On the Round Complexity of Asynchronous Crusader Agreement

Authors Ittai Abraham, Naama Ben-David, Gilad Stern, Sravya Yandamuri

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Author Details

Ittai Abraham
  • Intel Labs, Petah Tikva, Israel
Naama Ben-David
  • Technion, Haifa, Israel
Gilad Stern
  • The Hebrew University of Jerusalem, Israel
Sravya Yandamuri
  • Duke University, Durham, NC, USA

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Ittai Abraham, Naama Ben-David, Gilad Stern, and Sravya Yandamuri. On the Round Complexity of Asynchronous Crusader Agreement. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 29:1-29:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)


We present new lower and upper bounds on the number of communication rounds required for asynchronous Crusader Agreement (CA) and Binding Crusader Agreement (BCA), two primitives that are used for solving binary consensus. We show results for the information theoretic and authenticated settings. In doing so, we present a generic model for proving round complexity lower bounds in the asynchronous setting. In some settings, our attempts to prove lower bounds on round complexity fail. Instead, we show new, tight, rather surprising round complexity upper bounds for Byzantine fault tolerant BCA with and without a PKI setup.

Subject Classification

ACM Subject Classification
  • Theory of computation → Distributed algorithms
  • lower bounds
  • asynchronous protocols
  • round complexity


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