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Weaker Assumptions for Asymmetric Trust

Authors Ignacio Amores-Sesar , Christian Cachin , Simon Holmgaard Kamp , Juan Villacis

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Subject Classification

ACM Subject Classification
  • Theory of computation → Distributed algorithms
Keywords
  • Asymmetric Trust
  • Quorum Systems
  • Reliable Broadcast
  • Consensus

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Abstract

In distributed systems with asymmetric trust, each participant is free to make its own trust assumptions about others, captured by an asymmetric quorum system. This contrasts with ordinary, symmetric quorum systems and threshold models, where trust assumptions are uniformly shared among participants. Fundamental problems like reliable broadcast and consensus are unsolvable in the asymmetric model if quorum systems satisfy only the classical properties of consistency and availability. Existing approaches overcome this by introducing stronger assumptions. We show that some of these assumptions are overly restrictive, so much so that they effectively eliminate the benefits of asymmetric trust. To address this, we propose a new approach to characterize asymmetric problems and, building upon it, present algorithms for reliable broadcast and consensus that require weaker assumptions than previous solutions. Our methods are general and can be extended to other core problems in systems with asymmetric trust.

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Ignacio Amores-Sesar, Christian Cachin, Simon Holmgaard Kamp, and Juan Villacis. Weaker Assumptions for Asymmetric Trust. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 8:1-8:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025) https://doi.org/10.4230/LIPIcs.OPODIS.2025.8

Author Details

Ignacio Amores-Sesar
  • Aarhus University, Denmark
Christian Cachin
  • University of Bern, Switzerland
Simon Holmgaard Kamp
  • Ruhr University Bochum, Germany
Juan Villacis
  • University of Bern, Switzerland

Funding

This work was supported by the Swiss National Science Foundation (SNSF) under grant agreement Nr . 219403 (Emerging Consensus), by the Initiative for Cryptocurrencies and Contracts (IC3), by the Cryptographic Foundations for Digital Society, CryptoDigi, DFF Research Project 2, Grant ID 10.46540/3103-00077B, and by the European Union, ERC2023-StG-101116713. Views and opinions expressed are those of the author(s) only and do not necessarily reflect those of the European Union. Neither the European Union nor the granting authority can be held responsible for them.

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