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Quantum Information Processing

Semi-honest mediated cross-domain quantum key distribution using GHZ-like states

Chaonan Wang, Mengyan Li, Yanlin Zhang, Wei Gao

Published May 4, 2026• 0 citations
Publisher

Abstract

Abstract As quantum communication networks approach practical deployment, mediated semi-quantum key distribution (MSQKD) has attracted attention for enabling classical users to share keys via semi-honest servers. This paper proposes a cross-domain MSQKD protocol based on four-particle GHZ-like states. Two semi-honest servers prepare and transmit quantum sequences with decoy states, while users perform only Bell and single-photon measurements to derive shared keys. The protocol eliminates additional unitary operations, significantly reducing user-side quantum requirements, hardware costs, and implementation complexity. By exploiting entanglement correlations, it achieves a qubit efficiency of 42.86% and resists both external and internal attacks. The feasibility of the protocol is verified through simulations on Qiskit and the IBM quantum platform, demonstrating its practicality under current quantum technology.

DOI
10.1007/s11128-026-05173-6

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Abstract As quantum communication networks approach practical deployment, mediated semi-quantum key distribution (MSQKD) has attracted attention for enabling classical users to share keys via semi-honest servers. This paper proposes a cross-domain MSQKD protocol based on four-particle GHZ-like states. Two semi-honest servers prepare and transmit quantum sequences with decoy states, while users perform only Bell and single-photon measurements to derive shared keys. The protocol eliminates additional unitary operations, significantly reducing user-side quantum requirements, hardware costs, and implementation complexity. By exploiting entanglement correlations, it achieves a qubit efficiency of 42.86% and resists both external and internal attacks. The feasibility of the protocol is verified through simulations on Qiskit and the IBM quantum platform, demonstrating its practicality under current quantum technology.
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In this paper, we propose a new efficient mediated semi-quantum key distribution (MSQKD) protocol, facilitating the establishment of a shared secret key between two classical participants with the assistance of an untrusted third party (TP). Unlike existing MSQKD protocols, our approach significantly reduces the quantum requirements for TP, who only needs to prepare and measure qubits in the XXX basis. Meanwhile, the classical participants are limited to preparing and measuring qubits in the ZZZ basis, along with performing Hadamard operations. This reduction in quantum overhead enhances the practicality of our MSQKD protocol without compromising qubit efficiency. Additionally, we demonstrate the security of our protocol against various well-known attacks.
The mediated semi-quantum key distribution (MSQKD) protocol is an important research issue that lets two classical participants share secret keys securely between each other with the help of a third party (TP). However, in the existing MSQKD protocols, there are two improvable issues, namely (1) the classical participants must be equipped with expensive detectors to avoid Trojan horse attacks and (2) the trustworthiness level of TP must be honest. To the best of our knowledge, none of the existing MSQKD protocols can resolve both these issues. Therefore, this study takes Bell states as the quantum resource to propose a MSQKD protocol, in which the classical participants do not need a Trojan horse detector and the TP is dishonest. Furthermore, the proposed protocol is shown to be secure against well-known attacks and the classical participants only need two quantum capabilities. Therefore, in comparison to the existing MSQKD protocols, the proposed protocol is better practical.
Abstract Mediated semi-quantum key distribution (MSQKD) is a popular topic in quantum cryptography, which requires less quantum abilities from legitimate users, Alice and Bob, and has the advantage of high noise tolerance. In this paper, we propose a new MSQKD protocol where the third-party quantum server M can randomly send single-state and entangled-state without informing Alice and Bob of the type of qubit. In addition, in the case where M has an infinite quantum source, we derive the key rate and noise tolerance of the protocol, which proves the unconditional security of the protocol. Furthermore, as M changes the ratio of single-state and entangled-state, the noise tolerance also changes. In particular, when M sends only single-state or entangled-state, our protocol degenerates into the previous MSQKD protocols, and we derive a higher noise tolerance by analysing the mismatch terms.
Classical users can share a secret key with a quantum user by using a semi-quantum key distribution (SQKD) protocol. Allowing two classical users to share a secret key is the objective of the mediated semi-quantum key distribution (MSQKD) protocol. However, the existing MSQKD protocols need a quantum user to assist two classical users in distributing the secret keys, and these protocols require that the classical users be equipped with a Trojan horse photon detector. This reduces the practicability of the MSQKD protocols. Therefore, in this study we propose a lightweight MSQKD, in which the two participants and third party are classical users. Due to the usage of the one-way transmission strategy, the proposed lightweight MSQKD protocol is free from quantum Trojan horse attack. The proposed MSQKD is more practical than the existing MSQKD protocols.
Abstract In this paper, we propose an efficient lightweight mediated semi-quantum key distribution (LM-SQKD) protocol, which enables two lightweight participants to securely establish a shared key with the help of an untrusted third party (TP). Compared with existing M-SQKD protocols, our protocol significantly reduces the overall quantum burden and improves the qubit efficiency, where TP only needs to prepare and measure qubits in the X basis and two lightweight participants are just required to execute three unitary operations and reflect qubits. Furthermore, the detailed security analysis verifies that the proposed protocol can against three well-known attacks.