Comment and improvement on the “semi-quantum ring signature protocol based on multi-particle GHZ state”

Recently, a novel semi-quantum ring signature protocol (Quantum Inf. Process., 22(9), 337(2023)) was proposed. Although it has the properties of semi-quantum protocol, its verification process will fail when more than two users take part in the signature protocol. We show an example, in which four participants including the trusted third-party Trent are used, to prove the signature cannot be verified. Then, an improved semi-quantum ring signature protocol is proposed. In the new ring signature protocol, Trent generates the shared keys with each ring user. According to the shared keys, Trent encodes the GHZ state such that the identity of the true ring signatory can be traced by Trent. What is more, in our protocol, by measuring the received particles, all the ring users can create the same session key to generate a ring signature, which can guarantee the anonymity of the voter in the protocol. The improved ring signature protocol overcomes the drawback of the old one and can be secure against various eavesdropping attacks and forgery attack. Compared with the similar quantum ring signature protocols, ours has better practicability and efficiency.