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