Security Analysis and Improvements on a Semi-Quantum Electronic Voting Protocol

Recently, Qiu et al. proposed a semi-quantum voting scheme based on the ring signature (International Journal of Theoretical Physics, 60: 1550-1555(2021)), in which the signer and verifier only need to measure the received particles with Z-basis and perform some classical simple encryption/decryption operations on the classical message. Although their scheme is very efficient, it cannot resist the eavesdropping attacks and forgery attack. In this paper, first, the eavesdropping attacks on Qiu et al.'s scheme are proposed. Second, we show the forgery attack on their scheme. Then, based on the GHZ state, an improved semi-quantum electronic voting protocol is proposed. In the new protocol, the eavesdropping check technology not only can be used to detect the eavesdropping, but also can be used to share a random number. By using the random number and the shared key, the signed vote is encrypted so that it is infeasible for the adversary to trace the signer's identity and forge a valid signed vote. The new protocol overcomes all the security drawbacks of the old protocol. What is more, it has better practicability and efficiency than the similar semi-quantum voting protocols.