Semiquantum secure direct communication using EPR pairs

Quantum secure direct communication can transmit a secret message directly through quantum channels without first generating a shared secret key. In the most of the existing protocols, quantum secure direct communication is possible only when both communicating participants have quantum capabilities. So what happens if either party of two participants just has classical capabilities? In this paper, we propose a semiquantum secure direct communication protocol with Einstein–Podolsky–Rosen photon pairs in which the classical sender Bob transmits a secret message to quantum Alice directly. After checking the security of quantum channels, Bob encodes his secret message on Alice’s code sequence. Then, quantum Alice extracts Bob’s secret message by measuring her home qubits and the received code qubits, respectively. In addition, we demonstrate the security of the proposed protocol against some individual eavesdropping attacks. The efficiency analysis shows that our protocol can provide higher efficiency.