Quantum secret sharing protocol between multiparty and multiparty with   single photons and unitary transformations
  We propose a scheme of quantum secret sharing between Alices' group and Bobs' group with single photons and unitary transformations. In the protocol, one member in Alices' group prepares a sequence of single photons in one of four different states, while other members directly encode their information on the sequence of single photons via unitary operations, after that the last member sends the sequence of single photons to Bobs' group. Then Bobs except for the last one do work similarly. Finally last member in Bobs' group measures the qubits. If Alices and Bobs guarnnted the security of quantum channel by some tests, then the qubit states sent by last member of Alices' group can be used as key bits for secret sharing. It is shown that this scheme is safe. 
Feng-Li Yan, Ting Gao, You-Cheng Li