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Experimental Quantum Cryptography With Classical Users

Francesco Massa, Preeti Yadav, Amir Moqanaki, Walter O. Krawec, Paulo Mateus, Nikola Paunković, André Souto, Philip John Walther

Published Aug 5, 2019• 8 citations
OpenAlex

Abstract

The exploit of quantum systems allows for insights that promise to revolutionise information processing, although a main challenge for practical implementations is technological complexity. Due to its feasibility, quantum cryptography, which allows for perfectly secure communication, has become the most prominent application of quantum technology. Nevertheless, this task still requires the users to be capable of performing quantum operations, such as state preparation or measurements in multiple bases. A natural question is whether the users' technological requirements can be further reduced. Here we demonstrate a novel quantum cryptography scheme, where users are fully classical. In our protocol, the quantum operations are performed by an untrusted third party acting as a server, which gives the users access to a superimposed single photon, and the key exchange is achieved via interaction-free measurements on the shared state. Our approach opens up new interesting possibilities for quantum cryptography networks.

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•Jan 1, 2017•1 citation
The exploit of quantum systems allows for insights that promise to revolutionise information processing, although a main challenge for practical implementations is technological complexity. Due to its feasibility, quantum cryptography, which allows for perfectly secure communication, has become the most prominent application of quantum technology. Nevertheless, this task still requires the users to be capable of performing quantum operations, such as state preparation or measurements in multiple bases. A natural question is whether the users' technological requirements can be further reduced. Here we demonstrate a novel quantum cryptography scheme, where users are fully classical. In our protocol, the quantum operations are performed by an untrusted third party acting as a server, which gives the users access to a superimposed single photon, and the key exchange is achieved via interaction-free measurements on the shared state. Our approach opens up new interesting possibilities for quantum cryptography networks.
Quantum key distribution, which allows two distant parties to share an unconditionally secure cryptographic key, promises to play an important role in the future of communication. For this reason such technique has attracted many theoretical and experimental efforts, thus becoming one of the most prominent quantum technologies of the last decades. The security of the key relies on quantum mechanics and therefore requires the users to be capable of performing quantum operations, such as state preparation or measurements in multiple bases. A natural question is whether and to what extent these requirements can be relaxed and the quantum capabilities of the users reduced. Here we demonstrate a novel quantum key distribution scheme, where users are fully classical. In our protocol, the quantum operations are performed by an untrusted third party acting as a server, which gives the users access to a superimposed single photon, and the key exchange is achieved via interaction-free measurements on the shared state. We also provide a full security proof of the protocol by computing the secret key rate in the realistic scenario of finite-resources, as well as practical experimental conditions of imperfect photon source and detectors. Our approach deepens the understanding of the fundamental principles underlying quantum key distribution and, at the same time, opens up new interesting possibilities for quantum cryptography networks
An efficient quantum cryptography network protocol is proposed with d -dimensional polarized photons, without resorting to entanglement and quantum memory. A server on the network, say Alice, provides the service for preparing and measuring single photons whose initial state are |0⟩. The users code the information on the single photons with some unitary operations. To prevent the untrustworthy server Alice from eavesdropping the quantum lines, a nonorthogonal-coding technique is used in the process that the quantum signal is transmitted between the users. This protocol does not require the servers and the users to store the quantum states and almost all of the single photons can be used for carrying the information, which makes it more convenient for application than others with present technology. We also discuss the case with a faint laser pulse.
Communications in secrecy are often required in many commercial and military applications. Unfortunately, many cryptographic schemes in use today such as public-key cryptography based on the RSA algorithm would be broken with either unanticipated advances in hardware and algorithm or the advent of quantum computers. Quantum cryptography, on the other hand, has been proven secure even against the most general attack allowed by the laws of physics and is a promising technology poised for widespread adoption in realistic cryptographic applications. Quantum cryptography allows two parties to expand on a secret key that they have previously shared. Various quantum cryptographic protocols have been proposed to perform this task. In this paper, we survey some popular quantum cryptographic protocols (including the famous Bennett-Brassard 1984 protocol) and discuss their security. Specifically, we consider their security in two cases: the ideal case where a perfect single-photon source is used and the practical case where a realistic laser source is used. We compare the protocols and find that the efficient six-state protocol outperforms the others both in the tolerable quantum bit error rate and in the key generation rate when a realistic laser source is used.
Counterfactual quantum cryptography allows two remote parties to share a secret key even though a physical particle is not in fact transmitted through the quantum channel. In order to extend the scope of counterfactual quantum cryptography, we use an untrusted relay to construct a multi-user network. The implementation issues are discussed to show that the scheme can be realized with current technologies. We also prove the practical security advantages of the scheme by eliminating the probability that an eavesdropper can directly access the signal or an untrusted relay can perform false operations.
Semiquantum key distribution allows a quantum party to share a random key with a "classical" party who only can prepare and measure qubits in the computational basis or reorder some qubits when he has access to a quantum channel. In this work, we present a protocol where a secret key can be established between a quantum user and an almost classical user who only needs the quantum ability to access quantum channels, by securely delegating quantum computation to a quantum server. We show the proposed protocol is robust even when the delegated quantum server is a powerful adversary, and is experimentally feasible with current technology. As one party of our protocol is the most quantum-resource efficient, it can be more practical and significantly widen the applicability scope of quantum key distribution.
Cryptographic world has faced multiple challenges that are included in encoding and decoding transmitting information into a secure communication channel. Quantum cryptography may be another generation of the cryptography world, which is based on the law of physics. After decades of using the classical cryptography, there is an essential need to move a step forward through the most trusted systems, especially enormous amount of data flows through billions of communicating channels (e.g. The internet), and keeping this transmitting information away from eavesdropping is obligatory. Moreover, quantum cryptography has proved its standing against many weaknesses in the classical cryptography. One of these weaknesses is the ability to copy any type of information using a passive attack without an interruption, which is impossible in the quantum system. Theoretically, several quantum observables are utilized to diagnose an action of one particle. These observables are included in measuring mass, movement, speed, etc. The polarization of one photon occurs normally and randomly in the space. Any interruption that happens during sending of a light will cause a deconstruction of the light polarization. Therefore, particles’ movement in a three-dimensional space is supported by Non-Cloning theory that makes eavesdroppers unable to interrupt a communication system. In case an eavesdropper tried to interrupt a photon, the photon will be destroyed after passing the photon into a quantum detector or any measurement device. In the last decades, many Quantum Key Distribution (QKD) protocols have been created to initiate a secret key during encoding and decoding transmitted data operations. Some of these protocols were proven un-secure based on the quantum attacks that were released early. Even though the power of physics is still active and the Non-Cloning theory is unbroken, some QKD protocols failed during the security measurements. The main reason of the failure is based on the inability to provide the authentication between the end users during the quantum and classical channels. The proposed QKD protocol was designed to utilize some advantages of quantum physics as well as solid functions that are used in the classical cryptography. The authentication is a requirement during different communication channels, where both legitimate parties must confirm their identities before starting to submit data (plain-text). Moreover, the protocol uses most needed scenarios to finish the communication without leaking important data. These scenarios have been approved in existing QKD protocols either by classical or quantum systems. The matrix techniques also are used as a part of the preparation of the authentication key, where the end users communicate by an EPR (related to Einstein, Podolsky, and Rosen theory in 1935) channel. The EPR channel will be supported by an entanglement of particles. If the EPR communication succeeded, transferring the converted plain-text is required. Finally, both end users will have an authenticated secret key, and the submission will be done without any interruption.