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IEEE Photonics Technology Letters

Tradeoff Between Reach and Security in Nyquist WDM Transmission of PSK Y-00 Quantum Stream Cipher

Ken Tanizawa, Fumio Futami

Published Aug 18, 2023• 2 citations
Publisher

Abstract

Y-00 quantum stream cipher is a signal-level encryption technique that prevents signal interception in optical fiber communications. Security of the Y-00 cipher depends on the signal power, and thus the cipher system has a tradeoff between the security and signal quality. This letter reports theoretical analysis of Nyquist wavelength-division multiplexed transmission of phase-shift keying Y-00 cipher over a nonlinear fiber channel. A tradeoff formula between reach and signal security is derived utilizing the Gaussian noise model. Numerical study shows that the PSK Y-00 cipher achieves high-capacity ultra-long-haul transmission with a countermeasure against interception.

DOI
10.1109/lpt.2023.3306357

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Y-00 quantum stream cipher is a signal-level encryption technique that prevents signal interception in optical fiber communications. Security of the Y-00 cipher depends on the signal power, and thus the cipher system has a tradeoff between the security and signal quality. This letter reports theoretical analysis of Nyquist wavelength-division multiplexed transmission of phase-shift keying Y-00 cipher over a nonlinear fiber channel. A tradeoff formula between reach and signal security is derived utilizing the Gaussian noise model. Numerical study shows that the PSK Y-00 cipher achieves high-capacity ultra-long-haul transmission with a countermeasure against interception.
A record-long 10,118-km fiber transmission with physical layer encryption is demonstrated utilizing a Y-00 cipher based on signal masking by quantum (shot) noise. The Y-00 cipher enables symmetric-key data encryption to ensure the security of the physical layer of optical communications. Irreducible secrecy without significant negative impact on transmission performance is achieved by the synergistic effect of combining seed-key-based high-order modulation and truly random shot noise inevitable in optical detection. This paper reports a comprehensive study of applying a phase-shift-keying (PSK) Y-00 cipher for ultra-long haul fiber transmission. Theoretical analysis shows that security-enhanced transmission over transoceanic-distance (>10,000 km) fiber is feasible when the quadrature PSK data signal is encrypted by converting to a PSK signal with 218 levels. Subsequently, 10,118-km standard single-mode fiber transmission of 48-Gbit/s line-rate dual-polarization PSK Y-00 cipher with 218 levels is experimentally demonstrated. An adequate signal quality above the Q-factor threshold of soft decision forward error correction is achieved together with sufficient signal masking by shot noise, yielding balanced transmission performance and high security in an ultra-long-haul PSK Y-00 cipher transmission system.
We present a symmetric-key direct data encryption technique utilizing signal masking by quantum noise, called Y-00 quantum stream cipher. Physical encryption of phase-shift-keying (PSK) Y-00 quantum stream cipher is achieved by our proposed extremely high-order phase modulation. Two cascaded phase modulators are driven with two synchronized digital-to-analog converters for coarse-to-fine modulations, resulting in a record 217 phase levels for the quantum noise masking. Decryption of the cipher is implemented in digital signal processing after intra-dyne coherent detection with a free-running local oscillator. We experimentally demonstrate transmission of 10-Gbaud digital-coherent PSK Y-00 cipher with 217 levels over a 240-km field-installed single-mode fiber.
This study proposes an intensity modulation/direct detection intermediate frequency-over-fiber (IFoF) system that generates a microwave orthogonal frequency-division multiplexing (OFDM) quantum-noise randomized phase-shift-keying (PSK) cipher. The system directly prevents wireless interception by an eavesdropper without a private key. We theoretically analyze the system and derive a fundamental tradeoff between the security and signal quality at an intermediate frequency (IF). The system achieves balanced security and signal quality. We experimentally demonstrate 4.09-Gbit/s PSK cipher generation at an IF of 3.6 GHz. The cipher has 216phase levels, and more than 100 adjacent signals are masked by quantum noise. The quantum-noise signal masking imposes irreducible uncertainty on illegitimate reception of the cipher, and a symbol error ratio (SER) that an eavesdropper can reach approaches 1. A lower bound of the SER is promised because truly random signal masking by quantum noise cannot be reduced. The error vector magnitude of the IF signals after decryption is maintained at a low value for wireless transmission. The cipher directly and effectively protects the wireless transmission of personal data from interception.