Abstract

The quantum private query (QPQ) is a quantum solution for the symmetrically private information retrieval problem. We study the security of quantum-key-distribution-based QPQ with weak coherent pulses. The result shows that multiphoton pulses have posed a serious threat to the participant's privacy in QPQ protocols.

Then we propose a decoy-state method that can help the honest participant detect the attack by exploiting multiphoton pulses and improving the key distillation process to defend against such attack. The analysis demonstrates that our decoy-state method significantly improves the security of the QPQ with weak coherent pulses, which solves a major obstacle in the practical application of the QPQ.