Abstract
Secret sharing is a multiparty cryptographic primitive that can be applied to a network of partially distrustful parties for encrypting data that is both sensitive (it must remain secure) and important (it must not be lost or destroyed). When sharing classical secrets (as opposed to quantum states), one can distinguish between protocols that leverage bipartite quantum key distribution (QKD) and those that exploit multipartite entanglement. The latter class are known to be vulnerable to so-called participant attacks and, while progress has been made recently, there is currently no analysis that quantifies their performance in the composable, finite-size regime, which has become the gold standard for QKD security. Given this—and the fact that distributing multipartite entanglement is typically challenging—one might well ask is there any virtue in pursuing multipartite entanglement-based schemes? Here, we answer this question in the affirmative for a class of secret-sharing protocols based on continuous-variable graph states. We establish security in a composable framework and identify a network topology, specifically a bottleneck network of lossy channels, and parameter regimes within the reach of present-day experiments for which a multipartite scheme outperforms the corresponding QKD-based method in the asymptotic and finite-size setting. Finally, we establish experimental parameters where the multipartite schemes outperform any possible QKD-based protocol. This is one of the first concrete compelling examples of multipartite entangled resources achieving a genuine advantage over point-to-point protocols for quantum communication and represents a rigorous, operational benchmark to assess the usefulness of such resources.
- Received 10 May 2021
- Accepted 25 October 2021
DOI:https://doi.org/10.1103/PRXQuantum.2.040339
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
This work presents a cryptographic application of multipartite entanglement that serves as a rigorous and practical benchmark for near-term quantum networks. Numerous applications exist for a future “quantum internet” of connected, fault-tolerant devices, but there are remarkably few concrete proposals for small-scale, near-term implementations. We address this by solving the longstanding open problem of sharing classical secrets via multipartite entanglement in a way that is composably secure and resistant to participant attacks. Applying our results to a bottleneck network of fiber-optic channels we find that for metropolitan distances, a tripartite entangled protocol using present-day technology can outperform an equivalent bipartite scheme.
