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Physical Review A

Experimental study of time-dependent side channels in quantum key distribution

Hao Tan, Weiyang Zhang, Liying Han, Sheng‐Kai Liao, Feihu Xu

Published Apr 28, 2025• 2 citations
Publisher

Abstract

Quantum key distribution allows remote parties to share secret keys with proven security. However, in most systems, these schemes will also modulate light that gets leaked between the signal pulses, resulting in time-dependent side channels. Here, the authors experimentally study practical quantum key distribution with these side channels, analyzing the security risks and the corresponding countermeasures.

DOI
10.1103/physreva.111.042622

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Quantum key distribution allows remote parties to share secret keys with proven security. However, in most systems, these schemes will also modulate light that gets leaked between the signal pulses, resulting in time-dependent side channels. Here, the authors experimentally study practical quantum key distribution with these side channels, analyzing the security risks and the corresponding countermeasures.
Quantum key distribution can provide unconditionally secure key exchange for remote users in theory. In practice, however, in most quantum key distribution systems, quantum hackers might steal the secure keys by observing the side channels in the emitted photons, such as the photon frequency spectrum, emission time, propagation direction, spatial angular momentum, and so on. It is hard to prevent such kinds of attacks because side channels may exist in many dimensions of the emitted photons. Here we report an experimental realization of a side-channel-secure quantum key distribution protocol which is not only measurement-device independent, but also immune to all side-channel attacks to the photons emitted from Alice's and Bob's labs. We achieve a secure key rate of 1.73×10^{-6} per pulse through 50 km fiber spools.
Abstract Security of quantum key distribution (QKD) is based on fundamental laws of quantum physics. However, the security of QKD implementations is at risk due to various deviations, called side channels, of the real device from the theoretical model. In this work, we discuss the practical ways to avoid the threat of side channels in QKD. We use interference visibility measurement for estimation of distinguishability of quantum signals, and show how to integrate it into the security proof. Our results paves the way towards the development of novel robust QKD schemes.
Quantum key distribution (QKD) theoretically provides unconditional security between remote parties. However, guaranteeing practical security through device characterization alone is challenging in real-world implementations due to the multidimensional spaces in which the devices may be operated. The side channel secure (SCS) QKD protocol, which only requires bounding the upper limits of the intensities for the two states, theoretically provides a rigorous solution to the challenge and achieves measurement-device-independent security in detection and security for whatever multidimensional side channel attack in the source. Here, we demonstrate a practical implementation of SCS-QKD, achieving a secure key rate of 6.67 kbps through a 50.5 km fiber and a maximum distribution distance of 101.1 km while accounting for finite-size effects. Our experiment also represents an approximately 40 times improvement over the previous experiment.
Cryptography plays a crucial and significant part in key transmission between two users. To send the keys in a secure manner, quantum implementations are used. A recent method of distributing keys across users is known as quantum key distribution. There is a substantial disconnect between quantum key distribution (QKD) theory and practice in this regard. Gadgets no longer meet the security evidence's assumptions. This hole is accessed as an input here. A simple and direct measurement methodology that is independent of the QKD device and is primarily based on any potential flaws and/or failures. A quantum language exchange facet channel that is part of the QKD device. Our simplest technique is experimentally give up to one unpaired parameter for each transmitted pulse. This explains the high dissatisfaction with the source. Also, unlike DI (Device Independent) QKD, Stats leaked from user labs critical to ensuring QKD's security avatar. In that sense, its security is more than what DI QKD offers, but it provides a secret.