Robust Multiparty Quantum Secret Sharing against Participant ForcibleManipulation

The security of the multiparty quantum secret sharing protocol proposed by Gao [G. Gao, Commun. Theor. Phys. 52 (2009) 421] isanalyzed. It is shown that this protocol is vulnerable since theagents' imperfect encryption scheme can be attacked by a powerfulparticipant. We introduce a attack strategy called participant forcible manipulation and analyze the information leakage in this protocol under this attack. At last, we give an improved version of the original protocol. The improved protocol is robust and has the same efficiency as the original one.