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| As a new model for signing both quantum and classical messages, the arbitrated quantum signature (AQS) protocols have recently attracted alot of attentions. In this paper, we analyze their security by discussing the receiver's forgery of the signature. Different from the previous analysis,we summarize an explicit formalization of the present AQS protocols and propose the necessary and sufficient conditions against the receiver's forgeryattack. Based on the conditions, it can be verified that the attempt to design an improved optimal encryption by modifying the encryption operators isuseless to prevent the receiver's forgery of the signature. Moreover, we study the security of AQS signed for classical messages, and find it is stillsusceptible to the receiver's forgery. Finally, we provide some assistant security strategies to recover the security and discuss several potentialsecurity problems of AQS in the further research. |
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| Keywords:quantum cryptograph; quantum signature; the forgery attack |
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