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Device-independent cryptography using intra-particle entanglement

Satyabrata Adhikari, Dipankar Home, A. S. Majumdar, A. K. Pan, R. Srikanth, Soumyakanti Bose

Published Sep 3, 2013• 1 citation
OpenAlex

Abstract

Poornaprajna Institute of Scienti c Research, Bangalore, India(Dated:)It is known that entanglement helps enhance security of practical quantum key distribution againstcertain classes of attacks that exploit aws in the devices. However, bipartite or multipartite en-tanglement itself is a costly resource. We point out how intra-particle entanglement, which is easilygenerated using linear optics, can be useful here, comparing and contrasting its usage with con-ventional, inter-particle entanglement. In particular, by virtue of its local nature, the amount ofBell-inequality violation in intraparticle entanglement must be measured locally. This, in turn, helpsdecouple device errors from channel errors in a natural way. The amount of Bell-inequality violationobserved by Alice determines the error that can be tolerated in the channel. We illustrate theseideas by means of a simple incoherent attack on the channel, augmented by a side channel attackon the devices used.

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Poornaprajna Institute of Scienti c Research, Bangalore, India(Dated:)It is known that entanglement helps enhance security of practical quantum key distribution againstcertain classes of attacks that exploit aws in the devices. However, bipartite or multipartite en-tanglement itself is a costly resource. We point out how intra-particle entanglement, which is easilygenerated using linear optics, can be useful here, comparing and contrasting its usage with con-ventional, inter-particle entanglement. In particular, by virtue of its local nature, the amount ofBell-inequality violation in intraparticle entanglement must be measured locally. This, in turn, helpsdecouple device errors from channel errors in a natural way. The amount of Bell-inequality violationobserved by Alice determines the error that can be tolerated in the channel. We illustrate theseideas by means of a simple incoherent attack on the channel, augmented by a side channel attackon the devices used.
We explore the use of the resource of intra-particle entanglement for secure quantum key distribution in the device-independent scenario. By virtue of the local nature of such entanglement, Bell tests must be implemented locally, which leads to a natural decoupling of device errors from channel errors. We consider a side channel attack on the sender's state preparation device, for which the intra-particle-entanglement based scheme is shown to be more secure than the one that uses separable states. Of practical relevance is the fact that such entanglement can be easily generated using linear optics.
The concept of the Device-Independent Quantum Key Distribution (DI-QKD) constitutes the minimalist paradigm for quantum cryptography, in which the security of the distributed secret key is fully assured by the statistical properties of the data being shared between the parties that perform a quantum-based protocol. In particular, the secrecy of the distributed key is ultimately guaranteed not only thanks to the quantum nature of the underlying scheme, but also without making any assumptions about the operation of the devices being employed. Such a conservative approach is possible thanks to the non-local correlations exhibited within the shared data, i.e., the correlations of genuine quantum origin that, due to violation of a particular Bell inequality, cannot be explained by any form of common randomness pre-available to the parties. Such violation, however, must be revealed without performing any post-selection on the data, what would then open the so-called detection loophole and jeopardize the security of the protocol. In spite of the tremendous advances recently made to achieve higher detection efficiencies in Bell-violation experiments, DI-QKD remains a very experimentally difficult task due to the exponential increase of loss in the channel, e.g., implemented with optical fibres, with the distance separating the parties involved. Here, we describe a new and plausible solution to overcome the crucial problem of channel loss in the frame of DI-QKD optical implementations. In particular, we propose a novel protocol inspired by the entanglement swapping schemes, which by the usage of the state-of-the-art (e.g., quantum-dot-based or heralded) single-photon sources has potential, for the first time, to be implementable with current photonic and linear optics technologies. While allowing for any transmission losses that only decrease the rate of the key distribution without creating vulnerability, it tolerates overall detection efficiency at the 90% level even when requiring strict device-independence. We compare our scheme against protocols that involve sources based on spontaneous parametric down-conversion (SPDC), in order to explicitly show and explain why such SPDC-based proposals—even when enhanced by the entanglement swapping or qubit amplification techniques—are then largely outperformed when physical imperfections are rigorously taken into account.
Device-independent quantum key distribution (DIQKD) in its current design requires a violation of a Bell's inequality between two parties, Alice and Bob, who are connected by a quantum channel. However, in reality, quantum channels are lossy and current DIQKD protocols are thus vulnerable to attacks exploiting the detection loophole of the Bell test. Here, we propose a novel approach to DIQKD that overcomes this limitation. In particular, we propose a protocol where the Bell test is performed entirely on two casually independent devices situated in Alice's laboratory. As a result, the detection loophole caused by the losses in the channel is avoided.
Quantum key distribution (QKD) with security features based on the notion of nonlocality has provided valuable insights into the possibility of device-independent scenarios. The essential resource for nonlocality in Nature described by quantum physics has been mainly associated with entanglement of two particles or more, although it has been shown that nonlocality of a single particle is indeed possible. Here, we consider a quantum key distribution scheme based on Phys. Rev. A, 68 (2003) 012324 exploiting single-particle nonlocality testing to demonstrate its security. We present our analysis of security against individual attack within a device-independent scenario where Eve is constrained only by the no-signaling principle. We further consider a family of QKD protocols based on binary measurements and discuss the possibility of optimal scenarios.
Entanglement is one of the most striking phenomena in quantum physics, playing important roles in fundamental physics and quantum information science. It enables a secure means of communication—quantum cryptography—and builds up the foundation of its unconditional security. Entanglement-based quantum cryptography has received great attention from the early demonstrations to the recent remarkable achievements. In a practical scenario, although entanglement-based quantum cryptography can provide inherent source-independent security, its detection side has been shown to be vulnerable to external probing attacks. Here we show that entanglement swapping can effectively solve this critical issue, enabling a side-channel-free quantum cryptography.Entanglement swapping allows each user’s quantum state preparation and detection in a completely private station, which is immune to any external probing side channels. We demonstrate the entanglement-swapping quantum cryptography scheme in the field based on two independent entanglement photon sources. Based on the remote entangled photon pairs, we implement the Ekert-1991 protocol under a channel attenuation equivalent to 100 km of standard optical fiber, achieving a Bell violation value of S=2.659±0.092 and a secret key rate of 0.0163 bit/s. While recent device-independent QKD demonstrations have reached 100 km using atoms or ions, our photonic ES-QKD offers a complementary, all-optical pathway that is directly compatible with existing fiber networks and quantum repeaters.
Device-Independent Quantum Key Distribution (DI-QKD) represents the pinnacle of secure quantum communication, offering cryptographic guarantees that are independent of the trustworthiness of the devices used. Unlike traditional QKD schemes that rely on specific assumptions about internal device behaviour, DI-QKD leverages the violation of Bell inequalities to certify security solely from observed statistics. This approach eliminates a wide range of side-channel and implementation attacks, making it especially attractive for critical infrastructures and defense applications. The core concept hinges on the ability of the communicating parties, traditionally named Alice and Bob, to generate shared secret keys through the violation of Bell inequalities verified at a central node, named Charlie, regardless of hardware imperfections. Previous works demonstrated the feasibility of a Bell-certified key exchange over a real optical channel using a heralded entanglement scheme. This work aims to build on that foundation, presenting a full-stack engineering implementation of a DI-QKD system that includes industrial-grade entangled photon sources, high-efficiency SNSPD detectors, central-node heralding logic, and a real-time software stack for key management, observability, and integration with classical IT infrastructure.