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Quantum Technology: Driving Commercialisation of an Enabling Science

An investigation of jamming in free-space quantum key distribution

Cameron Simmons, Yoann Noblet, Alfonso Tello Castillo, Ross J. Donaldson

Published Jan 11, 2023• 3 citations
Publisher

Abstract

Quantum key distribution (QKD) is a quantum communications protocol which provides the growth of encryption keys under guaranteed security. Due to the single-photon nature of many QKD protocols, QKD systems can be optically jammed by overwhelming a receiver with many photons at wavelengths at which the single photon detectors are responsive, causing a prohibitively high quantum bit error rate (QBER). In satellite QKD (SatQKD), which relies on communication during brief satellite visual contact, short jamming periods could prevent access to secure communications for much longer periods of time. Optical jamming (OJ) can be achieved both from within line-of-sight by targeting the receiver with a light source, or, in the case of downlink SatQKD, from without line-of-sight by reflecting OJ light off the transmitting satellite.1 The latter attack can be effective 1000km from the ground station, which presents challenges to the deployment of SatQKD in mission-critical applications. In this work, we present two investigations for OJ attacks on SatQKD. Firstly, we present an experimental demonstration utilizing SPAD array technology to locate and mitigate within line-of-sight OJ at long range. Secondly, we present simulations quantifying the effectiveness of without line-of-sight OJ against SatQKD systems and outline mitigation techniques inspired by RF communications. Implementation of the mitigation techniques will be essential for defence applications.

