Research and Development

Theme and summary

We have developed a continuous-variable (CV) QKD system and an optical secure communication system, and performed field demonstration of combined network of CV-QKD and optical secure communication. Since both CV-QKD and optical secure communication systems exploit devices that are based on the same operating principle as the coherent optical communication, it is expected that a combined network system will enable secure and safe communication infrastructure that can offer diverse functions ranging from unconditionally secure communications to high-speed and high-secure data transmission in a unified way. We executed the following three subthemes.

Subtheme C-1: CV-QKD system
The CV-QKD system developed in the project is capable of transmitting 50 kbps over a 10 km optical fiber. The system has been tested in a field experiment. In the security analysis, the effect of optical losses and excess noise are taken into account to estimate the information leaked to the eavesdropper and privacy amplification is applied to generate secret keys that is secure against entangling cloner attack.
Subtheme C-2: Optical secure communication system
The optical secure communication system is based on the combination of QAM technologies and stream cipher. By choosing a physically different 2-dimensional set of QAM signals using stream cipher, an enhanced security of physical-layer encryption is achieved. We have developed an optical secure communication system operating over 320 km with speeds of 20 – 60 Gbits/s.
Subtheme C-3: Integration technologies
In order to realize technologies for integrating CV-QKD and optical secure communication into coherent optical communication, we developed low noise and high speed QAM systems. Field demonstration of a combined network of CV-QKD and optical secure communication was performed in which secure keys are supplied from the CV-QKD system to the QAM quantum noise stream cipher (QNSC) system. We also demonstrated wavelength-division-multiplexing of CV-QKD and QAM/QNSC.

Activities

Task title Outcome Date Note
Long distance CV-QKD prototype Stable operation of four-state CV QKD over 40 km fiber is realized by utilizing single-path interferometer. Mar. 2012 Qcrypto2012
Security analysis of four-state CV-QKD Secret key rate against entangling cloner attack is calculated. Mar. 2012 Proceeding of QIT 27, p.182-185
Off-line operation of optical secure communication Proof of principle experiment of two-dimensional cryptography has been successfully conducted. Mar. 2012  
Demonstration of 2.5 Gsymbol/s, 16 QAM two-dimensional optical secure communication over 160 km fiber. Mar. 2013  
Low excess noise operation of CV-QKD Utilizing dispersion compensation method, reduction of excess noise in long distance CV-QKD is achieved. Sep. 2012 Student presentation award at the JPS autumn meeting 2012.
High speed CV-QKD system 10 MHz operation using a commercially available balanced receiver. Mar. 2013  
FPGA development system based controller has been fabricated. Mar. 2013  
Executable modules for error correction and privacy amplification are tested. Jul. 2013  
Real-time optical secure communication 10 Gbps FPGA-based encryption device has been fabricated. Mar. 2013  
Automated operation of CV-QKD Realtime stabilization of relative phase between the signal and LO pulse is achieved. Mar. 2014 SPIE Security + Defence 2016
Automated generation of secure keys by high speed CV-QKD system using a PC program is achieved. Mar. 2014  
Networked operation of CV-QKD system The CV-QKD system is installed in the Tokyo QKD network and securer keys are uploaded to the network. Mar. 2014 Qcrypt 2105
On-line operation of optical secure communication Real-time 10 Gbit/s-16 QAM quantum stream cipher transmission over 320 km with FPGA-based transmitter and receiver Mar. 2014 OFC2015
Real-time adaptive 4-64 QAM, 20-60 Gbit/s quantum noise stream cipher transmission over 320 km with FPGA-based transmitter and receiver Sep. 2015 ECOC2015
Combined network of CV-QKD and QAM/QNRC CV-QKD and QAM/QNSC systems are connected by a common interface and key supply function is installed. Mar. 2014  
An online QNSC transmission using secret keys generated by CV-QKD is demonstrated. Mar. 2015  

Details

Figure 1

QNSC
Receiver QNSC
Transmitter CV-QKD
Transmitter CV-QKD
Receiver blacket image Control PCs

Fig. 1CV-QKD system and optical secure communication system

Both the CV-QKD system and QAM/QNSC system are packaged in 19 inch racks. PCs are used to control the transmitter and receiver. Secure keys generated by the CV-QKD system are supplied to the QAM/QNSC system in an on-line manner.

Details

With the progress of coherent optical communication technologies for a high-speed and large-capacity communication system, there is an increasing interest in physical layer security protocols using common techniques such as quadrature amplitude modulation and homodyne detection of coherent light. It is expected in future that an all-in-one sending and receiving equipment offers a full range of secure communication within a tradeoff between the security and speed: by just switching its operation mode, unconditionally secure metro communication and physically secure core communication, and also computationally secure high-speed communication may be possible.

We have developed a CV-QKD prototype capable of generating secure keys at 50 kbps over a 10 km optical fiber. We have also developed an optical secure communication system based on the combination of QAM technologies and stream cipher. By choosing a physically different 2-dimensional set of QAM signals using stream cipher, an enhanced security of physical-layer encryption is achieved. We have demonstrated QAM/QNSC transmission over 320 km with a speed of 20 – 60 Gbit/s. Then, field demonstration of a combined network of CV-QKD and optical secure communication was performed in which secure keys are supplied from the CV-QKD system to the QAM/QNDC system.

We will proceed with the following plan for the development and dissemination of research and development results.