# Evaluating the Efficiency of Physical and Cryptographic Security Solutions for Quantum Immune IoT
## 8 Conclusions  
Approaches for physical layer security provide an interesting research field producing solutions that complement security applications and protocols that have so far been based purely on cryptography. For instance, in the post-quantum era, physical layer security may have a role in replacing the public-key algorithms that have been shown as vulnerable against quantum computer assisted cryptoanalysis. In particular, the exchange of cryptographic keys for wireless communication might be based on eavesdropping-resistant secrecy coding.  
We compared physical and cryptographic key exchange approaches by focusing on IoT scenarios and energy efficiency. Our simulation results indicate that our physical layer secrecy coding approach is very competitive in IoT scenarios with short range wireless communication. We also observed that the energy costs both in physical layer and crypto solutions are divided asymmetrically between Alice and Bob, transmitter and receiver. This has implications on the design of security solutions for power-restricted devices. IoT security architectures should support role assignments, where the heavier role is given for access points. This is, unfortunately, not always feasible. However, for scenarios where IoT devices have sufficient antenna and/or random number generation capabilities, role assignments can be used as an advantage.  
The model-based simulation approach proved to be a flexible way to evaluate the energy efficiency of security solutions. It is useful both when designing new algorithms--as it enables evaluations on platforms for which there are no working ported implementations--and when designing platforms as the effects of design decisions can be studied cost-effectively.  
In this study, we focused on a few prominent approaches. For instance, for the crypto part, we focused on the lattice-based approaches NewHope and Frodo, as they have recently gained a lot of attention. However, there exist other post-quantum security implementations targeted for IoT devices, including lattice-based crypto ([PERSON], 2016; [PERSON], 2016; [PERSON], 2016; [PERSON], 2016) and multivariate crypto ([PERSON], 2016; [PERSON], 2016). Furthermore, the efficiency of the NIST candidate proposals for post-quantum cryptography needs to be addressed. Studying the energy efficiency of these other approaches is left for future work. Future work also includes studying the synergies between physical and cryptographic security approaches. More work is also needed to understand what other ways there are for these research fields to better complement each other. For instance, it is important to understand how to incorporate cryptographic authentication efficiently to physical layer security, or how physical layer security can provide an additional confidentiality layer or support authentication with location specific information.  
This work was funded by VTT's Cyber Security and Future Communications Growth Area programs. The authors wish to thank [PERSON], [PERSON], [PERSON], [PERSON], and anonymous reviewers for their helpful comments and feedback.  
[PERSON] analysed threats and cryptographic solutions as well as participated to the design of experiments. He was also the main contributor for the introduction, discussion and conclusions sections. [PERSON] analysed physical-layer security solutions and provided the secrecy coding implementation. [PERSON] modelled the solutions for the simulator and performed the experiments. [PERSON] participated in the design of the work and supported the writing.  
The authors declare no conflict of interest.