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arXiv:quant-ph/0405167 · Physical Review A

Byzantine agreement with two quantum-key-distribution setups

S. Iblisdir, Nicolas Gisin

Published Sep 29, 2004• 22 citations
arXivHTMLPDF

Abstract

It is pointed out that two separated quantum channels and three classical authenticated channels are sufficient resources to achieve detectable broadcast.
DOI
10.1103/physreva.70.034306

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We design and experimentally validate quantum circuits that prepare a quantum resource state which, when combined with authenticated classical communication, enables a protocol for detectable Byzantine broadcast and detectable Byzantine consensus. For the broadcast version of the problem, we propose an efficient leader-follower quantum circuit that prepares this resource state with depth O(logn), using O(n) two-qubit gates and O(n) ancillary qubits. We also develop a majority-based leader-selection scheme, for the consensus version of the problem; the scheme is based on the same leaderfollower quantum circuit and on coherent Hamming-weight computation, which prepares a fictitious leader qubit directly from any initial network state specified by the participant parties. The resulting fictitious leader state is then used as input to the leader-follower circuit to prepare a resource state consistent with majority voting on a common basis, thereby enabling detectable Byzantine consensus. In particular, we prove that, when supplemented with authenticated classical channels for the communication of quantum measurement outputs, the resulting protocols achieve detectable Byzantine broadcast and detectable Byzantine consensus, respectively. Under correct operation, all correct parties output the same value, namely the leader's value or the majority value. In the presence of Byzantine parties or quantum circuit deviations, all correct parties detect the inconsistency and abort. Furthermore, we demonstrate the feasibility of the approach through a proofof-principle implementation on an IBM quantum processor.
Distributed systems -- spanning cloud computing, edge networks, and federated databases -- rely on classical cryptographic channels whose security rests on computational hardness assumptions increasingly threatened by advances in quantum computing. Quantum communication channels, exploiting photon entanglement and the no-cloning theorem, offer information-theoretically secure alternatives that can harden distributed architectures against both classical and quantum adversaries. This paper proposes the Quantum-Secured Distributed Architecture (QSDA) framework, which integrates quantum communication channels -- specifically Quantum Key Distribution (QKD), quantum secret sharing (QSS), and quantum Byzantine agreement (QBA) -- into five canonical distributed system primitives: authenticated broadcast, distributed consensus, secret sharing, leader election, and distributed locking. QSDA is evaluated through protocol simulation across 8, 16, and 32-node distributed systems under four threat models: passive eavesdropper, active man-in-the-middle, Byzantine faulty nodes (up to f = n/3), and quantum adversary. Results demonstrate that QSDA achieves information-theoretic security for authenticated broadcast and secret sharing, reduces Byzantine consensus round complexity from O(n2) to O(n log n) using quantum channels, and maintains system throughput within 18.4% of classical baseline despite quantum channel overhead. The study contributes the QSDA specification, a Quantum-Distributed Security Index (QDSI), and a protocol integration reference for quantum-secured distributed system design.