Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Performing private database queries in a real-world environment using a quantum protocol

Philip Chan, I. Lucio-Martinez, Xiaofan Mo, Christoph Simon, Wolfgang Tittel

Published Jan 8, 2014• 43 citations
OpenAlex

Abstract

Private query protocols [1-3] use uncertainty in quantum mechanics to offer functionality similar to 1-out-of-N oblivious transfer (where a user, Ursula, retrieves a single element from a database provider, Dave, who learns nothing about which of the N elements was retrieved). The difference in functionality varies for each private query protocol, but in all cases is motivated by the fact that perfect 1-out-of-N oblivious transfer has been shown to be impossible if the attacker possess an arbitrarily powerful quantum computer [4]. Nonetheless, quantum protocols can offer security against stronger adversaries than protocols relying only on classical information, and it remains an interesting question as to what level of security can be achieved using quantum information. We present a proof-of-principle demonstration of a novel private query protocol that is loss- and fault-tolerant, making it suitable for implementation in a real-world environment, and show that it offers excellent privacy against several quantum attacks [5]. This demonstration is performed over a deployed fibre link between the University of Calgary and SAIT Polytechnic using a slightly modified quantum key distribution (QKD) system [6]. Oblivious transfer (OT) is a well studied primitive in classical information theory, and protocols

Related papers

Performing private database queries in a real-world environment using a quantum protocol

Philip Chan, Itzel Lucio-Martinez, Xiaofan Mo +2 more

In the well-studied cryptographic primitive 1-out-of-N oblivious transfer, a user retrieves a single element from a database of size N without the database learning which element was retrieved. While it has previously been shown that a secure implementation of 1-out-of-N oblivious transfer is impossible against arbitrarily powerful adversaries, recent research has revealed an interesting class of private query protocols based on quantum mechanics in a cheat sensitive model. Specifically, a practical protocol does not need to guarantee that the database provider cannot learn what element was retrieved if doing so carries the risk of detection. The latter is sufficient motivation to keep a database provider honest. However, none of the previously proposed protocols could cope with noisy channels. Here we present a fault-tolerant private query protocol, in which the novel error correction procedure is integral to the security of the protocol. Furthermore, we present a proof-of-concept demonstration of the protocol over a deployed fibre.

arXiv:1303.0865•Scientific Reports•Jun 10, 2014•60 citations

Practical private database queries based on a quantum-key-distribution protocol

Markus Jakobi, Christoph Simon, Nicolas Gisin +4 more

Private queries allow a user, Alice, to learn an element of a database held by a provider, Bob, without revealing which element she is interested in, while limiting her information about the other elements. We propose to implement private queries based on a quantum-key-distribution protocol, with changes only in the classical postprocessing of the key. This approach makes our scheme both easy to implement and loss tolerant. While unconditionally secure private queries are known to be impossible, we argue that an interesting degree of security can be achieved by relying on fundamental physical principles instead of unverifiable security assumptions in order to protect both the user and the database. We think that the scope exists for such practical private queries to become another remarkable application of quantum information in the footsteps of quantum key distribution.

arXiv:1002.4360•Physical Review A•Feb 2, 2011•224 citations

Impossibility of quantum private queries

Esther Hänggi, Severin Winkler

Symmetric private information retrieval is a cryptographic task allowing a user to query a database and obtain exactly one entry without revealing to the owner of the database which element was accessed. The task is a variant of general two-party protocols called and is closely related to oblivious transfer. Under the name , quantum protocols have been proposed to solve this problem in a cheat-sensitive way: In such protocols, it is not impossible for dishonest participants to cheat, but they risk detection [Giovannetti , ]. We give an explicit attack against any cheat-sensitive symmetric private information retrieval protocol, showing that any protocol that is secure for the user cannot have nontrivial security guarantees for the owner of the database: The user is even able to retrieve the database.

arXiv:2501.12842•Physical Review Research•Apr 3, 2026•0 citations

Towards communication-efficient quantum oblivious key distribution

M. V. Panduranga Rao, Markus Jakobi

Symmetrically private information retrieval, a fundamental problem in the field of secure multiparty computation, is defined as follows: A database $D$ of $N$ bits held by Bob is queried by a user Alice who is interested in the bit ${D}_{b}$ in such a way that (1) Alice learns ${D}_{b}$ and only ${D}_{b}$ and (2) Bob does not learn anything about Alice's choice $b$. While solutions to this problem in the classical domain rely largely on unproven computational complexity theoretic assumptions, it is also known that perfect solutions that guarantee both database and user privacy are impossible in the quantum domain. Jakobi et al. [Phys. Rev. A 83, 022301 (2011)] proposed a protocol for oblivious transfer using well-known quantum key device (QKD) techniques to establish an oblivious key to solve this problem. Their solution provided a good degree of database and user privacy (using physical principles like the impossibility of perfectly distinguishing nonorthogonal quantum states and the impossibility of superluminal communication) while being loss-resistant and implementable with commercial QKD devices (due to the use of the Scarani-Acin-Ribordy-Gisin 2004 protocol). However, their quantum oblivious key distribution (QOKD) protocol requires a communication complexity of $O(N\mathrm{log}N)$. Since modern databases can be extremely large, it is important to reduce this communication as much as possible. In this paper, we first suggest a modification of their protocol wherein the number of qubits that need to be exchanged is reduced to $O(N)$. A subsequent generalization reduces the quantum communication complexity even further in such a way that only a few hundred qubits are needed to be transferred even for very large databases.

arXiv:1208.2501•Physical Review A•Jan 28, 2013•63 citations

Practical Quantum Private Query with Classical Participants

Min Xiao, Di-Fang Zhang

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 .

