Cryptanalysis of Practical Optical Layer Security Based on Phase Masking of Mode-Locked Lasers and Multi-Homodyne Coherent Detection

Abstract

We have previously suggested a promising approach for optical layer security, incorporating an all-optical spectrum spreading, spectral phase-encoding time-spreading, and noise-protected coherent communication system. An authorized receiver with the spectral phases key can evoke a multi-homodyne coherent detection (MHCD) to reconstruct the noise-submerged signal. Unless deciphered in real-time, by all-optical means and with the correct phases key mask, an adversary cannot reconstruct the transmitted data, which is permanently lost. This feature prohibits unauthorized offline processing, regardless of the resources and efforts available to the adversary, thus making data-in-transit record-proof and resilient to any computational power, including the quantum computer. In this work, we present a novel security analysis for this approach, where three different types of attacks are proposed and thoroughly studied: Naive, Analytic, and Greedy. These algorithms represent different approaches for all-optical phases key cracking. We formulated a mathematical model for a Naive attacker who trials an arbitrary phase mask. In the Analytic approach, the attacker studies the encoding system by trialing arbitrary test patterns. In contrast, the attacker who employs the Greedy approach maximizes his performance in each step until the desired signal-to-noise ratio (SNR) level is obtained. We analyze these approaches analytically and discuss their cryptanalysis aspects concerning performance, complexity, and the photonic hardware used to decode the phase mask. Our simulations and models suggest a set of conditions for an all-optical transmission system that is impervious to cryptography attacks.