Quantum key distribution based on Greenberger-Horne-Zeilinger state
  An unsymmetrical quantum key distribution scheme is proposed, its security is guaranteed by the correlation of the Greenberger-Horne-Zeilinger triplet state. In the proposed protocol, the distribution of quantum states are unsymmetrical. This unsymmetrical characteristic makes the transmission qubits (except the loss qubits) be useful. Sequentially the proposed protocol has excellent efficiency and security which are very useful in the practical application. 
Guihua Zeng