title: Laser damage helps the eavesdropper in quantum cryptography.
abstract: We propose a class of attacks on quantum key distribution (QKD) systems where an eavesdropper actively engineers new loopholes by using damaging laser illumination to permanently change properties of system components. This can turn a perfect QKD system into a completely insecure system. A proof-of-principle experiment performed on an avalanche photodiode-based detector shows that laser damage can be used to create loopholes. After ∼1  W illumination, the detectors' dark count rate reduces 2-5 times, permanently improving single-photon counting performance. After ∼1.5  W, the detectors switch permanently into the linear photodetection mode and become completely insecure for QKD applications.
authors.affiliation: Department of Electronics and Telecommunications, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors.forename: Audun Nystad
authors.initials: AN
authors.lastname: Bugge
authors.affiliation: School of Information and Communication Technology, Royal Institute of Technology (KTH), Electrum 229, SE-16440 Kista, Sweden.
authors.forename: Sebastien
authors.initials: S
authors.lastname: Sauge
authors.affiliation: Department of Science in Engineering, Faculty of Engineering, International Islamic University Malaysia, P.O. Box 10, 50728 Kuala Lumpur, Malaysia.
authors.forename: Aina Mardhiyah M
authors.initials: AM
authors.lastname: Ghazali
authors.affiliation: Department of Electronics and Telecommunications, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors.forename: Johannes
authors.initials: J
authors.lastname: Skaar
authors.affiliation: Department of Electronics and Telecommunications, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors.forename: Lars
authors.initials: L
authors.lastname: Lydersen
authors.affiliation: Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Vadim
authors.initials: V
authors.lastname: Makarov