A new controlled quantum secure direct communication protocol based on a four-qubit cluster state

A new controlled quantum secure direct communication (CQSDC) protocol is presented by using a four-particle cluster state as quantum channel and the physical characteristics of controlled quantum teleportation to implement the transmission and the control. In this scheme, the receiver can receive the secret message from the sender and recover the secret message under the permission of the controller. According to the security analysis, the communication is secure against both participant and outside attacks, so this CQSDC protocol is secure and feasible.