Beating the fault-tolerance bound and security loopholes for Byzantine agreement with a quantum solution

• Published in: arXiv.org 2023-11
• Main Authors: Chen-Xun, Weng, Rui-Qi, Gao, Yu, Bao, Bing-Hong, Li, Wen-Bo, Liu, Yuan-Mei, Xie, Yu-Shuo Lu, Hua-Lei, Yin, Zeng-Bing, Chen
• Format: Article
• Language: English
• Subjects: Agreements; Blockchain; Cryptography; Digital signatures; Fault tolerance; Nodes; Security
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2206.09159

Byzantine agreement, the underlying core of blockchain, aims to make every node in a decentralized network reach consensus. Classical Byzantine agreements unavoidably face two major problems. One is \(1/3\) fault-tolerance bound, which means that the system to tolerate \(f\) malicious players requires at least \(3f+1\) players. The other is the security loopholes from its classical cryptography methods. Here, we propose a Byzantine agreement framework with unconditional security to break this bound with nearly \(1/2\) fault tolerance due to multiparty correlation provided by quantum digital signatures. \textcolor{black}{It is intriguing that quantum entanglement is not necessary to break the \(1/3\) fault-tolerance bound, and we show that weaker correlation, such as asymmetric relationship of quantum digital signature, can also work.} Our work strictly obeys two Byzantine conditions and can be extended to any number of players without requirements for multiparticle entanglement. We experimentally demonstrate three-party and five-party consensus for a digital ledger. Our work indicates the quantum advantage in terms of consensus problems and suggests an important avenue for quantum blockchain and quantum consensus networks.