No Signaling and Quantum Key Distribution

Barrett, Jonathan; Hardy, Lucién; Kent, Adrian

doi:10.1103/physrevlett.95.010503

Cited by 858 publications

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“…It guarantees that, for instance, pairs of photons can be treated as individual objects with individual properties and without any hidden correlations to other pairs. These, and many other results, addressed a number of subtleties and, finally, twenty years after its inception, the original entanglement-based key distribution protocol 7 has been shown to offer security even if the devices are not fully trusted and are exposed to noise 15,16,17,18,19,20 . This is assuming that quantum theory is all that there is, and that Eve is bound by the laws of quantum physics.…”

Section: Practicalitiesmentioning

confidence: 97%

“…Barring this, once the devices pass a certain statistical test they can be purchased without any knowledge of their internal working. This is a truly remarkable feat, also referred to as 'deviceindependent' cryptography 14,15,16,17,18,19,20 . Needless to say, proving security under such weak assumptions, with all the mathematical subtleties, is considerably more challenging than in the case of trusted devices, but the rapid progress in the past few years has been very encouraging, making device-independent cryptography one of the most active areas of quantum information science.…”

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confidence: 99%

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The ultimate physical limits of privacy

Ekert

Renner

2014

Nature

122

104

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Among those who make a living from the science of secrecy, worry and paranoia are just signs of professionalism. Can we protect our secrets against those who wield superior technological powers? Can we trust those who provide us with tools for protection? Can we even trust ourselves, our own freedom of choice? Recent developments in quantum cryptography show that some of these questions can be addressed and discussed in precise and operational terms, suggesting that privacy is indeed possible under surprisingly weak assumptions.Edgar Allan Poe, an American writer and an amateur cryptographer, once wrote "… it may be roundly asserted that human ingenuity cannot concoct a cipher which human ingenuity cannot resolve …" 1 . Is it true? Are we doomed to be deprived of our privacy, no matter how hard we try to retain it? If the history of secret communication is of any guidance here, the answer is a resounding 'yes'. There is hardly a shortage of examples illustrating how the most brilliant efforts of code-makers were matched by the ingenuity of code-breakers 2 . Even today, the best that modern cryptography can offer are security reductions, telling us, for example, that breaking RSA, one of the most widely used public key cryptographic systems, is at least as hard as factoring large integers 3 . But is factoring really hard? Not with quantum technology. Indeed, RSA, and many other public key cryptosystems, will become insecure once a quantum computer is built 4 . Admittedly, that day is probably decades away, but can anyone prove, or give any reliable assurance, that it is? Confidence in the slowness of technological progress is all that the security of our best ciphers now rests on.This said, the requirements for perfectly secure communication are well understood. When technical buzzwords are stripped away, all we need to construct a perfect cipher is shared private randomness, more precisely, a sequence of random bits known as a 'cryptographic key'. Any two parties who share the key, we call them Alice and Bob (not their real names, of course), can then use it to communicate secretly, using a simple encryption method known as the one-time pad 5 . The key is turned into a meaningful message by one party telling the other, in public, which bits of the key should be flipped. An eavesdropper, Eve, who has monitored the public communication and knows the general method of encryption but not the key will not be able to infer anything useful about the message. It is vital though that the key bits be truly random, never reused, and securely delivered to Alice and Bob, who may be miles apart. This is not easy, but it can be done, and one can only be amazed how well quantum physics lends itself to the task of key distribution.Quantum key distribution, proposed independently by Bennett and Brassard 6 and by Ekert 7 , derives its security either from the Heisenberg uncertainty principle (certain pairs of physical properties are complementary in the sense that knowing one property necessarily precludes knowledge about the othe...

