Efficient semi-direct three-party quantum secure exchange of information

We reconsider a recent publication [X.R. Jin, X. Ji, Y.Q. Zhang, S. Zhang, S.K. Hong, K.H. Yeon, C.I. Um, Phys. Lett. A 354 (2006) 67] on three-party quantum secure direct communication based on GHZ states and detect a drawback in it. We then modify it to be a valid protocol with the decoding rule worked out explicitly. Finally, we propose a way to double the efficiency of the modified protocol to economize the quantum resource.