Toward Optimal-Complexity Hash-Based Asynchronous MVBA with Optimal Resilience
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866916010513137664 |
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| author | Komatovic, Jovan Neu, Joachim Roughgarden, Tim |
| author_facet | Komatovic, Jovan Neu, Joachim Roughgarden, Tim |
| contents | Multi-valued validated Byzantine agreement (MVBA), a fundamental primitive of distributed computing, allows $n$ processes to agree on a valid $\ell$-bit value, despite $t$ faulty processes behaving maliciously. Among hash-based solutions for the asynchronous setting with adaptive faults, the state-of-the-art HMVBA protocol achieves optimal $O(n^2)$ message complexity, (near-)optimal $O(n \ell + n^2 λ\log n)$ bit complexity, and optimal $O(1)$ time complexity. However, it only tolerates $t < \frac15 n$ failures. In contrast, the best-known optimally-resilient protocol, SQ, incurs a higher bit complexity of $O(n^2 \ell + n^3 λ)$. This poses a fundamental question: Can a hash-based protocol be designed for the asynchronous setting with adaptive faults that simultaneously achieves optimal complexity and optimal resilience?
This paper takes a significant step toward answering this question. Namely, we introduce Reducer, an MVBA protocol that retains HMVBA's optimal complexity while improving its resilience to $t < \frac14 n$. Like HMVBA and SQ, Reducer relies exclusively on collision-resistant hash functions. A key innovation in Reducer's design is its internal use of strong multi-valued Byzantine agreement (SMBA), a new variant of Byzantine agreement we introduce and construct, which ensures that the decided value was proposed by a correct process. To further advance resilience toward the optimal one-third bound, we then propose Reducer++, an MVBA protocol that tolerates up to $t < (\frac13 - ε)n$ adaptive failures, for any fixed constant $ε> 0$. Unlike Reducer, Reducer++ does not rely on SMBA. Instead, it employs a novel approach involving hash functions modeled as random oracles to ensure termination. Reducer++ maintains constant time complexity, quadratic message complexity, and quasi-quadratic bit complexity, with constants dependent on $ε$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2410_12755 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Toward Optimal-Complexity Hash-Based Asynchronous MVBA with Optimal Resilience Komatovic, Jovan Neu, Joachim Roughgarden, Tim Distributed, Parallel, and Cluster Computing Multi-valued validated Byzantine agreement (MVBA), a fundamental primitive of distributed computing, allows $n$ processes to agree on a valid $\ell$-bit value, despite $t$ faulty processes behaving maliciously. Among hash-based solutions for the asynchronous setting with adaptive faults, the state-of-the-art HMVBA protocol achieves optimal $O(n^2)$ message complexity, (near-)optimal $O(n \ell + n^2 λ\log n)$ bit complexity, and optimal $O(1)$ time complexity. However, it only tolerates $t < \frac15 n$ failures. In contrast, the best-known optimally-resilient protocol, SQ, incurs a higher bit complexity of $O(n^2 \ell + n^3 λ)$. This poses a fundamental question: Can a hash-based protocol be designed for the asynchronous setting with adaptive faults that simultaneously achieves optimal complexity and optimal resilience? This paper takes a significant step toward answering this question. Namely, we introduce Reducer, an MVBA protocol that retains HMVBA's optimal complexity while improving its resilience to $t < \frac14 n$. Like HMVBA and SQ, Reducer relies exclusively on collision-resistant hash functions. A key innovation in Reducer's design is its internal use of strong multi-valued Byzantine agreement (SMBA), a new variant of Byzantine agreement we introduce and construct, which ensures that the decided value was proposed by a correct process. To further advance resilience toward the optimal one-third bound, we then propose Reducer++, an MVBA protocol that tolerates up to $t < (\frac13 - ε)n$ adaptive failures, for any fixed constant $ε> 0$. Unlike Reducer, Reducer++ does not rely on SMBA. Instead, it employs a novel approach involving hash functions modeled as random oracles to ensure termination. Reducer++ maintains constant time complexity, quadratic message complexity, and quasi-quadratic bit complexity, with constants dependent on $ε$. |
| title | Toward Optimal-Complexity Hash-Based Asynchronous MVBA with Optimal Resilience |
| topic | Distributed, Parallel, and Cluster Computing |
| url | https://arxiv.org/abs/2410.12755 |