IACR News item: 22 March 2024
Hanwen Feng, Zhenliang Lu, Tiancheng Mai, Qiang Tang
ePrint Report
Multi-valued Validated Asynchronous Byzantine Agreement ($\mathsf{MVBA}$) is one essential primitive for many distributed protocols, such as asynchronous Byzantine fault-tolerant scenarios like atomic broadcast ($\mathsf{ABC}$), asynchronous distributed key generation, and many others. Recent surge of efforts have pushed the communication complexity of such protocols from $O(\ell n^2 + \lambda n^2 + n^3)$ (Cachin et al, CRYPTO'00), to $O(\ell n^2 + \lambda n^2)$ (Abbraham et al, PODC'19) and finally to optimal $O(\ell n + \lambda n^2)$ (Lu et al, PODC' 20), for $\ell$-bit inputs across a network of $n$ nodes, with security parameter $\lambda$.
However, those constructions of $\mathsf{MVBA}$ heavily rely on ``heavyweight'' cryptographic tools, such as non-interactive threshold signatures. The computational cost of algebraic operations, the susceptibility to quantum attacks, and the necessity of a trusted setup associated with threshold signatures present significant remaining challenges. There is a growing interest in information-theoretic or hash-based constructions (historically called signature-free constructions). Unfortunately, the state-of-the-art hash-based $\mathsf{MVBA}$ (Duan et al., CCS'23) incurs a large $O(\ell n^2 + \lambda n^3)$-bits communication, which in turn makes the hash-based $\mathsf{MVBA}$ inferior performance-wise comparing with the ``classical'' ones. Indeed, this was clearly demonstrated in our experimental evaluations.
To make hash-based $\mathsf{MVBA}$ actually realize its full potential, in this paper, we introduce an $\mathsf{MVBA}$ with adaptive security, and $\widetilde{O}(\ell n + \lambda n^2)$ communication, exclusively leveraging conventional hash functions. Our new $\mathsf{MVBA}$ achieves nearly optimal communication, devoid of heavy operations, surpassing both threshold signature-based schemes and the hash-based scheme in many practical settings, as demonstrated in our experiments. For example, in scenarios with a network size of $n = 201$ and an input size of $1.75$ MB, our $\mathsf{MVBA}$ exhibits a latency that is 81\% lower than that of the existing hash-based $\mathsf{MVBA}$ and 47\% lower than the threshold signature-based $\mathsf{MVBA}$. Our new construction also achieves optimal parameters in other metrics such as $O(1)$ rounds and $O(n^2)$ message complexity, except with a sub-optimal resilience, tolerating up to $20\%$ Byzantine corruptions (instead of $33\%$). Given its practical performance advantages, our new hash-based $\mathsf{MVBA}$ naturally leads to better asynchronous distributed protocols, by simply plugging it into existing frameworks.
However, those constructions of $\mathsf{MVBA}$ heavily rely on ``heavyweight'' cryptographic tools, such as non-interactive threshold signatures. The computational cost of algebraic operations, the susceptibility to quantum attacks, and the necessity of a trusted setup associated with threshold signatures present significant remaining challenges. There is a growing interest in information-theoretic or hash-based constructions (historically called signature-free constructions). Unfortunately, the state-of-the-art hash-based $\mathsf{MVBA}$ (Duan et al., CCS'23) incurs a large $O(\ell n^2 + \lambda n^3)$-bits communication, which in turn makes the hash-based $\mathsf{MVBA}$ inferior performance-wise comparing with the ``classical'' ones. Indeed, this was clearly demonstrated in our experimental evaluations.
To make hash-based $\mathsf{MVBA}$ actually realize its full potential, in this paper, we introduce an $\mathsf{MVBA}$ with adaptive security, and $\widetilde{O}(\ell n + \lambda n^2)$ communication, exclusively leveraging conventional hash functions. Our new $\mathsf{MVBA}$ achieves nearly optimal communication, devoid of heavy operations, surpassing both threshold signature-based schemes and the hash-based scheme in many practical settings, as demonstrated in our experiments. For example, in scenarios with a network size of $n = 201$ and an input size of $1.75$ MB, our $\mathsf{MVBA}$ exhibits a latency that is 81\% lower than that of the existing hash-based $\mathsf{MVBA}$ and 47\% lower than the threshold signature-based $\mathsf{MVBA}$. Our new construction also achieves optimal parameters in other metrics such as $O(1)$ rounds and $O(n^2)$ message complexity, except with a sub-optimal resilience, tolerating up to $20\%$ Byzantine corruptions (instead of $33\%$). Given its practical performance advantages, our new hash-based $\mathsf{MVBA}$ naturally leads to better asynchronous distributed protocols, by simply plugging it into existing frameworks.
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