Robustness of Optical Steganographic Communication Under Coherent Detection Attack

In fiber-optic networks, optical steganographic communication hides the existence of stealth signals in public channels. The previous security analyses assumed threat models in which eavesdroppers rely only on the real-time key search in the optical domain for signal recovery. In this letter, we study a new threat model that uses coherent detection and offline digital signal processing (DSP) to recover the stealth signal, and we show the robustness of optical steganographic communication under this attack. We find that eavesdroppers equipped with the state-of-the-art coherent detectors and DSP technologies fail to estimate the secret key. In addition, even if the eavesdroppers are given the secret key, the stealth signal cannot be recovered from the signal using DSP. The histogram of the received signal after DSP displays a noise-like form which prevents eavesdroppers from detecting the existence of the stealth signal. We attribute the system robustness to the unique features of using amplified spontaneous emission noise as the signal carrier, including wide bandwidth, large phase variance, and fast phase fluctuation.