Hacking Quantum Key Distribution via Injection Locking

Abstract

Unconditionally secure communication, being pursued for thousands of years, however, hasn't been reached yet due to continuous competitions between encryption and hacking. Quantum key distribution (QKD), harnessing the quantum mechanical nature of superposition and non-cloning, may promise unconditional security by incorporating the one-time pad algorithm rigorously proved by Claude Shannon. Massive efforts have been made in building practical and commercial QKD systems, in particular, decoy states are employed to detect photon-number splitting attack against single-photon source loophole, and measurement-device-independent (MDI) QKD has further closed all loopholes in detection side, which leads to a seemingly real-life application. Here, we propose and experimentally demonstrate an MDI-QKD hacking strategy on the trusted source assumption by using injection locking technique. Eve injects near off-resonance photons in randomly chosen polarization into sender's laser, where injection locking in a shifted frequency can happen only when Eve's choice matches with sender's state. By setting a shifted window and switching the frequency of photons back afterwards, Eve in principle can obtain all the keys without terminating the real-time QKD. We observe the dynamics of a semiconductor laser with injected photons, and obtain a hacking success rate reaching 60.0%. Our results suggest that the spear-and-shield competitions on unconditional security may continue until all potential loopholes are discovered and closed ultimately.QKD is the best-known application of quantum cryptography, capable of distributing secure keys between two communication parties (known as Alice and Bob) in the presence of eavesdroppers (Eve). Both theoretical and experimental accomplishments have been made over the past decades [1][2][3][4], and commercial QKD systems are now available on the market providing enhanced security for communication. Nevertheless, real-life devices are hard to conform with the hypotheses of theoretical security proofs, leading to continuous hacking strategies tar- *

Laser-seeding Attack in Quantum Key Distribution

“…Indeed, this value of injection power has been also confirmed recently by the experimental results shown in Ref. [59], in which Eve's injection power is in 100-160 nW range. We also note that a real QKD system may use a laser diode without the internal isolator, then the injection power used in our laser seeding attack may be reduced to the above level.…”

“…In practice, it is important to note as well that Eve could in principle combine the laser seeding attack with various attacks to enhance her hacking capability, for example, with the laser damage attack [22,24] as mentioned above, with the THA analysed in Refs. [48-50, 53, 72, 73], and/or with the recently introduced injection-locking attack [59]. For instance, Eve could employ the fact that the laser seeding can be affected in real time by the state of Alice's modulator, changing the laser wavelength depending on the modulator setting [59] and/or modulating the intensity multiplication factor κ.…”

“…[48-50, 53, 72, 73], and/or with the recently introduced injection-locking attack [59]. For instance, Eve could employ the fact that the laser seeding can be affected in real time by the state of Alice's modulator, changing the laser wavelength depending on the modulator setting [59] and/or modulating the intensity multiplication factor κ. Besides using her injected light to modify the internal functioning of the transmitter (as done in the laser seeding attack), Eve could also simultaneously perform a THA and measure the back-reflected light to obtain information about the transmitter's settings for each emitted light pulse.…”

“…While preparing this Article for publication, we have learned of another laser seeding experiment that changes the wavelength of Alice's laser rather than its intensity [59].…”

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.…”