Laser-seeding Attack in Quantum Key Distribution

For effective quantum communication, the security of the photon source is particularly important in the era of measurement-device-independent quantum key distribution (MDI-QKD) and twin-field QKD (TF-QKD). In practice, the security of the source can still be cracked by an adversary. This study experimentally demonstrates 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 yields increased intensities of the prepared states. Theory shows that the unnoticed intensity increase compromises the security of the prepare-and-measure decoy-state BB84 and MDI-QKD protocols.