The security analysis of a threshold proxy quantum signature scheme

In the YW threshold proxy quantum signature scheme proposed by Yang and Wen, it is found that the basic signature key is the same as the basic verification key, which means that the bitwise exclusive OR (XOR) of the t proxy signature keys is exactly the XOR of the t proxy verification keys. Therefore, the proxy signers can deny their signature and the specific verifiers can forge a legal signature. Furthermore, an attacker can obtain a legal threshold proxy signature for an arbitrary new message. These findings show that there are hidden security loopholes that should be carefully constructed in designing more efficent YW-scheme.