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.     

A New Protocol for Quantum Private Query Against Joint-Measurement Attack

The quantum-key-distribution (QKD)-based quantum private query (QPQ) has become a research hotspot in recent years. Although such QPQ protocols are practical, joint-measurement (JM) attack is a noteworthy threat to the security of the database. In this paper, we propose a new QPQ protocol for enhancing database security against JM attack. The special procedure “receive→measure→re-prepare→send” for the user Alice prevents her from saving states to perform JM attack. Furthermore, since each photon only travels from one party to the other, our protocol reduces the drawback of two-way communication so that the transmission distance between Alice and the database holder Bob is satisfactory. We also analyze the security of the proposed protocol in terms of the database privacy and user privacy. Moreover, our protocol preserves the excellent character of QKD-based QPQs that it is loss tolerant.

     

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.     

Multi-Bit Quantum Private Query

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.     

Controlled Quantum Dialogue with Five-Qubit Entangled States

In this paper, a controlled quantum dialogue protocol is designed based on five-qubit entangled states. One five-qubit entangled state can be used to exchange one communicant’s two private bits with the other communicant’s two private bits under the control of an honest supervisor. Security analysis turns out that it can overcome the information leakage problem and can resist the active attacks from an outside attacker. The designed protocol only needs single-particle measurements and Bell state measurements, both of which can be realized with current technologies.

     

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.     

Multi-Bit Quantum Private Query

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.     

Secure quantum private query with real-time security check

As a class of one-sided two-party computation, unconditionally secure symmetrically private information retrieval (SPIR) is impossible. So the study of quantum symmetrically private information retrieval (QSPIR), i.e., quantum private query (QPQ) with an interesting degree of security is desirable. Known QPQ protocols [Phys. Rev. Lett. 100 (23) (2008) 230502; Phys. Rev. A 84 (2) (2011) 022313; Phys. Rev. A 83 (2011) 022301; Opt. Exp. 20 (16) (2012) 17411–17420] are claimed to be cheat-sensitive, especially not real-time. It is natural to ask whether we can design a QPQ protocol with real-time security check. In this paper, we introduce an untrusted third party and propose a framework of one-sided two-party quantum computation protocols with real-time security check. For clarity and without loss of generality, we demonstrate a concrete QPQ example under this framework by improving Gao et al's protocol [Opt. Exp. 20 (16) (2012) 17411–17420]. We discuss the security of the protocol and show that it really has real-time security check. The proposed framework paves the way for the design of one-sided two-party quantum computation protocols.     

Quantum private query: A new kind of practical quantum cryptographic protocol

This research aims to review the developments in the field of quantum private query(QPQ), a type of practical quantum cryptographic protocol. The primary protocol, as proposed by Jacobi et al., and the improvements in the protocol are introduced.Then, the advancements made in sability, theoretical security, and practical security are summarized. Additionally, we describe two new results concerning QPQ security. We emphasize that a procedure to detect outside adversaries is necessary for QPQ, as well as for other quantum secure computation protocols, and then briefly propose such a strategy. Furthermore, we show that the shift-and-addition or low-shift-and-addition technique can be used to obtain a secure real-world implementation of QPQ, where a weak coherent source is used instead of an ideal single-photon source.     

An Novel Protocol for the Quantum Secure Multi-Party Summation Based on Two-Particle Bell States

A protocol for the quantum secure multi-party summation based on two-particle Bell states is proposed. In this protocol, two-particle Bell states are used as private information carriers. Without using the entangled character of Bell states, we also use Pauli matrices operations to encode information and Hadamard matrix to extract information. The proposed protocol can also resist various attacks and overcomes the problem of information leakage with acceptable efficiency. In theory, our protocol can be used to build complex secure protocols for other multiparty computations and also lots of other important applications in distributed networks.     

An efficient Quantum Private Query Protocol Based on Oracle and Grover Iteration

Private query allows a client, Alice, to retrieve an item of a database hold by the server, Bob, without revealing which item he or she retrieved, while limiting his ability to access other items. In this paper, an efficient quantum private query (QPQ) protocol is proposed, where two oracle operations O_k, O_d are utilized to encode the encryption keys and the encrypted data items into their corresponding quantum superposition states \(\left | {\phi ^{\prime }} \right \rangle \), \(\left | {\psi ^{\prime }} \right \rangle \), and the Grover iteration is also introduced to extract the target state \(\left | {{d_{i}}^{\prime }} \right \rangle \) (i.e., the state of the encrypted data item Alice retrieved) from the superposition state. In order to guarantee the client’s privacy, the server Bob transmits all the encrypted data items of the database to the client Alice with oblivious transfer strategy. Compared with the previous qRAM-based or QKD-based QPQ protocols, our communication complexity (i.e., the number of transmitted qubits) is reduced from O(NlogN) or O(N) to O(logN), and the exchanged classical message is reduced from O(N) bits to O(logN) bits too. The security analysis shows our protocol can not only guarantee the server’s privacy but also the client’s privacy.

     

Secure Multi-Party Quantum Private Information Query

International Journal of Theoretical Physics - Different from the existing quantum key distribution (QKD)-based quantum private query (QPQ) protocols, we propose a secure multi-party quantum...     

