QKD-based quantum private query without a failure probability

In this paper, we present a quantum-key-distribution(QKD)-based quantum private query(QPQ) protocol utilizing single-photon signal of multiple optical pulses. It maintains the advantages of the QKD-based QPQ, i.e., easy to implement and loss tolerant. In addition, different from the situations in the previous QKD-based QPQ protocols, in our protocol, the number of the items an honest user will obtain is always one and the failure probability is always zero. This characteristic not only improves the stability(in the sense that, ignoring the noise and the attack, the protocol would always succeed), but also benefits the privacy of the database(since the database will no more reveal additional secrets to the honest users). Furthermore, for the user's privacy, the proposed protocol is cheat sensitive, and for security of the database, we obtain an upper bound for the leaked information of the database in theory.

Decoy-state method for quantum-key-distribution-based quantum private query

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.

Robust QKD-based private database queries based on alternative sequences of single-qubit measurements

Quantum channel noise may cause the user to obtain a wrong answer and thus misunderstand the database holder for existing QKD-based quantum private query(QPQ) protocols. In addition, an outside attacker may conceal his attack by exploiting the channel noise. We propose a new, robust QPQ protocol based on four-qubit decoherence-free(DF) states. In contrast to existing QPQ protocols against channel noise, only an alternative fixed sequence of single-qubit measurements is needed by the user(Alice) to measure the received DF states. This property makes it easy to implement the proposed protocol by exploiting current technologies. Moreover, to retain the advantage of flexible database queries, we reconstruct Alice's measurement operators so that Alice needs only conditioned sequences of single-qubit measurements.

A Quantum Private Query Protocol for Enhancing both User and Database Privacy

In order to protect the privacy of query user and database,some QKD-based quantum private query(QPQ)protocols were proposed.Unfortunately some of them cannot resist internal attack from database perfectly;some others can ensure better user privacy but require a reduction of database privacy.In this paper,a novel two-way QPQ protocol is proposed to ensure the privacy of both sides of communication.In our protocol,user makes initial quantum states and derives the key bit by comparing initial quantum state and outcome state returned from database by ctrl or shift mode instead of announcing two non-orthogonal qubits as others which may leak part secret information.In this way,not only the privacy of database be ensured but also user privacy is strengthened.Furthermore,our protocol can also realize the security of loss-tolerance,cheat-sensitive,and resisting JM attack etc.