Fork-Free Hybrid Consensus with Flexible Proof-of-Activity

Bitcoin and its underlying blockchain mechanism have been attracting much attention. One of their core innovations, Proof-of-Work (PoW), is notoriously inefficient which potentially motivates a centralization of computing power, defeating the original goal of decentralization. Proof-of-Stake (PoS) is later proposed to replace PoW. However, both PoW and PoS have different inherent advantages and disadvantages, so does Proof-of-Activity (PoA) of Bentov et al. (SIGMETRICS 2014) which only offers limited combinations of two mechanisms. On the other hand, the hybrid consensus protocol of Pass and Shi (ePrint 16/917) aims to improve the efficiency by dynamically maintaining a rotating committee. Yet, there are unsatisfactory issues including chain forks and fair committee election. In this paper, we firstly devise a generalized variant of PoW. After that, we leverage our newly proposed generalized PoW to construct a fork-free hybrid consensus protocol, which addresses issues faced by the existing hybrid consensus mechanism. We further combine our fork-free hybrid consensus mechanism with PoS for a flexible version of PoA, which offers a flexible combination of PoW and PoS. Compared with Bentov et al.’s PoA, our “flexible PoA” improves the efficiency and provides more flexible combinations of PoW and PoS, resulting in a more powerful and applicable consensus protocol.