Quantum private queries

We propose a cheat sensitive quantum protocol to perform a private search on a classical database which is efficient in terms of communication complexity. It allows a user to retrieve an item from the database provider without revealing which item he or she retrieved: if the provider tries to obtain information on the query, the person querying the database can find it out. The protocol ensures also perfect data privacy of the database: the information that the user can retrieve in a single query is bounded and does not depend on the size of the database. With respect to the known (quantum and classical) strategies for private information retrieval, our protocol displays an exponential reduction in communication complexity and in running-time computational complexity.     

Novel Multi-Party Quantum Key Agreement Protocol with G-Like States and Bell States

A significant aspect of quantum cryptography is quantum key agreement (QKA), which ensures the security of key agreement protocols by quantum information theory. The fairness of an absolute security multi-party quantum key agreement (MQKA) protocol demands that all participants can affect the protocol result equally so as to establish a shared key and that nobody can determine the shared key by himself/herself. We found that it is difficult for the existing multi-party quantum key agreement protocol to withstand the collusion attacks. Put differently, it is possible for several cooperated and untruthful participants to determine the final key without being detected. To address this issue, based on the entanglement swapping between G-like state and Bell states, a new multi-party quantum key agreement protocol is put forward. The proposed protocol makes full use of EPR pairs as quantum resources, and adopts Bell measurement and unitary operation to share a secret key. Besides, the proposed protocol is fair, secure and efficient without involving a third party quantum center. It demonstrates that the protocol is capable of protecting users’ privacy and meeting the requirement of fairness. Moreover, it is feasible to carry out the protocol with existing technologies.     

Robust High Capability QKD-Based Database Private Query

Quantum private query provides a contemporary solution to protect both user privacy and database security for the classical database administration and maintenance. A novel protocol of database private query based on high capability quantum key distribution is proposed, which examines if the inconsistent orthogonal basis usage and the error rate beyond the threshold for providing the high security among the key sender, carrier and verifier. The presented protocol could not only guarantees the query privacy and database security but also stand against the external eavesdropper.

     

Multi-Party Quantum Key Agreement by an Entangled Six-Qubit State

Since the first quantum key agreement protocol based on Bell state was presented by Zhou et al., much attention has focused on it, which is based on entangled states and product states. In this paper, we propose a multi-party quantum key agreement protocol, in which the genuinely maximally entangled six-qubit states are used. The presented protocol allows participants to share a secret key and preserves the following advantages. First, the outcome of the protocol is influenced by all parties; Second, the presented protocol is fairness, i.e., no one can determine the shared key alone; Third, outside eavesdroppers cannot gain the generated key without introducing any error. The security analysis shows that our protocol can resist both outside attacks and inside attacks.     

Same Initial States Attack in Yang et al.’s Quantum Private Comparison Protocol and the Improvement

In Yang et al.’s literatures (J. Phys. A: Math. 42, 055305, 2009; J. Phys. A: Math. 43, 209801, 2010), a quantum private comparison protocol based on Bell states and hash function is proposed, which aims to securely compare the equality of two participants’ information with the help of a dishonest third party (TP). However, this study will point out their protocol cannot resist a special kind of attack, TP’s same initial states attack, which is presented in this paper. That is, the dishonest TP can disturb the comparison result without being detected through preparing the same initial states. Finally, a simple improvement is given to avoid the attack.     

High-Efficiency Three-Party Quantum Key Agreement Protocol with Quantum Dense Coding and Bell States

We propose a high-efficiency three-party quantum key agreement protocol, by utilizing two-photon polarization-entangled Bell states and a few single-photon polarization states as the information carriers, and we use the quantum dense coding method to improve its efficiency. In this protocol, each participant performs one of four unitary operations to encode their sub-secret key on the passing photons which contain two parts, the first quantum qubits of Bell states and a small number of single-photon states. At the end of this protocol, based on very little information announced by other, all participants involved can deduce the same final shared key simultaneously. We analyze the security and the efficiency of this protocol, showing that it has a high efficiency and can resist both outside attacks and inside attacks. As a consequence, our protocol is a secure and efficient three-party quantum key agreement protocol.

     

Quantum federated learning through blind quantum computing

Private distributed learning studies the problem of how multiple distributed entities collaboratively train a shared deep network with their private data unrevealed. With the security provided by the protocols of blind quantum computation, the cooperation between quantum physics and machine learning may lead to unparalleled prospect for solving private distributed learning tasks.In this paper, we introduce a quantum protocol for distributed learning that is able to utilize the computational power of the remote quantum servers while keeping the private data safe. For concreteness, we first introduce a protocol for private single-party delegated training of variational quantum classifiers based on blind quantum computing and then extend this protocol to multiparty private distributed learning incorporated with diferential privacy. We carry out extensive numerical simulations with diferent real-life datasets and encoding strategies to benchmark the efectiveness of our protocol. We find that our protocol is robust to experimental imperfections and is secure under the gradient attack after the incorporation of diferential privacy. Our results show the potential for handling computationally expensive distributed learning tasks with privacy guarantees, thus providing a valuable guide for exploring quantum advantages from the security perspective in the field of machine learning with real-life applications.     

Quantum Protocol for Millionaire Problem

A quantum protocol for millionaire problem based on commutative encryption is proposed. In our protocol, Alice and Bob don’t have to use the entangled character, joint measurement of quantum states. They encrypt their private information and privately get the result of their private information with the help of a third party (TP). Correctness analysis shows that the proposed protocol can be used to get the result of their private information correctly. The proposed protocol can also resist various attacks and overcomes the problem of information leakage with acceptable efficiency. In theory, our protocol can be used to build complex secure protocols for other multiparty computation problems and also have lots of other important applications in distributed networks.