부산대학교 도서관

Summary: ``Protocols for state machine replication (SMR) are typicallydesigned for synchronous or asynchronous networks, with a lowercorruption threshold in the latter case. Recent {\it network-agnostic}protocols are secure when run in either a synchronous or anasynchronous network. We propose two new constructions ofnetwork-agnostic SMR protocols that improve on existing protocols interms of either the adversarial model or communication complexity:\roster\item"1." an {\it adaptively} secure protocol with optimal corruption thresholdsand quadratic amortized communication complexity per transaction;\item"2." a statically secure protocol with near-optimal corruption thresholdsand {\it linear} amortized communication complexity per transaction.\endroster We further explore SMR protocols run in a network that may changebetween synchronous and asynchronous arbitrarily often; parties can beuncorrupted (as in the proactive model), and the protocol should remainsecure as long as the appropriate corruption thresholds are maintained.We show that purely asynchronous proactive secret sharing is impossiblewithout some form of synchronization between the parties, ruling out anatural approach to proactively secure network-agnostic SMR protocols.Motivated by this negative result, we consider a model where theadversary is limited in the total number of parties it can corrupt overthe duration of the protocol and show, in this setting, that our SMRprotocols remain secure even under arbitrarily changing networkconditions.''MR