Laser-seeding Attack in Quantum Key Distribution

Abstract

Quantum key distribution (QKD) based on the laws of quantum physics allows the secure distribution of secret keys over an insecure channel. Unfortunately, imperfect implementations of QKD compromise its information-theoretical security. Measurement-device-independent quantum key distribution (MDI-QKD) is a promising approach to remove all side channels from the measurement unit, which is regarded as the "Achilles' heel" of QKD. An essential assumption in MDI-QKD is however that the sources are trusted. Here we experimentally demonstrate that a practical source based on a semiconductor laser diode is vulnerable to a laser seeding attack, in which light injected from the communication line into the laser results in an increase of the intensities of the prepared states. The unnoticed increase of intensity may compromise the security of QKD, as we show theoretically for the prepare-and-measure decoy-state BB84 and MDI-QKD protocols. Our theoretical security analysis is general and can be applied to any vulnerability that increases the intensity of the emitted pulses. Moreover, a laser seeding attack might be launched as well against decoy-state based quantum cryptographic protocols beyond QKD.

Attacking quantum key distribution by light injection via ventilation openings

“…Light coming from the wrong direction in the normal QKD optical channel can also alter the intended operation of the system. For instance, external laser light can alter the photon sources in QKD devices and has been shown to weaken security either by seeding the source laser so that consecutive pulses are not phase-independent [ 75 ], altering the wavelength to identify the state choice [ 76 , 77 ], increasing the mean photon number [ 23 , 60 , 77 ], or performing laser machining to physically alter the components inside the QKD setup [ 26 , 61 ]. In this paper, we have focused on light entering from unsuspected places, such as ventilation openings.…”

“…However a system using BB84 for long-distance transmission might also be vulnerable to light injection attacks. It has been shown that even a small unexpected increase of the output mean photon number may break the security of decoy-state BB84 and measurement-device-independent QKD protocols [60], which are often used at longer distances. While the known combined photon-number-splitting and cloning attacks [58] require a quantum memory, the difference between the assumed and the actual key rates opens a loophole in the security of the system and must be fixed.…”

Practical security of continuous-variable quantum key distribution with reduced optical attenuation

“…Our results show that the channel excess noise may be underestimated by Alice and Bob under the effects of decreased optical attenuation. Subsequently, the secret key rate is overestimated by Alice and Bob, which is coincident with the security analysis arXiv:1904.08777v1 [quant-ph] 17 Apr 2019 result of DVQKD under the effects of reduced optical attenuation [35]. Thus, the decrease of optical attenuation may open a security loophole for Eve to successfully hide her attacks, such as the classical non-Gaussian attack, i.e., the interceptresend attack.…”

Optical designs for realization of a set of schemes for quantum cryptography

“…In case of four laser setting, the wavelength control using external laser Lee et al (2017) is successfully implemented, which can be circumvented using a circulator to stop Eve from sending strong beam to the sources. Independently, single laser settings are also attacked using laser seeding and injection locking Huang et al (2019) but circulator will work against these attacks as well. Further, encoding devices can also be attacked using Trojan-horse pulses, which back-reflect from various optical elements revealing information of the sender Gisin et al (2006).…”