Quantum private comparison (QPC) allows at least two users to compare the equality of their secret information, for which the security is based on the properties of quantum mechanics. To improve the use of quantum resources and the efficiency of private comparison, a new QPC protocol based on GHZ-like states is proposed. The protocol adopts unitary operations to encode the secret information instead of performing quantum key distribution (QKD), which can reduce the amount of computation required to perform QKD and improve the utilization of quantum resources. The decoy photon technique used to detect channel eavesdropping ensures that the protocol is resistant to external attacks. The quantum efficiency of the protocol reaches 66%. Compared with many previous QPC schemes, the proposed protocol does not need to share a key and has advantages in quantum efficiency and quantum resources.

Privacy comparison is an important research topic in secure multi-party computing, widely used in e-commerce, secret ballots, and other fields. However, the development of quantum computing power poses a growing potential security threat to secure multi-party algorithms based on mathematically tricky problems, and most of the proposed quantum privacy comparison schemes could be more efficient. Therefore, based on the W-state, we offer a more efficient semi-quantum privacy comparison method. The security analysis shows that the scheme can resist third-party, measurement, and entanglement attacks. Compared with the previous work, the scheme significantly improves communication efficiency and has stronger practicability.

Based on the two-photon six-qubit hyperentangled Bell states and hyper-coding, a new high-capacity quantum privacy comparison (QPC) protocol is proposed to realize a high utilization of quantum resources. The protocol enables two particles of hyperentangled Bell states to compare the equality of 6 classical bits of secret information between two quantum users. The unitary operations are used to encode the secret information and achieve dense coding. In the proposed protocol, decoy photons and the quantum uncertainty principle are used to ensure transmission channel security and particle security. comparisons with other QPC protocols in terms of quantum resources and efficiency reveal that the proposed protocol has significant advantages in quantum efficiency.