Multi-Layer QCA Shift Registers and Wiring Structure for LFSR in Stream Cipher with Low Energy Dissipation in Quantum Nanotechnology
Round 1
Reviewer 1 Report
The work titled "Multi-layer QCA Shift Registers and Wiring Structure for LFSR in Stream Cipher with Low Energy Dissipation in Quantum Nanotechnology" holds significance within the field of circuit design. It serves as an initial step towards the development of low-power shift registers for stream ciphers in the realm of Quantum-dot Cellular Automata (QCA). Nevertheless, there are opportunities for enhancing the article's clarity and originality.
The introduction should offer a more comprehensive portrayal of the current state of shift register design within the QCA domain for stream ciphers. This contextualization is vital to underscore the work's significance. The author might consider incorporating a table or figure summarizing the state-of-the-art in QCA-based shift register designs for stream ciphers. Such an addition would facilitate readers in grasping the context surrounding the proposed work.
The article's drawbacks are as follows:
Noise poses a substantial challenge in QCA, with the potential to disrupt shift register operations. The article falls short in addressing how the proposed design will contend with noise-related issues.
The article restricts its focus to a 4-bit shift register. It is imperative to examine how the proposed design can be scaled up to accommodate larger shift registers.
Author Response
1. Noise poses a substantial challenge in QCA, with the potential to disrupt shift register operations. The article falls short in addressing how the proposed design will contend with noise-related issues.
(A) Noise related issues in QCA circuit design were expressed in terms of signal stability. This has a high relationship with the energy dissipation rate, which directly affects signal stability and circuit operation. The study also identifies the wiring problem that arises as the number of bits increases in linear structures, and determines how much energy consumption can be reduced by solving this problem.
2. The article restricts its focus to a 4-bit shift register. It is imperative to examine how the proposed design can be scaled up to accommodate larger shift registers.
(A) I think the modularity and scalability of the proposed structure are well addressed in the paper. Since there was only a problem with CLK's input wiring, the problem was solved by introducing a multi-layer wiring structure in Section 4.2.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this paper, structural characteristics and problems of existing various types of SRs are presented, and new multi-layered serial-in serial-out and parallel-in parallel-out SRs are proposed. The whole study is systematic and the data is solid. I would recommend the acceptance of current work if the following issues can be addressed:
1. The novelty of this manuscript is not clear enough. The authors should further highlight the novelty.
2.The quality of some figures is not high. The authors should further improve the quality of figures for this manuscript.
Author Response
1. The novelty of this manuscript is not clear enough. The authors should further highlight the novelty.
(A) The novelty of the proposed research is the easy conversion of serial and parallel input and output in a multi-layer structure and the proposal of a multi-layer wiring technique.
2.The quality of some figures is not high. The authors should further improve the quality of figures for this manuscript.
(A) Regarding the part you mentioned, we will adjust the resolution to suit the editor's needs when editing the paper.
Author Response File: Author Response.pdf
Reviewer 3 Report
Overall the paper is well written.
Can the author also explain the physics of each state in figure 3, for e.g. how is a null cell activated and how is it propagated from one cell to another physically?
The above explanation will help the readers better appreciate the paper.
Author Response
1. Can the author also explain the physics of each state in figure 3, for e.g. how is a null cell activated and how is it propagated from one cell to another physically?
The above explanation will help the readers better appreciate the paper.
(A) When an input value enters an input cell, neighboring cells are sequentially activated according to the clock state.
Author Response File: Author Response.pdf
Reviewer 4 Report
- The author could compare the proposed SR structures to the following state-of-the-art SR structures: Multiplexer-based SR, Configurable SR, and Asynchronous SR.
- The proposed SR structures may exhibit performance degradation at high clock frequencies.
- LFSRs are often used in stream ciphers to generate pseudorandom sequences. The proposed SR structures could be used to improve the performance of stream ciphers in terms of speed, security, and power consumption. However, there is no investigation in terms of speed and security.
- The author did not evaluate the proposed SR in a real-world setting. It is possible that the proposed SR may not perform as well in practice as they do in simulation.
- The author should have discussed the overhead of using the proposed SR. For example, the SR may require more complex clocking circuitry than existing SRs.
- What happens as the number of bits in the LFSR increases?
- How robust are the proposed SR structures to noise and other disturbances?
- It is important to consider potential weaknesses and limitations to provide a balanced view of the research.
- Cryptographic applications heavily rely on the security of pseudorandom number generators. Discussing how the proposed changes in SR structures affect the cryptographic properties of the generated pseudorandom numbers is beneficial.
- The manuscript needs to discuss potential challenges and limitations that might arise when implementing the proposed multi-layered SR structures in real-world scenarios.
- It is important to consider the long-term reliability and robustness of the proposed solutions, especially in cryptographic applications where the hardware may be in use for an extended period.
- The author mentions that the proposed SRs show performance improvement regarding area-time complexity, design cost, and energy dissipation. However, he did not specify the specific metrics used for these comparisons. Without this information, it's challenging for readers to gauge the significance of the improvements.
Author Response
1. The author could compare the proposed SR structures to the following state-of-the-art SR structures: Multiplexer-based SR, Configurable SR, and Asynchronous SR.
