Research and Development


To establish secure photonic network using QKD technology, QKD system needs to continuously generate crypto-key at a high speed and low cost under ensured security. On the other hand, enhancement of application based on QKD system is also necessary. To achieve the above purposes, we set following two subthemes.

Subtheme 1: Stabilization technique
We proposed a new and efficient key distillation algorithm by improving the existing security proofs of quantum cryptography. We also implemented it as a software and are demonstrating its performance; particularly the speed and the stability.
Subtheme 2: Enhancing application platform
Our aim is to develop new mobile phone software on Android® Devices which enables secure communication between smart phones using keys shared by QKD. This application makes eavesdropping on calls impossible by using One-Time Pad Encryption. In addition, we carry out field tests of this application to verify the operational stability.


Subtheme 1: Stabilization technique
We developed a new and high-speed key distillation software for quantum cryptography. We are continuing to demonstrate its performance within the Tokyo QKD Network, i.e., by distilling sifted keys from the DPS-QKD device on a real-time basis.
Subtheme 2: Enhancing application platform
We ported the "One-Time Pad mobile phone system" which is developed before this project to Android® Devices, and implemented a key acquisition functionality based on common interface for key supplying from QKD examined with NEC. Furthermore, to make calls of this system more stable, we evaluated call quality in the field test and confirmed sufficient quality of calls within cellphone range.

Detail or activities

Subtheme 1: Stabilization technique
"High-speed and stable key distillation software"
Fully software-based implementation
Applied theoretical outcome of "Subject 157B-T01"
Real-time basis key distillation
Subtheme 2: Enhancing application platform
"One-Time Pad mobile phone system"
Implemented as Android® smartphone application
OTP keys are supplied to mobile phones by using common interface
Sufficient quality of calls within cellphone range
Figure 1

area highlite  Subtheme 2   Subtheme 1 

Fig. 1System overview


Final results for Team 157A-T01

Task title Outcome Date Note
1: High-speed and stable key distillation software Improved key rates by improved security analysis (Finite size analysis, hash function) Sep. 2012

Jun. 2013
NJP 14 (2012) 093014
IEEE Trans. IT 59, 4700 (2013)
Fully software-based key distillation (EC with HARQ, PA with FFT algorithm ) Mar. 2012 ISEC2010-121
Software implementation for DPS-QKD Mar. 2014  
Real-time basis key distillation for DPS-QKD Mar. 2015  
2: One-Time Pad mobile phone system Conceptual design Mar. 2013  
Ported software to Android® OS Oct. 2013 prototype
Design common key supply interface Oct. 2013 examined with NEC
Stabilized quality of calls within cellphone range Mar. 2014  
Confirmed sufficient quality of calls within cellphone range Mar. 2015  


Subtheme 1: Stabilization technique
"Efficient key distillation algorithm"
Our results verified that the entire process of the key distillation can actually be performed solely by a software on a PC, although it had previously been thought to require a dedicated hardware such as FPGA boards. We hope to apply these results to other QKD devices, such as the BB84 by NEC and the CVQKD by Gakushuin Univ.
Subtheme 2: Enhancing application platform
"Development of mobile phone software"
We developed a new mobile phone software which makes eavesdropping on communication impossible using QKD. Furthermore, we examined a common interface for supplying keys to a software from a QKD with NEC, and implemented a key acquisition functionality in our software based on this interface. Our future issues are both to establish methods of measuring communication disruption to clarify the condition of good call quality, and to extend applicability of this system other than to mobile phones.