The Security Problems in Some Novel Arbitrated Quantum Signature Protocols

With the development of quantum signature, two improved arbitrated quantum signature(AQS) protocols have been presented with different quantum encryptions. In this paper, some security loopholes during the two AQS protocols are proposed. In the enhanced arbitrated quantum signature(EAQS) protocol, though the signer is not able to deny his signature, the receiver can still forge some valid signatures. In the chaos-based arbitrated quantum signature(CAQS) protocol, the receiver can forge a valid signature without being caught, and the signer can also deny her signature after the signing phase. Finally, some potential improved ideas are discussed.