Multi-parties Quantum Secure Direct Communication with Authentication

In this chapter, a generalized architecture of quantum secure direct communication for N disjoint users with partial and full cooperation of quantum server is proposed. So, $$ N - 1 $$ disjointed users $$ u_{1},\, u_{2},\, \ldots,\, u_{N - 1} $$ can transmit a secret message of classical bits to a remote user $$ u_{N} $$ by utilizing the property of dense coding and Pauli unitary transformations. The authentication process between the quantum server and users validated by $$ EPR $$ entangled pair and $$ CNOT $$ gate. Afterward, the remaining $$ EPR $$ will be intended for generating shared $$ GHZ $$ states which used for directly transmitting the secret message. The partial cooperation process involved that $$ N - 1 $$ users can transmit a secret message directly to a remote user $$ u_{N} $$ through quantum channel. Furthermore, $$ N - 1 $$ users and a remote user $$ u_{N} $$ can communicate without an established quantum channel among them by full cooperation process. The security analysis of authentication and communication processes against many types of attacks proved that the attacker can’t gain any information during intercepting either authentication or communication processes. Hence, the security of transmitted message among $$ N $$ users is ensured as the attacker introducing an error probability irrespective of the sequence of measurement.