(A) In the proposed study, most of the latest QCA-based SR structures were compared diligently.
2. The proposed SR structures may exhibit performance degradation at high clock frequencies.
(A) Please understand that the simulation of the proposed study was conducted in a clock environment as mentioned in Section 4.
3. LFSRs are often used in stream ciphers to generate pseudorandom sequences. The proposed SR structures could be used to improve the performance of stream ciphers in terms of speed, security, and power consumption. However, there is no investigation in terms of speed and security.
(A) To check the speed, please check the latency in the performance comparison. Additionally, the proposed research involves designing the physical hardware structure and security is not a consideration.
4. The author did not evaluate the proposed SR in a real-world setting. It is possible that the proposed SR may not perform as well in practice as they do in simulation.
(A) Many researchers engaged in related research are putting a lot of effort into ensuring that QCA-based structural design can be performed well in the real world.
5. The author should have discussed the overhead of using the proposed SR. For example, the SR may require more complex clocking circuitry than existing SRs.
(A) The proposed structure is designed as a multi-layer structure, so there may be overhead compared to the existing single-layer circuit. Therefore, when calculating the cost, the overhead of the multi-layer structure was considered as shown in equation (3). In addition, the overhead for cell interaction-based Mux and 5-input majority voting gate was also considered.
6. What happens as the number of bits in the LFSR increases?
(A) The proposed structure has excellent modularity and scalability and can be easily expanded. There is simply a problem with the signal stability of input wiring such as the CLK input line. Therefore, in this study, we proposed a multi-layer wiring technique and confirmed that not only signal stability but also energy dissipation rate can be significantly reduced.
7. How robust are the proposed SR structures to noise and other disturbances?
(A) Noise related issues in QCA circuit design were expressed in terms of signal stability. This has a high relationship with the energy dissipation rate, which directly affects signal stability and circuit operation. The study also identifies the wiring problem that arises as the number of bits increases in linear structures, and determines how much energy consumption can be reduced by solving this problem.
8. It is important to consider potential weaknesses and limitations to provide a balanced view of the research.
(A) It is clear that the proposed multi-layer wiring technique helps maintain clock and signal status of long input wiring. However, additional experiments and confirmation are needed to determine whether a stable condition can be guaranteed for a much longer wire, and another alternative is needed to ensure the stability of clocks and signals, and continuous research on this is required.
9. Cryptographic applications heavily rely on the security of pseudorandom number generators. Discussing how the proposed changes in SR structures affect the cryptographic properties of the generated pseudorandom numbers is beneficial.
(A) The proposed structure is a study on next-generation quantum circuits, which are in the spotlight as alternative circuits that can replace the problems of existing CMOS circuits. The proposed research was proposed to change the physical characteristics of the existing research, and the logical structure is the same. In other words, it is difficult to believe that the proposed research will have any impact on the cryptographic properties of pseudorandom numbers.
10. The manuscript needs to discuss potential challenges and limitations that might arise when implementing the proposed multi-layered SR structures in real-world scenarios.
(A) In order to implement the proposed research in a real environment, QCA's clock routing system is being considered, but the current research progress is that it is very difficult to consider this in the multi-layer QCA circuit design. As research on multi-layer structures has recently become active, continued research on multi-layer clock routing systems is necessary.
11. It is important to consider the long-term reliability and robustness of the proposed solutions, especially in cryptographic applications where the hardware may be in use for an extended period.
(A) The long-term reliability and robustness of the proposed structure appear to be very closely related to signal stability and energy dissipation rate, and it is believed that research on this should continue.
12. The author mentions that the proposed SRs show performance improvement regarding area-time complexity, design cost, and energy dissipation. However, he did not specify the specific metrics used for these comparisons. Without this information, it's challenging for readers to gauge the significance of the improvements.
(A) Area-time complexity, design cost, and energy dissipation are all simulated and measured values based on the same environment and simulation parameters mentioned in Section 4.1.
Author Response File: Author Response.pdf
Reviewer 5 Report
The paper present new structures for LSFR based on multy-layer QCA. The LSFR is proposed because an important part of the pseudo-random number generators. The proposed structures are compared to what is already present in literature. The comparison is based on several “quality” parameters that highlight weakness and strengths of each of them. Simulations are performed to show the structures functionality. In conclusion the proposed structures compares well to the others and present several vantages (and some disadvantage).
The paper, in general, is clear, well written and of potential interest for journal readers.
I have only minor comments:
-L56-58. Not clear. Please rephrase.
-L97. Two points: “..”
-L200-202. In lists of elements probably “;” should be substituted by “:”
-L213: in [40], not “Reference [40]”
I found the english basically correct.
Author Response
I have only minor comments:
1. L56-58. Not clear. Please rephrase.
(A) It was modified as follows. “The study also identifies the wiring problem that arises as the number of bits increases in linear structures, and determines how much energy consumption can be reduced by solving this problem.”
2. -L97. Two points: “..” -L200-202. In lists of elements probably “;” should be substituted by “:”, -L213: in [40], not “Reference [40]”
(A) They have corrected.
Author Response File: Author Response.pdf
Round 2
Reviewer 4 Report
The manuscript can be accepted in the present form.
