Threshold quantum secret sharing between multiparty and multiparty using Greenberger-Horne-Zeilinger state

We propose a (t, m)-(s, n) threshold quantum secret sharing protocol between multiparty (m members in group 1) and multiparty (n members in group 2) using a sequence of Greenberger-Horne-Zeilinger (GHZ) states, which is useful and efficient when the parties of communication are not all present. In the protocol, Alice prepares a sequence of GHZ states in one of the eight different states and sends the last two particles to the first agent while other members encode their information on the sequence via unitary transformations. Finally the last member in group 2 measures the qubits. It is shown that this scheme is safe.