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

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.