Quantum hacking of a continuous-variable quantum-key-distribution system using a wavelength attack

Abstract

The security proofs of continuous-variable quantum key distribution are based on the assumptions that the eavesdropper can neither act on the local oscillator nor control Bob's beam splitter. These assumptions may be invalid in practice due to potential imperfections in the implementations of such protocols. In this paper, we consider the problem of transmitting the local oscillator in a public channel and propose a wavelength attack which can allow the eavesdropper to control the intensity transmission of Bob's beam splitter by switching the wavelength of the input light. Specifically we target continuous-variable quantum key distribution systems that use the heterodyne detection protocol using either direct or reverse reconciliation. Our attack is proved to be feasible and renders all of the final key shared between the legitimate parties insecure, even if they have monitored the intensity of the local oscillator. To prevent our attack on commercial systems, a simple wavelength filter should be randomly added before performing the monitoring detection.PACS numbers:

Trusted Noise in Continuous-Variable Quantum Key Distribution: A Threat and a Defense

“…The role of other practical imperfections in coherent-state CV QKD was analyzed by Jouguet et al [109], who studied the imperfect realistic Gaussian modulation, the calibration of the detectors and the trusted phase noise in the sender station, and it was shown that these effects should be taken into account in the security analysis, especially in the finite-size regime. It was also shown that CV QKD systems can be in principle compromised using a wavelength attack on the local oscillator in the heterodyne [110,111] and homodyne [112] detection, which can be however prevented by spectral filtering or real-time monitoring of shot noise [113], the latter being also useful against the calibration attacks on the clock pulses in coherent-state CV QKD [114]. Furthermore, the fluctuations of the local oscillator were shown to be potentially harmful in CV QKD [115], which can be compensated by tuning and monitoring of the intensity of the local oscillator by the trusted parties [116].…”

Continuous-variable quantum key distribution with a leakage from state preparation

“…On the other hand, an eavesdropper can implement so-called Trojan horse attacks in order to get information about the modulator settings from the backreflected light [3] or use state preparation and encoding flaws in DV QKD protocols [4,5] as well as benefit from information leakage, e.g., from auxiliary degrees of freedom of carrier states [6]. Continuous-variable (CV) QKD protocols (see [7] for reviews), based on the homodyne detection, can be robust against blinding, but are potentially vulnerable to other practical attacks, such as a wavelength attack on the homodyne detector [8] or continuous-variable counterpart of Trojan horse attacks [9].…”

“…Trusted parties can then identify possible sources of side information available to an eavesdropper, and take them into account in security analysis. In the field of CV QKD this included consideration of already mentioned specific detection attacks [8,13] , analysis of source imperfections [14][15][16][17], and role of multimode structure of state preparation and detection [18]. Trusted device imperfections may be under partial control of an eavesdropper so that an output of internal loss in a device may contribute to eavesdroppers knowledge on the raw key though information leakage (side-channel loss) or so that the noise imposed by trusted device imperfections may be controlled by an eavesdropper to corrupt the data (side-channel noise).…”

Quantum Cryptography: Key Distribution and Beyond

“…However, continuous-variable quantum key distribution is not immune to all possible side channel attacks, and various strategies to perform side channels attacks have been discussed in the recent past (cf. [349,357,368] and references therein).…”