QPoS: Decentralized Stake-Based Leader and Voter Selection in a PBFT System With Mobile Voters

Abstract

Both Proof of Stake (PoS) and Delegated Proof of Stake (DPoS) consensus schemes for permissioned blockchains incur the risk of centralization of voting power in the hands of a small number of wealthy voters. In this work, we present Qualified Proof of Stake (QPoS) scheme which alleviates centralization by rewarding truthful behavior of both voters and leaders, and penalizing their untruthful behavior. Leaders are elected according to the current stake which gives preference to more trustworthy nodes. Nodes with low stake at the end of a round which consists of multiple PBFT voting cycles are excluded from voting in subsequent rounds, while nodes with sufficient stake may leave the network temporarily without losing their stake. We consider multiple node classes with different voting behavior and model them using embedded Markov Chain which corresponds to Semi Markov Process (SMP) in order to determine system performance. Our results show the interaction of class populations, voting behavior, and mobility with round size, and show notable stake-based prioritization among the nodes for selection of PBFT leaders. Moreover, we show that higher proportion of well behaved nodes and shorter voting rounds are needed to achieve consensus with high probability.