Secure Direct Communication Based on Secret Transmitting Order of   Particles
  We propose the schemes of quantum secure direct communication (QSDC) based on secret transmitting order of particles. In these protocols, the secret transmitting order of particles ensures the security of communication, and no secret messages are leaked even if the communication is interrupted for security. This strategy of security for communication is also generalized to quantum dialogue. It not only ensures the unconditional security but also improves the efficiency of communication. 
Ai-Dong Zhu, Yan Xia, Qiu-Bo Fan, Shou Zhang