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Cryptanalysis of Controlled Bidirectional Quantum Secure Direct Communication Network Using Classical XOR Operation and Quantum Entanglement

In a recent letter, a controlled bidirectional quantum secure direct communication protocol with cluster states was proposed. We analyzed the security of this protocol and found that it is insecure. In the original protocol, a dishonest controller can eavesdrop the secret messages exchanged between the users, and a dishonest user may achieve his communication goal without the permission of the controller. The corresponding two kinds of attack strategies are presented. Finally, we give a feasible improvement of this communication protocol.