Blockchain

Blockchain is a chain or list of blocks. Each block in the blockchain has its own digital signature or cryptographic hash, which contains digital signature of the previous block, and it has data including state data and transaction data. Each block is generated within a specific epoch (i.e., period of time) and pointed towards its parent in the blockchain, forming along chain of hashed blocks. Ethereum is a blockchain-based decentralized platform featuring smart contract functionality [7]. Ethereum supports a variant of Nakamoto consensus via transaction-based state transitions. It supports stateful contracts in which values can persist on the blockchain to be used in multiple invocations.

The components of an open, public blockchain are (usually):

• A peer-to-peer (P2P) network connecting participants and propagating transactions and blocks of verified transactions, based on a standardized "gossip" protocol
• Messages, in the form of transactions, representing state transitions
• A set of consensus rules, governing what constitutes a transaction and what makes for a valid state transition
• A state machine that processes transactions according to the consensus rules
• A chain of cryptographically secured blocks that acts as a journal of all the verified and accepted state transitions
• A consensus algorithm that decentralizes control over the blockchain, by forcing participants to cooperate in the enforcement of the consensus rules
• A game-theoretically sound incentivization scheme (e.g., proof-of-work costs plus block rewards) to economically secure the state machine in an open environment
• One or more open source software implementations of the above ("clients")