Hacking Alice's box in continuous-variable quantum key distribution

Abstract

Security analyses of quantum cryptographic protocols typically rely on certain conditions; one such condition is that the sender (Alice) and receiver (Bob) have isolated devices inaccessible to third parties. If an eavesdropper (Eve) has a side-channel into one of the devices, then the key rate may be sensibly reduced. In this paper, we consider an attack on a coherent-state protocol, where Eve not only taps the main communication channel but also hacks Alice's device. This is done by introducing a Trojan horse mode with low mean number of photonsn which is then modulated in a similar way to the signal state. First we show that this strategy can be reduced to an attack without side channels but with higher loss and noise in the main channel. Then we show how the key rate rapidly deteriorates for increasing photonsn, being halved at long distances each timen + 1 doubles. Our work suggests that Alice's device should also be equipped with sensing systems that are able to detect and estimate the total number of incoming and outgoing photons.

Composable security for continuous variable quantum key distribution: Trust levels and practical key rates in wired and wireless networks

“…More generally, we can assume that Eve is able to detect the leakage from setups [42][43][44]. Here we consider this potential problem for the receiver's setup, so that the fraction 1 − η eff of the photons missed by the detection is stored by Eve and becomes part of her attack.…”

Laser-Damage Attack Against Optical Attenuators in Quantum Key Distribution

“…The attenuation then reverts back to the initial state within minutes. It is however still possible for Eve to exploit this temporary decrease in attenuation, leaking parts of the secret key [11,[33][34][35][36]. This vulnerability window then exists only for a limited time after the high-power exposure.…”

“…However, if the optical attenuation component itself can be altered and its attenuation decreased, either permanently or temporarily, the assumption about the mean photon number may be broken. Eve can then compromise the security of the QKD system [33][34][35][36]. In particular, even a very small increase of the mean photon number requires a correction to the secret key rate in decoy-state BB84 and MDI QKD protocols, otherwise the key becomes insecure [36].…”

Practical Security Analysis of Reference Pulses for Continuous-Variable Quantum Key Distribution

“…Besides, Pereira et al . consider an attack on a coherent-state protocol; Eve not only taps the main communication channel but also hacks AliceâĂŹs device 40 . Nevertheless, there are some defects in theoretical analysis and it is hard to achieve.…”