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Advanced Quantum Technologies

Quantum‐Key‐Distribution‐Based Quantum Private Query with Phase Encoding

Bin Liu, Xingyu Li, Bei Gong, Nankun Mu, Wei Huang

Published Nov 11, 2025• 3 citations
Publisher

Abstract

ABSTRACT Quantum private query (QPQ) as the quantum version of the symmetrically private information retrieval problem, is recognized as a new quantum cryptographic protocol with great practical potential. Compared to classical schemes, QPQ protocols provide higher security and lower complexity. However, most of the existing protocols are polarization encoding ones, which are incompatible with current optical fiber communication quantum networks. Moreover, the high demands for quantum capabilities and the scarcity of affordable quantum resources present challenges. This paper proposes a QPQ protocol with phase encoding of two‐way communication, enhancing the stability and reducing quantum resources expenditure. The security analysis demonstrates that this protocol is capable of effectively resisting several common attacks, safeguarding the privacy security of the database and user. Furthermore, the protocol has the potential to be implemented in existing phase‐encoding quantum systems, promoting progress in the practical application of QPQ.

DOI
10.1002/qute.202500471

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ABSTRACT Quantum private query (QPQ) as the quantum version of the symmetrically private information retrieval problem, is recognized as a new quantum cryptographic protocol with great practical potential. Compared to classical schemes, QPQ protocols provide higher security and lower complexity. However, most of the existing protocols are polarization encoding ones, which are incompatible with current optical fiber communication quantum networks. Moreover, the high demands for quantum capabilities and the scarcity of affordable quantum resources present challenges. This paper proposes a QPQ protocol with phase encoding of two‐way communication, enhancing the stability and reducing quantum resources expenditure. The security analysis demonstrates that this protocol is capable of effectively resisting several common attacks, safeguarding the privacy security of the database and user. Furthermore, the protocol has the potential to be implemented in existing phase‐encoding quantum systems, promoting progress in the practical application of QPQ.
Abstract 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.
We propose a quantum solution to the classical private information retrieval (PIR) problem, which allows one to query a database in a private manner. The protocol offers privacy thresholds and allows the user to obtain information from a database in a way that offers the potential adversary, in this model the database owner, no possibility of deterministically establishing the query contents. This protocol may also be viewed as a solution to the symmetrically private information retrieval problem in that it can offer database security (inability for a querying user to steal its contents). Compared to classical solutions, the protocol offers substantial improvement in terms of communication complexity. In comparison with the recent quantum private queries [Phys. Rev. Lett. 100, 230502 (2008)] protocol, it is more efficient in terms of communication complexity and the number of rounds, while offering a clear privacy parameter. We discuss the security of the protocol and analyze its strengths and conclude that using this technique makes it challenging to obtain the unconditional (in the information-theoretic sense) privacy degree; nevertheless, in addition to being simple, the protocol still offers a privacy level. The oracle used in the protocol is inspired both by the classical computational PIR solutions as well as the Deutsch-Jozsa oracle.
Abstract Most of the existing Quantum Private Queries (QPQ) protocols provide only single-bit queries service, thus have to be repeated several times when more bits are retrieved. Wei et al.'s scheme for block queries requires a high-dimension quantum key distribution system to sustain, which is still restricted in the laboratory. Here, based on Markus Jakobi et al.'s single-bit QPQ protocol, we propose a multi-bit quantum private query protocol, in which the user can get access to several bits within one single query. We also extend the proposed protocol to block queries, using a binary matrix to guard database security. Analysis in this paper shows that our protocol has better communication complexity, implementability and can achieve a considerable level of security.
Quantum Private Query (QPQ) based on Quantum Key Distribution (QKD) is among the most practically viable quantum communication protocols, with application value second only to QKD itself. However, prevalent security vulnerabilities in the post-processing stages of most existing QKD-based QPQ protocols have been severely overlooked. This study focuses on hidden information extraction under undetermined signal bits, revealing that most such QPQ protocols face severe security threats even without complex quantum resources. Specifically, direct observation attack causes incremental information leakage, while the minimum error discrimination attack efficiently steals additional database inforamtion. To address these critical flaws, the proposed multi-encryption defense scheme is compatible with existing QPQ protocols. The study demonstrates the necessity of the multi-encryption strategy for the security of databases in QPQ, providing key theoretical and technical support for constructing practical QPQ protocols resistant to real-world attacks.
Quantum key distribution (QKD)-based quantum private query (QPQ) is a practical application of QKD, which relaxes the security condition of perfectly concealing a private query to a cheating-sensitive strategy. We propose a QPQ protocol based on the delegated QKD scheme (DQKD-based QPQ), in which two almost 'classical' clients (data user and database owner) can establish a 1-out-of-N oblivious key with the help of a cloud server with full quantum ability. Concretely, the two classical participants in the DQKD-based QPQ only need to access the quantum channel and reorder qubits, and the costly quantum operations, quantum state preparation and measurement are outsourced to a full quantum server in the cloud without leaking participants' privacy. The proposed protocol not only provides a cloud-based framework of QKD-based QPQ, but also obtains better security by a real-time security check, which can protect the security of the database and user against all potential attacks even if the quantum server is assumed to be a powerfully untrusted adversary .