Overview
TOKYO--Toshiba Corporation, a leading innovator in technologies realizing quantum key distribution (QKD) for secure network communications, has announced two significant advances in essential technologies for establishing global-scale quantum networks: Large-Scale Quantum Key Distribution Network Control Technology, and High-Speed Quantum Key Distribution Technology.
A QKD network is structured into two layers: the Key Management Layer responsible for key management and key distribution route control, and the Quantum Layer, which manages the distribution of quantum keys. Large-Scale QKD Network Control Technology enhances key distribution efficiency in the Key Management Layer, while High-Speed Quantum Key Distribution Technology accelerates key distribution in the Quantum Layer. These technologies will realize faster distribution of keys with higher capacities, and more secure quantum cryptography communications over a wider area. These advances enable the transmission of larger volumes of keys at higher speeds, thereby expanding the reach and operability of quantum communications.
The QKD network is a platform that enables encrypted communications by securely sharing quantum keys across multiple sites in a network of QKD systems. The Key Management Layer ensures the efficient relay of quantum keys through designated sites, which enables secure communications between sites that are not directly linked by QKD systems (Figure 1).
Toshiba’s Large-Scale QKD Network Control Technology integrates an autonomous key data transfer control function at every site in the Key Management Layer, alongside an optimized control function of stored number of key data managed by a centralized server. This combination ensures efficient key distribution and optimal distribution of quantum keys shared throughout the network. Separately, in the Quantum Layer, High-Speed Quantum Key Distribution Technology uses a newly developed optical wavelength multiplexing device to distribute quantum keys from multiple QKD systems over a single optical fiber, which enhances speed and realizes distribution of higher capacity quantum keys.
In the development of Large-Scale QKD Network Control Technology, Toshiba used a simulated QKD network with 16 sites to successfully demonstrate optimal key distribution. For the High-Speed Quantum Key Distribution Technology, three QKD systems were bundled and operated in a laboratory environment using a 45 km fiber, a configuration that significantly improved key distribution speed: from approximately 0.9 Mbps with one system to approximately 2.3 Mbps with the multiplexed systems (*1).
The details of this technology and the research results were presented at QCrypt 2024 (the14th International Conference on Quantum Cryptography), a global conference held from September 2–6. Part of this research and development was supported by the Ministry of Internal Affairs and Communications (MIC), R&D of ICT Priority Technology Project (JPMI00316) “R&D for construction of a global quantum cryptography network”.
Development background
QKD technology leverages the properties of quantum mechanics to realize inherently secure communications resistant to eavesdropping. Today’s networks constantly handle highly confidential data, and preparing for potential cyber-attacks is more critical than ever. There is also the threat of ‘harvest now, decrypt later’—the interception of data today for future decryption with advanced quantum computers. Quantum cryptographic communication technology is expected to answer these concerns by offering secure communications for the foreseeable future, supported by global research and technology evaluation (*2, *3).
In order for quantum cryptographic communication technology to be brought into diverse fields in a secure, global network that goes beyond cities and countries, construction of a large-scale quantum key distribution network is essential (*3). This requires enhanced control systems for scaling up QKD networks, and QKD systems to support high-capacity, high-speed encrypted communications. In a QKD network of multiple QKD systems, secure communications between any two sites in the network is realized by relaying a quantum key from one to the other. As Figure 1 shows, a quantum key relayed from site X to site Z may have to pass through intermediate sites, such as site Y. In this process, optimization of key relay routes and the number of keys to be relayed across the entire QKD network are critical for the effective functioning of the network.
Beyond this, meeting global-level demand for cryptographic keys requires faster key distribution by every system in the network.
Features of the technology
Large-Scale QKD Network Control Technology optimizes relays within the QKD network and stored number of quantum keys at each site (Figure 2). It enhances quantum key transfer efficiency by providing autonomous control of key transfers on each site, which optimizes transmission routes for quantum key relays, and by using an index calculated from the number of cryptographic keys stored in the QKD link to determine the next hop site. Modifications to standard routing algorithms, such as OSPF (*4) and BGP (*5), enable autonomous and optimal routing control, with consideration for the availability of quantum keys on each QKD link.
A centralized server manages the identification of suitable exchange partners and the determination of quantum key exchange quantities for all sites in the network by aggregating data on key requests and usage history from each site. The sites then use information supplied by the server, plus application-specific key requests, to optimize selection of exchange partners and the number of quantum keys to exchange.
The system secures flexibility in handling network failures and variations in quantum key availability on QKD link by integrating autonomous and distributed data transmission route control technologies into centralized management of key exchange coordination. This allows it to balance scalability across numerous network locations with optimal responsiveness to application demands. The technology’s core functionalities were verified on the simulated QKD network with 16 sites, using virtual servers, software to replicate QKD operations, and key management software. Future development will focus on evaluation and refinement for larger networks.
High-Speed Quantum Key Distribution Technology integrates optical wavelength multiplexing, server virtualization, and key integration control to combine multiple QKD systems into a single system, thus enhancing overall key distribution speed. Newly developed optical wavelength multiplexing devices were used to integrate three QKD systems, each operating on a different wavelength, and they were managed over the same pair of optical fibers typically used by a single QKD system. Server virtualization consolidated control functions for the three QKD systems onto a single physical server.
Demonstrations confirmed that quantum keys generated by the three virtualized QKD systems were delivered to the key management server in the same way as those from a single QKD system, facilitated by the newly developed key integration control function (Figure 3). The setup (*7) achieved a key distribution speed of 2.3 Mbps by using a pair of optical fibers, the same configuration as a single full QKD system. This corresponds 80% of the total key distribution speed for three systems operating independently, demonstrating that, despite some additional overhead from multiplexing, the virtualized QKD systems deliver a significant acceleration in key distribution speed. This approach is also scalable, and further speed improvements can be expected from incorporating additional QKD devices.
Future developments
Toshiba will continue to advance research and development of quantum technologies, including quantum cryptography, and their application in diverse sectors including healthcare, finance, government, and communications infrastructure. Through its efforts, Toshiba aims to contribute to a safe, secure future.
- The average speed of QKD measured during a continuous operation experiment for approximately one week in an environment using 45 km of spool fiber in a laboratory.
- https://www.global.toshiba/ww/technology/corporate/rdc/rd/topics/22/2212-01.html
- https://www.global.toshiba/ww/technology/corporate/rdc/rd/topics/22/2202-01.html
- https://www.global.toshiba/ww/technology/corporate/rdc/rd/topics/20/2007-02.html
- OSPF: Open Shortest Path First. A major optimization algorithm for routing paths in a network.
- BGP: Border Gateway Protocol. An optimization algorithm for transmission routes in a network, primarily used for inter-domain route control when constructing large-scale networks.
- Three quantum key distribution systems, one physical server, and one optical wavelength multiplexer on both the transmitter and receiver sides.