Controlled Quantum Secure Direct Communication Protocol Based on Extended Three-particle GHZ State Decoy

Extended three-particle GHZ state decoy is introduced in controlled quantum secure direct communication to improve eavesdropping detection probability and prevent correlation-elicitation (CE) attack. Each particle of extended three-particle GHZ state decoy is inserted into sending particles to detect eavesdroppers, which reaches 63% eavesdropping detection probability. And decoy particles prevent the receiver from obtaining the correct correlation between particle 1 and particle 2 before the sender coding on them, so that he can not get any secret information without the controller's permission. In the security analysis, the maximum amount of information that a qubit contains is obtained by introducing the entropy theory method, and two decoy strategies are compared quantitatively. If the eavesdroppers intend to eavesdrop on secret information, the per qubit detection rate of using only two particles of extended three-particle GHZ state as decoy is 58%; while the presented protocol using three particles of extended three-particle GHZ state as decoy reaches per qubit 63%.