Quantum Key Distribution Networks: Challenges and Future Research Issues in Security

Round 1

Reviewer 1 Report

I have included my points in the attached reviewer report. 

Comments for author File: Comments.pdf

Author Response

Q1. The authors could briefly present in subsection 2.2 the research trends in the development of the next generation of quantum communication systems and protocols with improved performance (link distances, higher key rates). As an example, the recently proposed twin-field QKD (TF-QKD) effectively overcomes the key capacity limitation without quantum relay and achieves long-distance quantum key distribution.

Work:  We truly appreciate the reviewer for pointing out this important issue. The revised manuscript has added a brief explanation about TF-QKD and cited its relevant studies for improving the completeness of the survey on the development of the next generation of quantum communication systems and protocols. The modifications made in this revised manuscript can be found in Line 167 to 170.

 Q2. On the same subsection, coexistence schemes based on the transmission of both classical/quantum links over the shared fibers can be also discussed. From a deployment-perspective, this approach could significantly reduce the installation costs for additional fiber links. Several experiments demonstrating the classical/QKD coexistence can be used in this part to discuss also this direction pursued from the research community.

Work: We added some descriptions in subsection 2.2 for introducing the technology that transmits both classical and quantum messages over the shared fibers. Furthermore, we also addressed the benefit of the technology. We truly appreciate the reviewer for pointing out this important issue. This part of modifications can be found in the revised manuscript in Line 150 to 154.

 Q3. The authors present the active optical switch networks as candidates to realize a QKD network. Some references of experiments/demonstrators should be included in this subsection, to briefly present the switching mechanisms proposed for these nodes and the physical layer challenges associated with these nodes (e.g., additional photon loss).

Work: We sincerely thank the reviewer for this comment that makes the content of our research become more complete. The physical layer challenges are added in the revised manuscript to briefly describe the impact of qubit communication caused by the imperfect optical switch, and some related references have also been cited. The modification made in this revised manuscript can be found in Line 189 ~ 194.

Q4. Addressing the P2MP mechanisms in QKD networks is one of the major challenges towards the Next Generation of QKD networks. Aside from the QCKD protocol, the authors could also consider in their discussion some of the well-known physical layer concepts that have been proposed to tackle this challenge. For example, the TDM-based multiuser implementation [Townsend, P.D. Nature 1997, 385, 47–49] has been recently presented as an indicative P2MP technology which can be used for ultra-dense QKD networks where multiple users will be served with acceptable secret key rates [D. Zavitsanos et al, Appl. Sci. 2020, 10(15)].

Work: We truly appreciate the reviewer for pointing out this important issue. In the revised manuscript, we have discussed to use the physical layer concepts to tackle this P2MP challenge. Some related references have also been cited. On the other hand, we took the concept of TDM-based multiuser scheme as another important solution to allow a node to efficiently distribute the secret key to multiple nodes. The modification made in this revised manuscript can be found in line 339 ~ 343.

Q5. The authors could discuss in more detail their view on PQC-based security interface between the Quantum nodes and the end user/applications. Some recently demonstrated developments assisting in this direction can be also included in this subsection, emphasizing also on the challenges related to the PQC/QKD integration.

Work: Thank you for this valuable comment that make the content of our manuscript more complete. We added an explanation about the usages of PQC between the quantum node and the classical end user/application. In addition, the challenge related to the PQC/QKD integration is described and existing research works are cited. The modifications made in this revised manuscript can be found in Line 420 ~ 424 and 435~442.

Q6. The authors should combine the figure captions in one single part in Figure 3, to avoid the use of text/sentences in the figure.

 

Work: Thank you for this comment. Figure 3 has been modified and another similar case in Figure 4 has also been taken care of in the revised manuscript.  

Reviewer 2 Report

At line 235-237 add a reference for this statement.

For the sake of clarity, I would suggest putting line 343 and line 345 as separate formulas and thus showing the associative properties of XOR function, like (A XOR (B XOR C) =  (A XOR B) XOR C), etc.

Please correct formatting from pages 4 -16.

Author Response

Q1. At line 235-237 add a reference for this statement.

Work: Thank you for this valuable comment. Several relevant references have been added into the revised manuscript.

Q2. For the sake of clarity, I would suggest putting line 343 and line 345 as separate formulas and thus showing the associative properties of XOR function, like (A XOR (B XOR C) = (A XOR B) XOR C), etc. The modification made in this revised manuscript is in line 361 ~ 366.

Work: Thank you for this valuable comment. The description in line 343 and 345 of the original manuscript has been modified depending on your suggestion.

Q3. Please correct formatting from pages 4 -16.

Work: Thank you for your comments. The format of the whole paper has been corrected and modified carefully in the revised manuscript.