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arXiv:2610.32923

One-sided-DIQKD using any pure bipartite entangled state secure against all attacks

Bohnishikha Ghosh, Chithra Raj, Shubhayan Sarkar

quant-phSubmitted Oct 23, 2026• Announced Oct 26, 2026• 0 citations
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Abstract

Quantum Key Distribution (QKD) allows spatially separated parties to establish a secret key among themselves based on quantum principles. While QKD systems are being deployed worldwide, their reliance on trusted measurements makes them vulnerable. Moreover, existing protocols have largely focussed on the qubit cases, and rely on the maximally entangled state, a costly resource to generate. Here, we consider the one-sided-device-independent (1SDI) QKD protocols, where one of the measurement devices is trusted while the other is untrusted. The resource in this scenario is quantum steering, an asymmetric form of quantum nonlocality. This is inspired by a real-world scenario, where the trusted party can be considered to be a bank, or any large organisation that has sufficient resources to protect its systems and validate them, while the users are vulnerable to attacks. We then demonstrate that a secure key can be obtained using any pure bipartite entangled state in this setup. Considering realistic detectors and sources based on current technology, we demonstrate that even states that are almost separable can be used to extract a secure key. Moreover, for every pure entangled bipartite state, we find the critical detection efficiencies and visibility to obtain a secure key.

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6+3 pages, comments are welcome:)

