Improvement of Security of Three-Party Quantum Secure Direct Communication Based on GHZ States

A protocol for three-party quantum secure direct communication based on Greenberger--Horne--Zeilinger (GHZ) states was recently proposed by Jin it et al. Phys. Lett. A 354(2006)67 By analysing the protocol we find some security loopholes, e.g. one bit of secret messages of a party (Alice in the original paper) can always be leaked straight to the public without any eavesdropping. These problems suggested previously are discussed and possible solutions are presented to improve the security of the original protocol.