Improving the security of multiparty quantum secret sharing based on   entanglement swapping against participant attack
  In a recent paper [Z. J. Zhang and Z. X. Man, Phys. Rev. A 72, 022303(2005)], a multiparty quantum secret sharing protocol based on entanglement swapping was presented. However, as we show, this protocol is insecure in the sense that an unauthorized agent group can recover the secret from the dealer. Hence, we propose an improved version of this protocol which can stand against this kind of attack. 
Song Lin, Fei Gao, Fen-Zhuo Guo, Qiao-Yan Wen, Fu-Chen Zhu