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.
@article{arxiv.2503.14105,
title = {Quantum Pulse Gate Attack on IM/DD Optical Key Distribution Exploiting Symbol Shape Distortion},
author = {M. Jarzyna and M. Jachura and K. Banaszek},
journal= {arXiv preprint arXiv:2503.14105},
year = {2025}
}