Semiquantum secure direct communication with authentication based on single-photons

Semiquantum cryptography has drawn much attention in recent years since it simplifies the implementation of quantum cryptographic protocols. In this paper, we study semiquantum secure direct communication (SQSDC). Based on single-photons, we propose a two-step SQSDC protocol with identity authentication, which can be used to prevent impersonation and the man-in-the-middle attack. Different from previous protocols based on quantum entanglement or quantum memory, our protocol removes there restrictions for simplifying its physical implementation. We prove that our two-step SQSDC protocol is completely robust. That is, any adversarial attempting to learn some information on the secure message or identity strings will inevitably induce some errors that can be detected by communicators.