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conference paper

Efficient Signature-Free Validated Agreement

Civit, Pierre  
•
Dzulfikar, Muhammad Ayaz
•
Gilbert, Seth
Show more
Alistarh, Dan
October 24, 2024
Leibniz International Proceedings in Informatics, LIPIcs
38 International Symposium on Distributed Computing

Byzantine agreement enables n processes to agree on a common L-bit value, despite up to t > 0 arbitrary failures. A long line of work has been dedicated to improving the bit complexity of Byzantine agreement in synchrony. This has culminated in COOL, an error-free (deterministically secure against a computationally unbounded adversary) solution that achieves O(nL + n2 log n) worst-case bit complexity (which is optimal for L ≥ n log n according to the Dolev-Reischuk lower bound). COOL satisfies strong unanimity: if all correct processes propose the same value, only that value can be decided. Whenever correct processes do not agree a priori (there is no unanimity), they may decide a default value ⊥ from COOL. Strong unanimity is, however, not sufficient for today’s state machine replication (SMR) and blockchain protocols. These systems value progress and require a decided value to always be valid (according to a predetermined predicate), excluding default decisions (such as ⊥) even in cases where there is no unanimity a priori. Validated Byzantine agreement satisfies this property (called external validity). Yet, the best error-free (or even signature-free) validated agreement solutions achieve only O(n2L) bit complexity, a far cry from the Ω(nL + n2) Dolev-Reischuk lower bound. Is it possible to bridge this complexity gap? We answer the question affirmatively. Namely, we present two new synchronous algorithms for validated Byzantine agreement, HashExt and ErrorFreeExt, with different trade-offs. Both algorithms are (1) signature-free, (2) optimally resilient (tolerate up to t < n/3 failures), and (3) early-stopping (terminate in O(f + 1) rounds, where f ≤ t denotes the actual number of failures). On the one hand, HashExt uses only hashes and achieves O(nL + n3κ) bit complexity, which is optimal for L ≥ n2κ (where κ is the size of a hash). On the other hand, ErrorFreeExt is error-free, using no cryptography whatsoever, and achieves O((nL + n2) log n) bit complexity, which is near-optimal for any L.

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Type
conference paper
DOI
10.4230/LIPIcs.DISC.2024.14
Scopus ID

2-s2.0-85208424207

Author(s)
Civit, Pierre  

École Polytechnique Fédérale de Lausanne

Dzulfikar, Muhammad Ayaz

National University of Singapore

Gilbert, Seth

National University of Singapore

Guerraoui, Rachid  

École Polytechnique Fédérale de Lausanne

Komatovic, Jovan  

École Polytechnique Fédérale de Lausanne

Vidigueira, Manuel  

École Polytechnique Fédérale de Lausanne

Zablotchi, Igor

Mysten Labs

Editors
Alistarh, Dan
Date Issued

2024-10-24

Publisher

Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing

Published in
Leibniz International Proceedings in Informatics, LIPIcs
ISBN of the book

9783959773522

Book part number

319

Article Number

14

Subjects

Bit complexity

•

Round complexity

•

Validated Byzantine agreement

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
DCL  
Event nameEvent acronymEvent placeEvent date
38 International Symposium on Distributed Computing

Madrid, Spain

2024-10-28 - 2024-11-01

FunderFunding(s)Grant NumberGrant URL

FNS

40B2-0_218648

MOE

200021_215383,MOE-T2EP20122-0014

Available on Infoscience
January 26, 2025
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/244835
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