Improving the security of multiparty quantum secret sharing against Trojan horse attack

摘要

Security of the multiparty quantum secret sharing (MQSS) protocol recently proposed by Zhang et al. [Phys. Rev. A \textbf{71}, 044301 (2005)] is analyzed in the case that the agent who prepares the quantum signal, say Bob wants to eavesdrop the information about the unitary operations done by the other agent, Charlie by using a Trojan horse attack. Bob can replace the single-photon signal with a multi-photon one and Charlie cannot find this cheating as she does not measure the photons before they runs back from the boss Alice, which reveals that this MQSS protocol is not secure. Finally, we present a possible improvement of the MQSS protocol security with two single-photon measurements and four unitary operations.