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Lifeline: Optimal Validated Byzantine Agreement Under Minimal Synchrony

Authors Yuval Efron , Ling Ren

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LIPIcs.DISC.2026.11.pdf
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Subject Classification

ACM Subject Classification
  • Theory of computation → Distributed algorithms
Keywords
  • Byzantine agreement
  • granular synchrony
  • optimal communication complexity

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Abstract

The synchronous model allows solutions to (variants of) Byzantine Agreement (BA) to be deterministic and achieve the asymptotically optimal O(n) rounds and O(n²) bits of communication where n is the number of parties. In this paper, we study deterministic protocols for the validated BA problem in a model in which every communication link is either synchronous or partially synchronous. Our main result is that in the region of an honest majority, feasibility implies optimality: For every f < n/2, the minimal network conditions required for validated BA to be solvable against f byzantine faults, are also sufficient for it to be solvable optimally, i.e., with O(f) rounds and O(f²) communication. In particular, validated BA against minority byzantine faults can be solved when the synchronous links in the network form a mere path (f synchronous links) as efficiently (up to constant factors) as when all communication links are synchronous (Ω(f²) synchronous links).

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Yuval Efron and Ling Ren. Lifeline: Optimal Validated Byzantine Agreement Under Minimal Synchrony. In 40th International Symposium on Distributed Computing (DISC 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 397, pp. 11:1-11:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026) https://doi.org/10.4230/LIPIcs.DISC.2026.11

Author Details

Yuval Efron
  • Institute for Advanced Study, Princeton, NJ, USA
Ling Ren
  • University of Illinois Urbana-Champaign, Urbana, IL, USA

Funding

This work is funded in part by the National Science Foundation award #2143058.

References

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