3.2 Smart Contract Over Different Blockchain Implementations Blockchain has evolved from merely having a use case of being a peer-to-peer network to process cryptocurrency transactions, where participating nodes enact consensus protocols, to function as state machines that consistently track transitions to data and states jointly manipulated by a number of clients. This tamperproong sequence of blocks and the anonymity around it has attracted entities and users willing to share consent between mutually-untrusted parties. This blockchain feature has enabled a generallypurposed and distributed computing platform. Blockchain technology helps implement smart contracts in multiple ways, such as implementing stricter admission rules for new agents, thus allowing for ner access control and the concept of peer-permissioning. Some of the prime blockchain implementations and their interactions with smart contracts are described below.

Ethereum: is a permissionless blockchain implementation that allows both node accounts and smart contract accounts to hold balance in Ether the native cryptocurrency of Ethereum implementations. The smart contract encapsulates custom and stateful behaviors, for which miner nodes could run the hexadecimal bytecode data of the transaction with its Ethereum Virtual Machine (EVM), which is the execution environment for running transaction code to reach a consensus. Smart contracts are compiled with EVM to generate operation codes (e.g. PUSH1 0x60 PUSH1 0x40 MSTORE) and run based on the operation codes each time a specic method in the smart contract related to a specic transaction is invoked following the rules set within the deployed smart contract. The smart contract could then have states transitioned on each miners local persistent storage on state data, only if data of the transaction is executed by the EVM successfully. There are also a variety of transaction types in Ether

Ethereum does not encourage complex computation steps and long computation time in smart contracts through the concept of fuel included in the transaction called "Gas". There is also

4 a permissioned implementation of Ethereum with a consensus algorithm of PoA (Proof-of-Authority) with peer-permissioning and on-chain governance enabled, which are covered in , . Hyperledger Fabric: is a permissioned blockchain implementation in which nodes consisting of "Ordering Service" are in charge of a consensus protocol. The roles of the miners are assigned by the "Membership Service", along with their membership verication and nodes that have access to the ledger are called "peers", and each peer belongs to some organizations. Smart contracts could be dynamically installed and executed in any given channel.