A probabilistic Proof-of-Stake protocol with fast confirmation

Abstract

Proof-of-Stake (PoS) protocol is one of the most promising blockchain consensus protocols in the permissionless setting. However, there is a general problem of slow confirmation in PoS protocol. To address the issue, a small-sized committee in PoS protocol is used to reduce the costs in terms of communication and computation, and accelerate confirmation. Following this idea, a committee-based PoS protocol called LaKSA (NDSS’2021) is proposed recently.In this paper, we present a balance attack on LaKSA, and show LaKSA cannot satisfy the liveness property even in the synchronous network. To ensure security and improve efficiency, we propose a self-healing probabilistic PoS protocol with a small-sized committee and a fast confirmation. Specifically, we propose a three-phase broadcast finality gadget and two compatible confirmation rules. The participants can invoke the three-phase broadcast periodically and commit a block according to different confirmation rules. By our approaches, on the one hand, we can prevent the PoS protocol from the balance attack and keep it committing new blocks over time. On the other hand, it empowers the protocol an ability of self-healing, by which nodes can commit a block as quickly as possible instead of waiting for a long time. Furthermore, we prove that our protocol can achieve the security properties of probabilistic safety and liveness. Finally, we conduct extensive experiments to evaluate the performance of the self-healing protocol. The experimental results show that, compared with LaKSA protocol, our protocol improves the commit rate by about 30% with a high throughput under a poor network condition.