Bitcoin’s Consistency Property

Bitcoin is the most popular cryptocurrency nowadays. Inspired by the success, both industry and academia seek to apply Bitcoin's core technique, Blockchain, to other fields like finance, healthcare and Internet-of-Things. One main application is to use Blockchain as the distributed transaction ledger system, a ledger (or a log) of all transactions that is maintained by anonymous participants in a distributed fashion. For the ledger system, consistency is an important property which specifies how the system orders the transactions. Intuitively, Blockchain is designed to maintain a single ground truth - the chain itself is the order of the transactions that all participants should respect. However, we show that under some circumstances, Bitcoin violates eventual consistency, i.e., participants would not converge to a single chain. Thus, we urge a more thorough study on Bitcoin's consistency properties. At the end of the paper, we propose related research directions.