Cryptanalysis and Improvement of a Quantum Secret Sharing Protocol between Multiparty and Multiparty with Single Photons and Unitary Transformations

In a recent paper Chin. Phys. Lett 25(2008)1187, a quantum secret sharing scheme between multiparty and multiparty was presented. We show that the protocol is not secure because the last member in Alice's group can illegally obtain most secret messages without introducing any error. Finally, a possible way to avoid the security flaw is suggested.