Abstract
We propose a new multiparty simultaneous quantum direct communication scheme based on Green–Horne–Zeilinger (GHZ) states and dense coding. For achieving high efficiency without leaking any information, four encoding schemes are prepared in advance. The present scheme has the capacity of transmitting (M + 1)M classical bits per group of M-particle GHZ states when there exist M parties. The technique of rearranging particles makes the legal users coequally exchange their messages in the same length. Both high efficiency and excellent security against the common attacks are virtues of this new scheme.