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Quantum Key Distribution (QKD) allows spatially separated parties to establish a secret key among themselves based on quantum principles. While QKD systems are being deployed worldwide, their reliance on trusted measurements makes them vulnerable. Moreover, existing protocols have largely focussed on the qubit cases, and rely on the maximally entangled state, a costly resource to generate. Here, we consider the one-sided-device-independent (1SDI) QKD protocols, where one of the measurement devices is trusted while the other is untrusted. The resource in this scenario is quantum steering, an asymmetric form of quantum nonlocality. This is inspired by a real-world scenario, where the trusted party can be considered to be a bank, or any large organisation that has sufficient resources to protect its systems and validate them, while the users are vulnerable to attacks. We then demonstrate that a secure key can be obtained using any pure bipartite entangled state in this setup. Considering realistic detectors and sources based on current technology, we demonstrate that even states that are almost separable can be used to extract a secure key. Moreover, for every pure entangled bipartite state, we find the critical detection efficiencies and visibility to obtain a secure key.
Transmitter-side device dependence is a longstanding yet implicit problem in quantum key distribution (QKD), in contrast to the thoroughly addressed measurement-side case. Quantum steering, which intrinsically distinguishes the roles of sender and receiver in entanglement certification, offers a natural route to lifting trust assumptions on the transmitter. Existing one-sided device-independent (1sDI) protocols that exploit quantum steering as the security resource typically operate in a tripartite architecture, whereas adapting them to a transmitter-receiver architecture can introduce a signaling loophole. Here we conceptually formalize the transmitter-device-independence on the basis of faithful quantum steering and propose a practical transmitter-device-independent (TDI) QKD protocol within the 1sDI trust model. The TDI scheme operationalizes the implicit no-signaling condition by enforcing a causal isolation between the input information and the transmitted quantum states, thereby eliminating the associated transmitter-side device vulnerabilities. In a proof-of-principle experiment, we validate the feasibility of the TDI protocol, achieving a key rate in the asymptotic limit of 410~bps over 27~km spool fiber. By delivering TDI security while retaining strong loss tolerance, our approach helps bridge the gap between security and practicality for real-world QKD deployments.
Abstract Quantum key distribution (QKD) is a technique enabling provable secure communication but faces challenges in device characterisation, posing potential security risks. Device-independent (DI) QKD protocols overcome this issue by making minimal device assumptions but are limited in distance because they require high detection efficiencies, which refer to the ability of the experimental setup to detect quantum states. It is thus desirable to find QKD protocols that are based on realistic assumptions on the devices as well as implementable over long distances. In this work, we consider a one-sided DI QKD scheme with two measurements per party and show that it is secure against coherent attacks up to detection efficiencies greater than 50.1% specifically on the untrusted side. This is almost the theoretical limit achievable for protocols with two untrusted measurements. Interestingly, we also show that, by placing the source of states close to the untrusted side, our protocol is secure over distances comparable to standard QKD protocols.
Quantum key distribution (QKD) brings the promise of communication with information-theoretic security but is limited in practice due to its susceptibility to noise, losses, and device imperfections. To address these challenges, we propose a robust high-dimensional (HD) one-sided device-independent QKD (1sDI-QKD) protocol and present a proof-of-principle experimental implementation using photons entangled in the transverse-spatial degree-of-freedom. We develop a systematic security analysis of HD 1sDI-QKD protocols, leveraging quantum steering to certify security, and evaluate achievable secret key rates for different measurement configurations and system dimensions using reverse reconciliation. Our analysis shows that increasing the dimension enhances robustness against both noise and loss. We then demonstrate the key experimental building blocks required for implementing the protocol: (a) a high-quality source of high-dimensional photonic entanglement, and (b) a fully programmable, high-dimensional multi-outcome measurement device operating in up to dimension 11. Using these components, we obtain positive key rates for all investigated dimensions under the fair-sampling assumption, with the highest key rates achieved for dimension d=7. Finally, we discuss the steps required for a practical, loophole-free implementation of 1sDI-QKD in realistic regimes of loss and noise.
ABSTRACT Quantum key distribution (QKD) is based on the laws of quantum mechanics to enable provably secure communication. Despite its theoretical security promise, practical QKD systems are vulnerable to serious attacks, including side‐channel attacks and detector loopholes, and assumes a trusted device characterisation. Device‐independent quantum key distribution (DIQKD) overcomes these limitations by relying solely on observed nonlocal correlations, certified through Bell inequality violations, thereby removing assumptions about the internal workings of the measurement devices. In this paper, we first review the foundational principles underlying DIQKD, including Bell tests and security definitions. We then examine a range of protocol designs, including CHSH‐based schemes, and non‐local game frameworks, alongside with their security proofs. We also assess recent experimental implementations and discuss source architectures, detection technologies and finite‐key analyses. Finally, we identify current open problems, such as noise tolerance, generation rates and integration with quantum networks and outline promising directions for future research to realize robust high‐performance DIQKD.
Device-independent quantum key distribution (DIQKD) aims at generating secret keys between distant parties without the parties trusting their devices. We investigate a proposal for performing fully photonic DIQKD, based on single photon sources and heralding measurements at a central station placed between the two parties. We derive conditions to attain non-zero secret-key rates in terms of the photon efficiency, indistinguishability and the second order autocorrelation function of the single-photon sources. Exploiting new results on the security bound of such protocols allows us to reduce the requirements on the physical parameters of the setup. Our analysis shows that in the considered schemes, key rates of several hundreds of secret bits per second are within reach at distances of several tens of kilometers.
One-sided device-independent quantum key distribution (1SDI-QKD) offers a practical middle ground between fully device-independent protocols and standard QKD, achieving security with detection efficiencies as low as 50.1\% on the untrusted side. However, prior analyses assumed idealized channels. This work extends the 1SDI-QKD framework to amplitude damping, dephasing, and depolarizing noise. Results reveal a clear noise hierarchy: dephasing tolerates the most noise before security is lost (pcrit≈0.50p_{\text{crit}} \approx 0.50pcrit​≈0.50 versus 0.449 and 0.220 respectively), while depolarizing noise imposes the most stringent detection efficiency requirements, exceeding 97\% at 20\% noise where amplitude damping requires 76\%. Security is lost while substantial entanglement remains (C≈0.67C \approx 0.67C≈0.67--0.740.740.74), demonstrating that steering violation, not merely entanglement, determines 1SDI-QKD security. Integrating the BBPSSW purification protocol shows that it functions primarily as a range-extension mechanism: five rounds extend dephasing-limited operation from 10~km to 36~km at 90\% detection efficiency. Accounting for both the 2n2^n2n pair cost and the cumulative success probability, the effective rate peaks at $ 10^{-3}$ bits per initial pair for dephasing but only $ 10^{-6}$ for amplitude damping and depolarizing noise, identifying phase noise limited links as the regime where purification is worthwhile.