Advanced semi-quantum secure direct communication protocol based on bell states against flip attack

This study proposes two advanced semi-quantum secure direct communication (SQSDC) protocols to address the security problems in Xie et al.’s SQSDC protocol, and further, briefly discusses those security problems. Xie et al. (Int J Theor Phys 57(6):1881–1887, 2018) proposed an SQSDC protocol based on Bell states. However, an eavesdropper can deliberately flip the secret messages sent through Xie et al.’s SQSDC protocol, and can launch a man-in-the-middle attack to obtain part of the secret messages, both without being detected. If not addressed, these security problems can cause the protocol to fail at delivering secret messages. Accordingly, the proposed SQSDC protocols are resistant to the flip attack, man-in-the-middle attack, tagging attack, and collective attack. Moreover, the qubit efficiency of the proposed schemes is the same as Xie et al.’s scheme.