Improved Eavesdropping Detection Strategy Based on Extended Three-particle Greenberger-Horne-Zeilinger State in Two-step Quantum Direct Communication Protocol

In order to improve the eavesdropping detection efficiency in two-step quantum direct communication protocol, an improved eavesdropping detection strategy using extended three-particle GHZ state is proposed, in which extended three-particle GHZ state is used to detect eavesdroppers. During the security analysis, the method of the entropy theory is introduced, and two detection strategies are compared quantitatively by using the constraint between the information which eavesdropper can obtain and the interference introduced. If the eavesdroppers intend to obtain all information, the eavesdropping detection rate of the original two-step quantum direct communication protocol by using EPR pair block as detection particles is 50%; while the proposed strategy’s detection rate is 59%. In the end, the security of the proposed protocol is discussed. The analysis results show that the eavesdropping detection strategy presented is more secure.