Eavesdropping on Key Distribution Scheme based on Shot Noise of Intense Laser Pulses

StÉPhane Félix, Nicolas Gisin, André Stefanov +1 more

Marcin Jarzyna, Michał Jachura, Konrad Banaszek

Intensity modulation/direct detection (IM/DD) optical key distribution (OKD) is a method to generate a secret key whose security against passive eavesdropping is guaranteed by the shot noise inherent to the photodetection process. Here the effects of intensity-dependent symbol shape distortion on the IM/DD OKD security are investigated assuming that the eavesdropper can implement temporal mode demultiplexing using e.g. the quantum pulse gating technique. The quantitative analysis includes key generation based on either hard- or soft-decoding of the detected signal as well as the impact of excess detection noise. A simple, rule-of-thumb relation between the severity of the symbol shape distortion and the signal strength required to ensure key security is presented.

Tatsuya Tomaru

Andrew Funk, Michael G. Raymer

We propose a scheme for quantum key distribution using macroscopic nonclassical pulses of light having of the order ${10}^{6}$ photons per pulse. Sub-shot-noise quantum correlation between the two polarization modes in a pulse gives the necessary sensitivity to eavesdropping that ensures the security of the protocol. We consider pulses of two-mode squeezed light generated by a type-II seeded parametric amplification process. We analyze the security of the system in terms of the effect of an eavesdropper on the bit error rates for the legitimate parties in the key distribution system. We also consider the effects of imperfect detectors and lossy channels on the security of the scheme.

Yijia Zhao, Yichen Zhang, Song Yu +2 more

The shot-noise unit (SNU) is a crucial factor for the practical security of a continuous-variable quantum key distribution system. In the most widely used experimental scheme, the SNU should be calibrated first and used as a constant during key distribution. Because the measurement result of quadrature is normalized with the calibration SNU but scaled with practical SNU, which could open loopholes for the eavesdropper to intercept the secret key. In this paper, we report a quantum hacking method to control the practical SNU by using the limited compensation rate for polarization drift. Since the polarization of local oscillator pulses is partially measured, the attack is implemented by manipulating the polarization of the local oscillator pulses without measurement when the system is running. The simulation and experiment results indicate that the practical SNU can be manipulated by the eavesdropper. By making the difference between the calibration and the practical SNU, the excess noise estimated by Alice and Bob could always be lower than the practice which is introduced by the eavesdropper and the distributed keys are not secure.

Hasnaa Hajji, M. El Baz, Walter O. Krawec