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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Quantum hacking: how Eve can exploit component imperfections to control yet another of Bob's single-photon qubit detectors

Sébastien Sauge, Vadim Makarov, Andrey N. Anisimov

Published Jun 1, 2009• 1 citation
Publisher

Abstract

In this study, we investigated several possible attacks that an eavesdropper could launch against cryptosystems equipped with yet another commonly used silicon photon counting detector module operating with active quenching and manufactured by Perkin Elmer (model SPCM-AQR). We showed that when the avalanche photo-diode (APD) of the detector gets illuminated with bright optical pulses (instead of single photons), the voltage at which the APD is biased drops by more than 12-14 V if the repetition rate of the bright pulses is large enough (above 70kHz here).

DOI
10.1109/cleoe-eqec.2009.5192723

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In this study, we investigated several possible attacks that an eavesdropper could launch against cryptosystems equipped with yet another commonly used silicon photon counting detector module operating with active quenching and manufactured by Perkin Elmer (model SPCM-AQR). We showed that when the avalanche photo-diode (APD) of the detector gets illuminated with bright optical pulses (instead of single photons), the voltage at which the APD is biased drops by more than 12-14 V if the repetition rate of the bright pulses is large enough (above 70kHz here).
We control using bright light an actively-quenched avalanche single-photon detector. Actively-quenched detectors are commonly used for quantum key distribution (QKD) in the visible and near-infrared range. This study shows that these detectors are controllable by the same attack used to hack passively-quenched and gated detectors. This demonstrates the generality of our attack and its possible applicability to eavsdropping the full secret key of all QKD systems using avalanche photodiodes (APDs). Moreover, the commercial detector model we tested (PerkinElmer SPCM-AQR) exhibits two new blinding mechanisms in addition to the previously observed thermal blinding of the APD, namely: malfunctioning of the bias voltage control circuit, and overload of the DC/DC converter biasing the APD. These two new technical loopholes found just in one detector model suggest that this problem must be solved in general, by incorporating generally imperfect detectors into the security proof for QKD.
We control using bright light an actively-quenched avalanche single-photon detector. Actively-quenched detectors are commonly used for quantum key distribution (QKD) in the visible and near-infrared range. This study shows that these detectors are controllable by the same attack used to hack passively-quenched and gated detectors. This demonstrates the generality of our attack and its possible applicability to eavsdropping the full secret key of all QKD systems using avalanche photodiodes (APDs). Moreover, the commercial detector model we tested (PerkinElmer SPCM-AQR) exhibits two new blinding mechanisms in addition to the previously observed thermal blinding of the APD, namely: malfunctioning of the bias voltage control circuit, and overload of the DC/DC converter biasing the APD. These two new technical loopholes found just in one detector model suggest that this problem must be solved in general, by incorporating generally imperfect detectors into the security proof for QKD.
We control using bright light an actively-quenched avalanche single-photon detector. Actively-quenched detectors are commonly used for quantum key distribution (QKD) in the visible and near-infrared range. This study shows that these detectors are controllable by the same attack used to hack passively-quenched and gated detectors. This demonstrates the generality of our attack and its possible applicability to eavsdropping the full secret key of all QKD systems using avalanche photodiodes (APDs). Moreover, the commercial detector model we tested (PerkinElmer SPCM-AQR) exhibits two new blinding mechanisms in addition to the previously observed thermal blinding of the APD, namely: malfunctioning of the bias voltage control circuit, and overload of the DC/DC converter biasing the APD. These two new technical loopholes found just in one detector model suggest that this problem must be solved in general, by incorporating generally imperfect detectors into the security proof for QKD.
Single photon detectors (SPDs) based on passively quenched avalanche photodiodes can be temporarily blinded by relatively bright light, of intensity less than 1 nW. A bright-light regime suitable for attacking a quantum key distribution system containing such detectors is described in this paper. In this regime, all SPDs in the receiver Bob are uniformly blinded by continuous illumination coming from the eavesdropper Eve. When Eve needs a certain detector in Bob to produce a click, she modifies the polarization (or other parameters used to encode quantum states) of the light she sends to Bob such that the target detector stops receiving light, while the other detector(s) continue to be illuminated. The target detector regains single photon sensitivity and, when Eve modifies the polarization again, produces a single click. Thus, Eve has full control of Bob and can perform a successful intercept–resend attack. To check the feasibility of the attack, three different models of passively quenched detectors have been tested. In the experiment, I have simulated the intensity diagrams the detectors would receive in a real QKD system under attack. Control parameters and side effects are considered. It appears that the attack could be practically possible.
Quantum cryptography has been developed from being a theoretical proposal to having real world applications, with companies developing and selling quantum key distribution (QKD) instruments commercially. Although laws of quantum physics guarantee perfect security in the key distribution protocol, several vulnerabilities in the practical implementations have been described and demonstrated. In some of these attacks the eavesdropper has been able to acquire the entire secret key without being detected by the two communicating parties. This thesis describes an experimental setup for automatically characterizing and damaging single photon avalanche photodiodes using a high power laser to damage the diode with the intention to find new weaknesses in QKD systems. Hopefully, the discovery of loopholes will stimulate the researchers and commercial manufacturers to fix their implementations, leading to more secure systems. For a silicon avalanche photodiode (APD) in a passive-quenching circuit, a number of interesting results have been found. It has been shown that we are able to change many of the APDs key characteristics by applying strong illumination. We have been able to reduce the dark count rate of several APDs by up to 80% in a predictable way by strong laser illumination, an effect which is believed to be caused by localized annealing. This is an interesting result not only in the field of quantum cryptography, but perhaps also for improving the manufacturing process of different semiconductor components. Other parameters that have been found to change in interesting ways are the dark current and the breakdown voltage. It has been demonstrated that these changes may compromise the security of QKD systems.
It has previously been shown that the gated detectors of two commercially available quantum key distribution (QKD) systems are blindable and controllable by an eavesdropper using continuous-wave illumination and short bright trigger pulses, manipulating voltages in the circuit [Nat. Photonics 4, 686 (2010)]. This allows for an attack eavesdropping the full raw and secret key without increasing the quantum bit error rate (QBER). Here we show how thermal effects in detectors under bright illumination can lead to the same outcome. We demonstrate that the detectors in a commercial QKD system Clavis2 can be blinded by heating the avalanche photo diodes (APDs) using bright illumination, so-called thermal blinding. Further, the detectors can be triggered using short bright pulses once they are blind. For systems with pauses between packet transmission such as the plug-and-play systems, thermal inertia enables Eve to apply the bright blinding illumination before eavesdropping, making her more difficult to catch.