Quantum Communication Rsearch Center

Y-00 quantum stream cipher communication system

The mission of this research center is to pioneer revolutionary technologies that surpass current cutting-edge information technologies, such as optical communications and ultra-high-speed computing. To achieve this, we aim to transform new principles and methodologies derived from quantum information theory into practical technologies that benefit industry and society.
In particular, we are advancing the systemization of the Y-00 quantum stream cipher and developing security evaluation devices to support its practical implementation.

Primary Research Topic

1．Enhancing the Performance of Y-00 Quantum Stream Cipher

Following the development of a 1 Gbps Y-00 quantum stream cipher transceiver, we are currently working on a 10 Gbps Y-00 quantum stream cipher communication system. Ensuring security while maintaining high-speed performance requires innovative circuit design and strong theoretical support. To meet these demands, we are developing countermeasures such as the nonlinearization of pseudo-random number generators.
Additionally, due to insufficient uniformity in circuits that map data onto multilevel bases, we propose a novel randomization method and aim to implement it. Furthermore, we are improving the proof methodology for the necessary and sufficient conditions of the second-generation Y-00 quantum stream cipher that remains secure even if the key is stolen, and we are working toward its practical implementation.

2．Performance Evaluation and Enhancement Technologies for Y-00 Quantum Stream Cipher Transceiver

In collaboration with domestic and international companies, we are conducting experimental research to apply first-generation Y-00 devices to optical fiber communication systems, such as gigabit Ethernet (1 Gbps). We also conduct various performance evaluation experiments to demonstrate Y-00's strong security features.
Furthermore, we are conducting high-speed transmission experiments targeting 10 Gbps or higher. We are exploring the limits of speed and capacity using technologies such as optical time-division multiplexing and wavelength-division multiplexing. In addition, we are designing and prototyping a second-generation Y-00 quantum stream cipher communication system with enhanced security. Research has also begun on network topologies to support future deployment.

3．Additional Randomization Schemes in Y-00 Quantum Stream Cipher Communication Systems

A practical quantum optical communication cryptographic system can be realized by incorporating appropriate randomization techniques into its theoretical base model. Although several randomization methods have been proposed to date, most assume a phase-modulation-based quantum optical cryptographic model as their foundation.
In contrast, the intensity-modulation-based quantum optical cryptography being developed at our university exhibits a certain degree of asymmetry in its signal constellation, which differs fundamentally from phase modulation. Therefore, when developing randomization techniques for intensity-modulation-based systems, accounting for this signal asymmetry is expected to yield further improvements.
To this end, we are focusing on the development of randomization methods specifically tailored to intensity-modulation-based quantum optical cryptography. Additionally, we examine various known attacks on conventional stream ciphers and assess their applicability to quantum optical cryptography through theoretical analysis and computer simulations. Under attack scenarios that cannot be ruled out, we conduct security evaluations of the proposed randomization techniques.