This paper considers an application of the quantum stream cipher (QSC) Y-00. QSC Y-00 can provide secure long-haul and high-capacity data transmission in optical networks. Post-quantum cryptography (PQC) can provide quantum-resistant authentication and key-establishment. We propose a secure link architecture for optical communication networks using QSC Y-00 and PQC. Further, we report a field experiment using the optical fibers embedded along a railway truck between two train stations to demonstrate user authentication, key-establishment, and secure data communication with the intensity modulation-based Y-00 transceivers and PQC. Finally, we discuss the further applications of the proposed secure link architecture.
This study demonstrates the optical fiber transmission of the Y-00 quantum stream cipher with quantum deliberate signal randomization (QDSR). QDSR is a deliberate signal randomization driven by a quantum random number generator, which substantially enhances signal masking using quantum noise to realize higher security. A 10-Gb/s line-rate dualpolarization phase-shift keying Y-00 cipher with QDSR is transmitted over a 400-km field-installed single-mode fiber link with optical amplifiers. When the phase levels after encryption and the index of QDSR are set to 216 and 0.2, respectively, the quantum noise masking number increases by a factor of more than 40 compared to that without QDSR, which enhances security. However, the transmission penalty owing to QDSR remains small.
Security enhancement is a major challenge in future 6G wireless networks. In this study, we have introduced a symmetric-key encryption system, which utilizes multilevel signaling, for the security of microwave signals against wireless interception. The system achieves quantum-noise signal masking at microwave frequencies via optical-tomicrowave frequency conversion based on the homodyne process, thus providing high signal security. We show experimental demonstrations of quantum-noise randomized phase-shift keying modulation/quadrature amplitude modulation cipher generation at a frequency of ~GHz via the intensity modulation/direct detection analog intermediate frequency over fiber transmission. The proposed system simultaneously achieves microwave signal delivery over a fiber link and signal encryption based on sufficient quantum-noise signal masking for wireless communication systems.
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.
KEYWORDS: Transceivers, Signal detection, Interference (communication), Binary data, Signal to noise ratio, Computer security, Quantum communications, Modulation, Sensors, Signal generators
As a security parameter of Y-00 quantum stream cipher, a guessing probability by an eavesdropper for a secret key of legitimate users is discussed. Assuming that Eve employs the direct detection and Gaussian intensity distribution of each intensity level of Y-00 cipher signals are same, an analytic solution of probability of correct guessing of the secret key in a case of the ciphertext-only attack is derived. The solution is applied to experimentally measure the probabilities of our Y-00 quantum stream cipher transceiver. A very low probability of the Y-00 cipher transceiver is experimentally confirmed.
A power distribution of optical signals as the ciphertext of Y-00 quantum stream cipher transceivers should be uniform,
even when the bit sequence of plaintext is a non-uniform sequence. For examining the uniformity, we experimentally
measure powers of optical signals with 4096 intensity levels and calculate the ratio of signal numbers over and under the
average power. The ratios for various kinds of bit sequences are 0.5 with measurement error of 1%, which is an evidence
of the uniformity of the power distribution. In addition, the effectiveness of a randomization technique of overlapping
selection keying for enhancing the security against the known plaintext attack is experimentally observed.
Deployment of digital coherent transmission technologies to metro networks drives the use of higher-order modulation formats such as PDM-16QAM and downsizing of optical transceivers. A narrow-linewidth (<300 kHz) tunable laser with high output power (>+17 dBm) is very attractive for such purposes, not only because it can compensate for the modulation loss increase caused by a high-peak-to-average ratio of the electrical driving signal of higher-order modulation formats, but also because it can be shared between transmitter and receiver saving the foot-print and power dissipation. This paper reviews the Tunable Distributed Amplification — Chirped Sampled Grating — Distributed Reflector (TDA-CSG-DR) laser being developed for metro application.
We introduce parametric tunable dispersion compensation scheme that has strong advantages in operating bandwidth and
tuning response. The parametric tunable dispersion compensator (P-TDC) using highly-nonlinear fiber with a low
dispersion slope achieves wide grid-less operating bandwidth of more than 1 THz and fast tuning responses of a few tens
of microseconds. We also develop the setup of the P-TDC for practical usage, utilizing polarization diversity scheme.
Field transmission using the polarization-insensitive P-TDC is also successfully demonstrated.
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