can therefore be achieved with a blockchain. This makes blockchains suitable for the recording of events, medical records, and other records management activities, identity management, transaction processing, and proving data provenance.