arXiv subjects

Guang Ping He

Publications and source records attributed to Guang Ping He.

At least 37 records · Page 2Linked to original sources

arXiv2016

Quantum private comparison protocol without a third party

To evade the well-known impossibility of unconditionally secure quantum two-party computations, previous quantum private comparison protocols have to adopt a third party. Here we study how far we can go with two parties only. We propose a very feasible and efficient protocol. Intriguingly, although the average amount of information leaked cannot be made arbitrarily small, we find that it never exceeds 14 bits for any length of the bit-string being compared.

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arXiv2015

Secure quantum weak oblivious transfer against individual measurements

In quantum weak oblivious transfer, Alice sends Bob two bits and Bob can learn one of the bits at his choice. It was found that the security of such a protocol is bounded by $2P_{Alice}^{\ast }+P_{Bob}^{\ast }\geq 2$, where $P_{Alice}^{\ast }$ is the probability with which Alice can guess Bob's choice, and $P_{Bob}^{\ast }$ is the probability with which Bob can guess both of Alice's bits\ given that he learns one of the bits with certainty. Here we propose a protocol and show that as long as Alice is restricted to individual measurements, then both $P_{Alice}^{\ast }$ and $P_{Bob}^{\ast }$ can be made arbitrarily close to 1/2, so that maximal violation of the security bound can be reached. Even with some limited collective attacks, the security bound can still be violated. Therefore, although our protocol still cannot break the bound in principle when Alice has unlimited cheating power, it is sufficient for achieving secure quantum weak oblivious transfer in practice.

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arXiv2015

Security bound of cheat sensitive quantum bit commitment

Cheat sensitive quantum bit commitment (CSQBC) loosens the security requirement of quantum bit commitment (QBC), so that the existing impossibility proofs of unconditionally secure QBC can be evaded. But here we analyze the common features in all existing CSQBC protocols, and show that in any CSQBC having these features, the receiver can always learn a non-trivial amount of information on the sender's committed bit before it is unveiled, while his cheating can pass the security check with a probability not less than 50%. The sender's cheating is also studied. The optimal CSQBC protocols that can minimize the sum of the cheating probabilities of both parties are found to be trivial, as they are practically useless. We also discuss the possibility of building a fair protocol in which both parties can cheat with equal probabilities.

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arXiv2015

Can relativistic bit commitment lead to secure quantum oblivious transfer?

While unconditionally secure bit commitment (BC) is considered impossible within the quantum framework, it can be obtained under relativistic or experimental constraints. Here we study whether such BC can lead to secure quantum oblivious transfer (QOT). The answer is not completely negative. On one hand, we provide a detailed cheating strategy, showing that the "honest-but-curious adversaries" in some of the existing no-go proofs on QOT still apply even if secure BC is used, enabling the receiver to increase the average reliability of the decoded value of the transferred bit. On the other hand, it is also found that some other no-go proofs claiming that a dishonest receiver can always decode all transferred bits simultaneously with reliability 100% become invalid in this scenario, because their models of cryptographic protocols are too ideal to cover such a BC-based QOT.

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arXiv2014

Simplified quantum bit commitment using single photon nonlocality

We simplified our previously proposed quantum bit commitment (QBC) protocol based on the Mach-Zehnder interferometer, by replacing symmetric beam splitters with asymmetric ones. It eliminates the need for random sending time of the photons; thus, the feasibility and efficiency are both improved. The protocol is immune to the cheating strategy in the Mayers-Lo-Chau no-go theorem of unconditionally secure QBC, because the density matrices of the committed states do not satisfy a crucial condition on which the no-go theorem holds.

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arXiv2013

Security limitation on a class of device-independent quantum key distribution

Recently there were many proposals on device-independent (DI) quantum key distribution protocol whose security is based on the violation of the Clauser-Horne-Shimony-Holt inequality. However, as a statistical law, a certain extent of fluctuation has to be allowed. We show that the eavesdropper can make use of this property to obtain a remarkable part of the secret key by replacing some of the DI nonlocal boxes with local ones. On the contrary, the same cheating strategy does not apply to the device-dependent (DD) version of the protocol. Thus such kind of DI protocol is less secure than its DD counterpart.

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arXiv2013

Secure quantum bit commitment against empty promises. II. The density matrix

We further study the security of the quantum bit commitment (QBC) protocol we previously proposed [Phys. Rev. A 74, 022332 (2006).], by analyzing the reduced density matrix ρ_{b}^{B} which describes the quantum state at Bob's side corresponding to Alice's committed bit b. It is shown that Alice will find ρ_{0}^{B}\perp ρ_{1}^{B} while the protocol remains concealing to Bob. On the contrary, the existing no-go theorem of unconditionally secure QBC is based on the condition ρ_{0}^{B}\simeq ρ_{1}^{B}. Thus the specific cheating strategy proposed in the no-go theorem does not necessarily applies to our protocol.

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arXiv2013

Comment on "A short impossibility proof of quantum bit commitment"

In a recent letter (Phys. Lett. A 377 (2013) 1076, arXiv:0905.3801), the authors presented an impossibility proof of quantum bit commitment, which attempted to cover all possible protocols that involve both quantum and classical information. Here we show that there are many errors in the proof, thus it fails to exhaust all conceivable protocols.