DOI
10.1117/12.2644866

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Quantum key distribution (QKD) is a quantum communications protocol which provides the growth of encryption keys under guaranteed security. Due to the single-photon nature of many QKD protocols, QKD systems can be optically jammed by overwhelming a receiver with many photons at wavelengths at which the single photon detectors are responsive, causing a prohibitively high quantum bit error rate (QBER). In satellite QKD (SatQKD), which relies on communication during brief satellite visual contact, short jamming periods could prevent access to secure communications for much longer periods of time. Optical jamming (OJ) can be achieved both from within line-of-sight by targeting the receiver with a light source, or, in the case of downlink SatQKD, from without line-of-sight by reflecting OJ light off the transmitting satellite.1 The latter attack can be effective 1000km from the ground station, which presents challenges to the deployment of SatQKD in mission-critical applications. In this work, we present two investigations for OJ attacks on SatQKD. Firstly, we present an experimental demonstration utilizing SPAD array technology to locate and mitigate within line-of-sight OJ at long range. Secondly, we present simulations quantifying the effectiveness of without line-of-sight OJ against SatQKD systems and outline mitigation techniques inspired by RF communications. Implementation of the mitigation techniques will be essential for defence applications.
Entanglement-based quantum key distribution (QKD) protocols, such as E91 and BBM92, offer strong information-theoretic security and are naturally suited for satellite-to-satellite QKD (SatQKD) links. However, implementing these protocols over long-distance inter-satellite free-space optical (FSO) channels poses critical physical-layer challenges that are not addressed in the existing literature. In particular, photon losses due to beam divergence, pointing errors, and background noise can severely degrade the key generation rate and quantum bit error rate (QBER), especially under narrow receiver field-of-view (FoV) constraints. This paper presents a comprehensive performance analysis of entanglement-based inter-satellite QKD, focusing on photon-level modeling and the impact of practical impairments. We develop analytical expressions for signal detection probabilities, background photon influence, multi-pair emissions, and QBER, incorporating key parameters such as link distance, transmitter tracking jitter, receiver misalignment, and photon pair generation rate. Simulation results reveal the nonlinear sensitivity of system performance to tracking error and FoV limitations, and highlight optimal parameter regimes that jointly maximize secret key rate while maintaining QBER below acceptable thresholds. The proposed model provides actionable design insights for reliable and efficient deployment of entanglement-based SatQKD systems.
Satellite-mediated quantum key distribution (QKD) is set to become a critical technology for quantum-secure communication over long distances. While satellite QKD cannot be effectively eavesdropped, we show it can be disrupted (or 'jammed') with relatively simple and readily available equipment. We developed an atmospheric attenuation and satellite optical scattering model to estimate the rate of excess noise photons that can be injected into a satellite QKD channel by an off-axis laser, and calculated the effect this added noise has on the quantum bit error rate. We show that a ground-based laser on the order of 1 kW can significantly disrupt modern satellite QKD systems due to photons scattering off the satellite being detected by the QKD receiver on the ground. This class of laser can be purchased commercially, meaning such a method of disruption could be a serious threat to effectively securing high-value communications via satellite QKD in the future. We also discuss these results in relation to likely future developments in satellite-mediated QKD systems, and countermeasures that can be taken against this, and related methods, of disruption.
Quantum Key Distribution (QKD) is a potential mitigation against quantum computation advances that threaten currently deployed public key cryptosystems. QKD is also a precursor to large-scale quantum communications and the quantum internet. Terrestrial direct transmission of quantum photonic signals is restricted by optical fibre exponential absorption, hence space-based systems have been proposed for intercontinental distribution of quantum keys with lower-loss free-space transmission through vacuum. However, challenges remain for the practical deployment of satellite QKD (SatQKD) such as weather, background light, and terminal deployment. In particular, the short transmission time inherent in low Earth orbit satellite QKD and finite statistical uncertainty can limit secure key generation. Here we illustrate the analysis of these effects and some practical engineering design and operational constraints on key length using the Satellite Quantum Modelling and Analysis (SatQuMA) software package being developed for satellite quantum communications research.
In quantum key distribution (QKD) single-photon transmissions generate the shared, secret random number sequences, known as cryptographic keys that are used to encrypt and decrypt secret communications. Because the security of QKD is based on principles of quantum physics an adversary can neither successfully tap the key transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed an experimental QKD system that uses the four-state BB84 protocol with non-orthogonal photon polarization states and lowest-order adaptive optics to generate shared key material over multi-kilometer atmospheric, line-of-sight paths. I will present results of a daylight demonstration of this system. Key material is built up using the transmission of a photon-pulse per bit of an initial secret random sequence. I will describe the design and operation of the system, present an analysis of the system's security, efficiency, error rate, and secret key rate, as well as cryptographic testing of the key bits produced. I will describe the prospects for longer-distance applications of free-space QKD, particularly for satellite communications.
Quantum key distribution (QKD) enables tap-proof exchange of cryptographic keys guaranteed by the very laws of physics. One of the last remaining roadblocks on the way towards widespread deployment of QKD is the high loss experienced during terrestrial distribution of photons, which limits the distance between the communicating parties. A viable solution to this problem is to avoid the terrestrial distribution of photons via optical fibers altogether and instead transmit them via satellite links, where the loss is dominated by diffraction instead of absorption and scattering. First dedicated satellite missions have demonstrated the feasibility of this approach, albeit with relatively low secure key rates. In order for QKD to become commercially viable, the design of future satellite missions must be focused on achieving higher key rates at lower system costs. Current satellite missions are already operating at almost optimal system parameters, which leaves little room for enhancing the key rates with currently deployed technology. Instead, fundamentally new techniques are required to drastically reduce the costs per secret bit shared between two distant parties. Entanglement-based protocols provide the highest level of security and offer several pathways for increasing the key rate by exploiting the underlying quantum correlations. In this contribution, we review the most relevant advances in entanglement-based QKD which are implementable over free-space links and thus enable distribution of secure keys from orbit. The development of satellite missions is notoriously lengthy. Possible candidates for a new generation of quantum payloads should therefore be scrutinized as early as possible in order to advance the development of quantum technologies for space applications.
Satellite based quantum key distribution (QKD) enables the delivery of keys for quantum secure communications over long distances. Maturity of the technology as well as industrial interest keep increasing. So does the technology readiness of satellite free-space optical communications. A satellite QKD system comprises a quantum communication subsystem and a classical communication subsystem (public channel). Both are implemented with free-space optics. Thus, in satellite QKD system design, there are strong synergies that should be exploited as much as possible and lead to an all-optical satellite QKD system. In this paper, we present a system like this locating all optical channels in ITU DWDM C-band. We focus on the overall conceptual design and the setup of the optical channels for quantum and classical signal transmission. The system description addresses the breadboards of a transmitter laser terminal (Alice terminal), a receiver laser terminal, (Bob terminal), the public channel implementation, the interfaced QKD system and the deployed encryption system. The design basis for the Alice terminal is the laser terminal development OSIRISv3. The design basis for the Bob terminal is the ground station development THRUST. The later contains an adaptive optics correction to enable single mode fiber coupling. This enables the interfacing to almost arbitrary quantum receivers such as the Bob modules used in the described experiment. The public channel is composed of a bi-directional 1 Gbps IM/DD system and a MODEM that implements a proprietary waveform optimized for free-space channels. The system was experimentally analyzed in a field test in the framework of the German initiative QuNET which addresses the use case of quantum secure communication for authorities. The results of the experiment are used to model a feasible LEO satellite-ground link. Performance indicators such as quantum bit error rate and secure key rate of a potential mission are estimated analytically.