  Motivated by proof-of-stake (PoS) blockchains such as Ethereum, two key
desiderata have recently been studied for Byzantine-fault tolerant (BFT)
state-machine replication (SMR) consensus protocols: Finality means that the
protocol retains consistency, as long as less than a certain fraction of
validators are malicious, even in partially-synchronous environments that allow
for temporary violations of assumed network delay bounds. Accountable safety
means that in any case of inconsistency, a certain fraction of validators can
be identified to have provably violated the protocol. Earlier works have
developed impossibility results and protocol constructions for these properties
separately. We show that accountable safety implies finality, thereby unifying
earlier results.
