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Eavesdropping on quantum secure direct communication with W state in noisy channel. (English) Zbl 1392.81080

Summary: Security of the quantum secure direct communication protocol (i.e., the C-S QSDC protocol) recently proposed by H.-J. Cao and H.-S. Song [“Quantum secure direct communication with W state”, Chin. Phys. Lett. 23, No. 2, 290–292 (2006; doi:10.1088/0256-307X/23/2/005)] is analyzed in the case of considerable quantum channel noise. The eavesdropping scheme is presented, which reveals that the C-S QSDC protocol is not secure if the quantum bit error rate (QBER) caused by quantum channel noise is higher than 4.17%. Our eavesdropping scheme induces about 4.17% QBER for those check qubits. However, such QBER can be hidden in the counterpart induced by the noisy quantum channel if the eavesdropper Eve replaces the original noisy channel by an ideal one. Furthermore, if the QBER induced by quantum channel noise is lower than 4.17%, then in the eavesdropping scheme Eve still can eavesdrop part of the secret messages by safely attacking a fraction of the transmitted qubits. Finally, an improvement on the C-S QSDC protocol is put forward.

MSC:

81P45 Quantum information, communication, networks (quantum-theoretic aspects)
81P94 Quantum cryptography (quantum-theoretic aspects)
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