Efficient and secure semi-quantum secure direct communication protocol against double CNOT attack

In 2019, Sun et al. (Mod Phys Lett A 34:1950004, 2019) proposed two semi-quantum secure direct communication (SQSDC) protocols using Bell states. However, an eavesdropper can launch a doubleCNOTattack to reveal or steal the sender's secret message, without being detected. In addition, the SQSDC protocol of Sun et al. suffers severely from information leakage problem. If these security issues are not addressed, the SQSDC protocol may fail at delivering secret messages. Thus, this study proposes an efficient and secure SQSDC protocol to circumvent these problems. The analyses results demonstrated that the proposed SQSDC protocol can effectively avoid the double CNOT attack, information leakage problem and other popular attacks.