Paper 2020/1580

Achieving State Machine Replication without Honesty Assumptions

Conor McMenamin and Vanesa Daza and Matteo Pontecorvi

Abstract

State machine replication protocols have reached a crucial juncture in their widespread deployment. Tokenised state machine replication protocols, which utilise an internal token for rewarding player participation, have brought about major advances in the areas of finance, internet of things, supply chain, legal systems, and data storage, to name but a few. However, the viability of these protocols as replacements for their centralised alternatives requires guarantees of player actions at all times which at present do not exist. Current standards for player characterisation in tokenised state machine replication protocols allow for honest players who will always follow the protocol, regardless of possible token increases for deviating. Given the ever-increasing market capitalisation of these tokenised protocols, honesty is becoming more expensive and more unrealistic. As such, this out-dated player characterisation must be removed to provide true guarantees of safety and liveness in a major stride towards universal trust in state machine replication protocols and a new scale of adoption. As all current state machine replication protocols are built on these legacy standards, it is imperative that a new player model is identified and utilised to reflect the true nature of players in tokenised protocols, now and into the future. To this effect, we propose the ByRa player model for state machine replication protocols. In the ByRa model, players either attempt to maximise their tokenised rewards, or behave adversarially. This merges the fields of game theory and distributed systems, an intersection in which tokenised state machine replication protocols exist, but on which little formalisation has been carried out. In the ByRa model, we identify the properties of strong incentive compatibility in expectation and fairness that all protocols must satisfy in order to achieve state machine replication. We then provide FAIRSICAL, a protocol which provably satisfies these properties, and by doing so, achieves state machine replication in the ByRa model.