An investigation of jamming in free-space quantum key distribution

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.