Intercept-and-resend attack and improvement of semiquantum secure direct communication using EPR pairs

Zhang et al. (Quantum Inf Process 16:117, 2017. https://doi.org/10.1007/s11128-017-1573-3) proposed a semiquantum secure direct communication (SQSDC) using Einstein–Podolsky–Rosen pairs. However, as shown in this study, an eavesdropper can reveal the sender’s secret message by performing an intercept-and-resend attack. Furthermore, an eavesdropper can also launch a modification attack to modify the sender’s secret message without being detected. Without considering these security issues, the SQSDC protocol could fail at providing the secret message. Thus, an improvement is proposed to circumvent these problems and to improve the qubit efficiency from 10 to 17%.