A generalized architecture of quantum secure direct communication for N   disjointed users with authentication
  In this paper, we generalize a secured direct communication process between N users with partial and full cooperation of quantum server. The security analysis of authentication and communication processes against many types of attacks proved that the attacker cannot gain any information during intercepting either authentication or communication processes. Hence, the security of transmitted message among N users is ensured as the attacker introduces an error probability irrespective of the sequence of measurement. 
Ahmed Farouk, Magdy Zakaria, Adel Megahed and Fatma A. Omara
cs.CR quant-ph