Reexamining Security of Improved Multiparty Quantum Secret Splitting and Quantum State Sharing

In a recent letter [H.F. Wang, X. Ji, and S. Zhang, Phys. Lett. A 358 （2006） 11], an improvement of the multiparty quantum secret splitting and quantum state sharing protocol [F.G. Deng, et al., Phys. Lett. A 354 （2006） 190.] was presented. We study the security of the improved protocol and find that two or more dishonest participants may recover the secret from the dealer. Hence we further modify the improved protocol, which make it stand against this kind of attack.