Recent Latest Message Driven GHOST: Balancing Dynamic Availability With Asynchrony Resilience

Dynamic participation has recently become a crucial requirement for devising permissionless consensus protocols. It enhances robustness against events involving portions of participants going offline, thus preserving the safety and liveness of such dynamically available protocols. This concept, formalized by Pass and Shi (ASIACRYPT 2017) through the sleepy model, has been implicitly adopted to model various blockchain protocols, such as Ethereum's consensus protocol, Gasper. Neu, Tas, and Tse (S&P 2021) demonstrated that LMD-GHOST, Gasper's dynamic availability component, is not secure even in a full-participation context, i.e., with all validators online. Subsequent mitigations were developed to address its shortcomings. However, the resulting protocol still fails to achieve dynamic availability, motivating further research into more secure, dynamically available protocols. In this work, we introduce RLMD-GHOST, a synchronous, dynamically available protocol that maintains safety during bounded periods of asynchrony. This protocol is particularly appealing for practical systems where strict synchrony assumptions may not always hold, contrary to general assumptions in standard synchronous protocols. Additionally, we present the generalized sleepy model, within which our results are proven. Building upon the original sleepy model proposed by Pass and Shi, this model extends it with more generalized and stronger constraints on the corruption and sleepiness power of the adversary. This approach allows us to explore a wide range of dynamic participation regimes, spanning from complete dynamic participation to no dynamic participation, i.e., with every participant online. Consequently, this model provides a foundation for analyzing dynamically available protocols.