International Association for Cryptologic Research

International Association
for Cryptologic Research


State Machine Replication under Changing Network Conditions

Andreea Alexandru , University of Maryland, College Park
Erica Blum , University of Maryland, College Park
Jonathan Katz , University of Maryland, College Park
Julian Loss , CISPA Helmholtz Center for Information Security
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Presentation: Slides
Conference: ASIACRYPT 2022
Abstract: Protocols for state machine replication (SMR) are typically designed for synchronous or asynchronous networks, with a lower corruption threshold in the latter case. Recent network-agnostic protocols are secure when run in either a synchronous or an asynchronous network. We propose two new constructions of network-agnostic SMR protocols that improve on existing protocols in terms of either the adversarial model or communication complexity: 1. an adaptively secure protocol with optimal corruption thresholds and quadratic amortized communication complexity per transaction; 2. a statically secure protocol with near-optimal corruption thresholds and linear amortized communication complexity per transaction. We further explore SMR protocols run in a network that may change between synchronous and asynchronous arbitrarily often; parties can be uncorrupted (as in the proactive model), and the protocol should remain secure as long as the appropriate corruption thresholds are maintained. We show that purely asynchronous proactive secret sharing is impossible without some form of synchronization between the parties, ruling out a natural approach to proactively secure network-agnostic SMR protocols. Motivated by this negative result, we consider a model where the adversary is limited in the total number of parties it can corrupt over the duration of the protocol and show, in this setting, that our SMR protocols remain secure even under arbitrarily changing network conditions.
Video from ASIACRYPT 2022
  title={State Machine Replication under Changing Network Conditions},
  author={Andreea Alexandru and Erica Blum and Jonathan Katz and Julian Loss},