Chinese Physics Letters•Mar 1, 2019•5 citations

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

Yi‐Hua Zhou, Xuewei Bai, Lei-Lei Li +2 more

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.

Communications in Theoretical Physics•Jan 1, 2018•8 citations
Private query protocols [1-3] use uncertainty in quantum mechanics to offer functionality similar to 1-out-of-N oblivious transfer (where a user, Ursula, retrieves a single element from a database provider, Dave, who learns nothing about which of the N elements was retrieved). The difference in functionality varies for each private query protocol, but in all cases is motivated by the fact that perfect 1-out-of-N oblivious transfer has been shown to be impossible if the attacker possess an arbitrarily powerful quantum computer [4]. Nonetheless, quantum protocols can offer security against stronger adversaries than protocols relying only on classical information, and it remains an interesting question as to what level of security can be achieved using quantum information. We present a proof-of-principle demonstration of a novel private query protocol that is loss- and fault-tolerant, making it suitable for implementation in a real-world environment, and show that it offers excellent privacy against several quantum attacks [5]. This demonstration is performed over a deployed fibre link between the University of Calgary and SAIT Polytechnic using a slightly modified quantum key distribution (QKD) system [6]. Oblivious transfer (OT) is a well studied primitive in classical information theory, and protocols
In the well-studied cryptographic primitive 1-out-of-N oblivious transfer, a user retrieves a single element from a database of size N without the database learning which element was retrieved. While it has previously been shown that a secure implementation of 1-out-of-N oblivious transfer is impossible against arbitrarily powerful adversaries, recent research has revealed an interesting class of private query protocols based on quantum mechanics in a cheat sensitive model. Specifically, a practical protocol does not need to guarantee that the database provider cannot learn what element was retrieved if doing so carries the risk of detection. The latter is sufficient motivation to keep a database provider honest. However, none of the previously proposed protocols could cope with noisy channels. Here we present a fault-tolerant private query protocol, in which the novel error correction procedure is integral to the security of the protocol. Furthermore, we present a proof-of-concept demonstration of the protocol over a deployed fibre.
Private queries allow a user, Alice, to learn an element of a database held by a provider, Bob, without revealing which element she is interested in, while limiting her information about the other elements. We propose to implement private queries based on a quantum-key-distribution protocol, with changes only in the classical postprocessing of the key. This approach makes our scheme both easy to implement and loss tolerant. While unconditionally secure private queries are known to be impossible, we argue that an interesting degree of security can be achieved by relying on fundamental physical principles instead of unverifiable security assumptions in order to protect both the user and the database. We think that the scope exists for such practical private queries to become another remarkable application of quantum information in the footsteps of quantum key distribution.
Symmetric private information retrieval is a cryptographic task allowing a user to query a database and obtain exactly one entry without revealing to the owner of the database which element was accessed. The task is a variant of general two-party protocols called and is closely related to oblivious transfer. Under the name , quantum protocols have been proposed to solve this problem in a cheat-sensitive way: In such protocols, it is not impossible for dishonest participants to cheat, but they risk detection [Giovannetti , ]. We give an explicit attack against any cheat-sensitive symmetric private information retrieval protocol, showing that any protocol that is secure for the user cannot have nontrivial security guarantees for the owner of the database: The user is even able to retrieve the database.
Symmetrically private information retrieval, a fundamental problem in the field of secure multiparty computation, is defined as follows: A database DDD of NNN bits held by Bob is queried by a user Alice who is interested in the bit Db{D}_{b}Db​ in such a way that (1) Alice learns Db{D}_{b}Db​ and only Db{D}_{b}Db​ and (2) Bob does not learn anything about Alice's choice bbb. While solutions to this problem in the classical domain rely largely on unproven computational complexity theoretic assumptions, it is also known that perfect solutions that guarantee both database and user privacy are impossible in the quantum domain. Jakobi et al. [Phys. Rev. A 83, 022301 (2011)] proposed a protocol for oblivious transfer using well-known quantum key device (QKD) techniques to establish an oblivious key to solve this problem. Their solution provided a good degree of database and user privacy (using physical principles like the impossibility of perfectly distinguishing nonorthogonal quantum states and the impossibility of superluminal communication) while being loss-resistant and implementable with commercial QKD devices (due to the use of the Scarani-Acin-Ribordy-Gisin 2004 protocol). However, their quantum oblivious key distribution (QOKD) protocol requires a communication complexity of O(NlogN)O(N\mathrm{log}N)O(NlogN). Since modern databases can be extremely large, it is important to reduce this communication as much as possible. In this paper, we first suggest a modification of their protocol wherein the number of qubits that need to be exchanged is reduced to O(N)O(N)O(N). A subsequent generalization reduces the quantum communication complexity even further in such a way that only a few hundred qubits are needed to be transferred even for very large databases.
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 .
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.