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arXiv2013

Quantum protocols for the millionaire problem with a third party are trivial

Recently there were many quantum protocols devoted to solve the millionaire problem and private comparison problem by adding a semi-honest third party. They all require complicated quantum methods, while still leak a non-trivial amount of information to at least one of the parties. But it will be shown here that once the third party is introduced, there are very simple protocols which require quantum key distribution as the only quantum resource, and the amount of information leaked can be made arbitrarily small. Furthermore, even a dishonest third party cannot spoil the protocols. Thus our solutions surpass all existing protocols on both feasibility and security.

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arXiv2012

Comment on "Complete insecurity of quantum protocols for classical two-party computation"

In a recent paper (Phys. Rev. Lett. 109, 160501 (2012). arXiv:1201.0849), it is claimed that any quantum protocol for classical two-sided computation between Alice and Bob can be proven completely insecure for Alice if it is secure against Bob. Here we show that the proof is not sufficiently general, because the security definition it based on is only a sufficient condition but not a necessary condition.

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arXiv2012

Quantum key distribution based on orthogonal states allows secure quantum bit commitment

For more than a decade, it was believed that unconditionally secure quantum bit commitment (QBC) is impossible. But basing on a previously proposed quantum key distribution scheme using orthogonal states, here we build a QBC protocol in which the density matrices of the quantum states encoding the commitment do not satisfy a crucial condition on which the no-go proofs of QBC are based. Thus the no-go proofs could be evaded. Our protocol is fault-tolerant and very feasible with currently available technology. It reopens the venue for other "post-cold-war" multi-party cryptographic protocols, e.g., quantum bit string commitment and quantum strong coin tossing with an arbitrarily small bias. This result also has a strong influence on the Clifton-Bub-Halvorson theorem which suggests that quantum theory could be characterized in terms of information-theoretic constraints.

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arXiv2011

Single qubit quantum secret sharing with improved security

Analyzing carefully an experimentally feasible non-entangled single qubit quantum secret sharing protocol and its modified version [Phys. Rev. Lett. 95, 230505 (2005); ibid. 98, 028902 (2007)], it is found that both versions are insecure against coherent attacks though the original idea is so remarkable. To overcome this fatal flaw, here we propose a protocol with a distinct security checking strategy, which still involves single qubit operations only, making it possible to achieve better security of quantum secret sharing with current technology.

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arXiv2009

An experimentally testable proof of the discreteness of time

By proposing a paradox between the impossibility of superluminal signal transfer and the normalization condition of wavefunctions, we predict that when a change happens to the conditions that determining the status of a quantum system, the system will show no response to this change at all, until after a certain time interval. Otherwise either special relativity or quantum mechanics will be violated. As a consequence, no physical process can actually happen within Planck time. Therefore time is discrete, with Planck time being the smallest unit. More intriguingly, systems with a larger size and a slower speed will have a larger unit of time. Unlike many other interpretations of the discreteness of time, our proof can be tested, at less partly, by experiments. Our result also sets a limit on the speed of computers, and gives instruction to the search of quantum gravity theories.

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arXiv2009

Feasible scheme for measuring experimentally the speed of the response of quantum states to the change of the boundary condition

When the boundary condition of a quantum system changes, how fast will it affect the state of the system? Here we show that if the response takes place immediately, then it can allow superluminal signal transfer. Else if the response propagates in space with a finite speed, then it could give a simple explanation why our world shows classicality on the macroscopic scale. Furthermore, determining the exact value of this speed can either clarify the doubts on static experiments for testing Bell's inequality, or support the pilot-wave interpretation of quantum mechanics. We propose an experimental scheme for measuring this speed, which can be implemented with state-of-art technology, e.g., single-electron biprism interference.

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arXiv2009

Relationship between quantum repeating devices and quantum seals

It is revealed that quantum repeating devices and quantum seals have a very close relationship, thus the theory in one field can be applied to the other. Consequently, it is shown that the fidelity bounds and optimality of quantum repeating devices can be violated when they are used for decoding classical information from quantum states, and security bounds for protocols sealing quantum data exist.

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arXiv2008

Quantum secret sharing based on Smolin states alone

It was indicated [Yu 2007 Phys. Rev. A 75 066301] that a previous proposed quantum secret sharing (QSS) protocol based on Smolin states [Augusiak 2006 Phys. Rev. A 73 012318] is insecure against an internal cheater. Here we build a different QSS protocol with Smolin states alone, and prove it to be secure against known cheating strategies. Thus we open a promising venue for building secure QSS using merely Smolin states, which is a typical kind of bound entangled states. We also propose a feasible scheme to implement the protocol experimentally.

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arXiv2008

Practically secure quantum bit commitment based on quantum seals

The relationship between the quantum bit commitment (QBC) and quantum seal (QS) is studied. It is elaborated that QBC and QS are not equivalent, but QS protocols satisfying a stronger unconditional security requirement can lead to an unconditionally secure QBC. In this sense, QS is strictly stronger than QBC in security requirements. Based on an earlier proposal on sealing a single bit, a feasible QBC protocol is also put forward, which is secure in practice even if the cheater has a strong quantum computational power.

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arXiv2006

Comment on "Quantum string seal is insecure"

Recently an attack strategy was proposed by Chau [H. F. Chau, quant-ph/0602099 v3], which was claimed to be able to break all quantum string seal protocols, including the one proposed by He [G. P. He, Int. J. Quant. Inform. 4, 677 (2006)]. Here it will be shown that the information obtained in He's protocol by the attack is trivial. Thus Chau's conclusion that all quantum string seals are insecure is wrong. It will also be shown that some other claims in Chau's paper are inaccurate either.

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