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Section: Practicalitiesmentioning

confidence: 97%

mentioning

confidence: 99%

The ultimate physical limits of privacy

Ekert

Renner

2014

Nature

122

104

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“…BHK showed [4] how nonlocal correlations can be used as the basis of a key distribution scheme that is secure against nonsignaling eavesdroppers. Nonlocal correlations can also be used to give at least partial security against nonsignaling eavesdroppers in more practical quantum key distribution schemes [17,18].…”

Section: Is a Prl 97 170409 (2006) P H Y S I C A L R E V I E W L E Tmentioning

confidence: 99%

“…For example, the nonlocality of quantum correlations allows communication complexity problems to be solved using an amount of communication that is smaller than is possible classically [3]. Barrett-Hardy-Kent (BHK) recently showed that testing particular nonlocal quantum correlations allows two parties to distribute a secret key securely, in such a way that the security is guaranteed by the no-signaling principle alone [4] (i.e., without relying on the validity of quantum theory).…”

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confidence: 99%

Maximally Nonlocal and Monogamous Quantum Correlations

2006

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We introduce a version of the chained Bell inequality for an arbitrary number of measurement outcomes and use it to give a simple proof that the maximally entangled state of two d-dimensional quantum systems has no local component. That is, if we write its quantum correlations as a mixture of local correlations and general (not necessarily quantum) correlations, the coefficient of the local correlations must be zero. This suggests an experimental program to obtain as good an upper bound as possible on the fraction of local states and provides a lower bound on the amount of classical communication needed to simulate a maximally entangled state in d d dimensions. We also prove that the quantum correlations violating the inequality are monogamous among nonsignaling correlations and, hence, can be used for quantum key distribution secure against postquantum (but nonsignaling) eavesdroppers. Quantum theory predicts that measurements on separated entangled systems will produce outcome correlations that, in Bell's terminology [1], are not locally causal or, in what has become standard terminology, are nonlocal. In particular, if a Bell inequality is violated, then one cannot consistently assume that the outcomes of measurements on each system are predetermined and independent of the measurements carried out on the other system(s). Violation of Bell inequalities has been confirmed in numerous experiments [2].Violation of Bell inequalities not only tells us something fundamental about nature but also has practical applications. For example, the nonlocality of quantum correlations allows communication complexity problems to be solved using an amount of communication that is smaller than is possible classically [3]. Barrett-Hardy-Kent (BHK) recently showed that testing particular nonlocal quantum correlations allows two parties to distribute a secret key securely, in such a way that the security is guaranteed by the no-signaling principle alone [4] (i.e., without relying on the validity of quantum theory).In this Letter, we extend the chained Bell inequality to an inequality with an arbitrary number of measurement outcomes, which can thus be applied to states in arbitrary dimensions. In the limit of a large number of measurement settings, quantum mechanics predicts correlations for a maximally entangled bipartite state that resemble those of the tripartite Greenberger-Horne-Zeilinger (GHZ) state in that, with probability tending to one, the predictions of any local hidden variable model contradict those of quantum mechanics for at least one pair of measurements. We use this to give a constructive proof of a result originally due to Elitzur, Popescu, and Rohrlich (EPR) [5]: If the quantum correlations of a maximally entangled state of two qubits are written as a convex combination of local and nonlocal correlations, then the local fraction must be zero. Our proof extends EPR's result to maximally entangled states in any dimension and also removes the need for a technical assumption required for EPR's original proof [6]. Mor...

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“…Quantum mechanics has been tested experimentally for nearly a century, to very high precision. But even if quantum mechanics is superseded by a new physical theory, it is not necessarily true that quantum key distribution would be insecure: for example, secure key distribution can be achieved in a manner similar to QKD solely based on the assumption that no faster-than-light communication is possible [BHK05].…”

Section: The Security Of Qkdmentioning

confidence: 99%

The Case for Quantum Key Distribution

Stebila

Mosca

Lütkenhaus

2010

Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering

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Quantum key distribution (QKD) promises secure key agreement by using quantum mechanical systems. We argue that QKD will be an important part of future cryptographic infrastructures. It can provide long-term confidentiality for encrypted information without reliance on computational assumptions. Although QKD still requires authentication to prevent man-in-the-middle attacks, it can make use of either information-theoretically secure symmetric key authentication or computationally secure public key authentication: even when using public key authentication, we argue that QKD still offers stronger security than classical key agreement.

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No Signaling and Quantum Key Distribution

Cited by 858 publications

References 15 publications

The ultimate physical limits of privacy

The ultimate physical limits of privacy

Maximally Nonlocal and Monogamous Quantum Correlations

The Case for Quantum Key Distribution

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