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<p>With the recent trend toward open architectures in optical communication networks, the risk of physical eavesdropping on secret keys and data has increased. In particular, the growing adoption of reconfigurable optical add-drop multiplexing nodes and spatial multiplexing technologies, such as multicore fibers, has highlighted the eavesdropping risks posed by physical factors such as crosstalk. In this study, as part of efforts to enhance security in physical layer encryption technologies, a model was developed to evaluate the leakage of encrypted data and keys in digital coherent communication using phase encryption. This model assumes simultaneous crosstalk attacks on ciphertext and side-channel attacks on encryption keys by an eavesdropper and assesses the information recovery potential when the eavesdropper partially acquires secret key information, using normalized generalized mutual information (NGMI) as a measure. Simulations were conducted to evaluate the effectiveness of phase encryption on Nyquist dual-polarized <i>M</i>-level quadrature amplitude modulation signals, examining the decoding characteristics on the eavesdropper’s side based on variations in wiretap ratio and block lengths. The results confirmed that an increase in the wiretap ratio led to a rise in NGMI obtained by the eavesdropper, with the NGMI surpassing the forward error correction limit at certain signal-to-noise ratio (SNR) levels in the case of a 99% wiretap ratio. However, in higher SNR regions, the phase shift of the encrypted symbols caused the noise distribution of the failed eavesdropped symbols to deviate from the typical noise, increasing noise variance and reducing the NGMI. Furthermore, error-correcting codes using soft-decision decoding were evaluated to mitigate information leakage while preserving encryption characteristics, and significant improvement in error rates at low SNRs was observed with concatenated coding schemes. These findings suggest that the random nature of physical layer encryption can effectively suppress information leakage under specific conditions, providing insights for improving encryption methods and decryption models to prevent eavesdropping in future optical communication networks.</p>

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Impact of physical layer attacks on phase-encrypted optical signals in coherent communication systems

  • 期刊论文

  • 发表日期：

    2025年12月5日

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  • Keiji Shimada,
  • Takahiro Kodama

摘要

With the recent trend toward open architectures in optical communication networks, the risk of physical eavesdropping on secret keys and data has increased. In particular, the growing adoption of reconfigurable optical add-drop multiplexing nodes and spatial multiplexing technologies, such as multicore fibers, has highlighted the eavesdropping risks posed by physical factors such as crosstalk. In this study, as part of efforts to enhance security in physical layer encryption technologies, a model was developed to evaluate the leakage of encrypted data and keys in digital coherent communication using phase encryption. This model assumes simultaneous crosstalk attacks on ciphertext and side-channel attacks on encryption keys by an eavesdropper and assesses the information recovery potential when the eavesdropper partially acquires secret key information, using normalized generalized mutual information (NGMI) as a measure. Simulations were conducted to evaluate the effectiveness of phase encryption on Nyquist dual-polarized M-level quadrature amplitude modulation signals, examining the decoding characteristics on the eavesdropper’s side based on variations in wiretap ratio and block lengths. The results confirmed that an increase in the wiretap ratio led to a rise in NGMI obtained by the eavesdropper, with the NGMI surpassing the forward error correction limit at certain signal-to-noise ratio (SNR) levels in the case of a 99% wiretap ratio. However, in higher SNR regions, the phase shift of the encrypted symbols caused the noise distribution of the failed eavesdropped symbols to deviate from the typical noise, increasing noise variance and reducing the NGMI. Furthermore, error-correcting codes using soft-decision decoding were evaluated to mitigate information leakage while preserving encryption characteristics, and significant improvement in error rates at low SNRs was observed with concatenated coding schemes. These findings suggest that the random nature of physical layer encryption can effectively suppress information leakage under specific conditions, providing insights for improving encryption methods and decryption models to prevent eavesdropping in future optical communication networks.