# QuietPlace: An Ultrasound-Based Proof of Location Protocol with Strong Identities
## 9 Discussion, Conclusions, and Future work  
In this paper, we described the participating entities, the malicious users and common attacks in proof of location protocols. We presented the characteristics of PoL protocols and thoroughly examined the problem of strong identities, proposing a novel solution. We identified and solved the technical challenges we faced. We later introduced QuietPlace, a proof of location protocol that is based on ultrasound communication and provides unforgeable, private proofs that support strong identities. Ultrasound makes it difficult to carry messages over long distance without having to convert them to another form. This makes man-in-the-middle attacks more difficult to succeed, as the additional delay can be easily observed. The cryptographic techniques that we proposed separate knowledge between CA and verifier. The CA validates the user identities while the verifier validates the location of the prover of concern. In this way, the credibility of the users is maintained without sacrificing privacy. We also analyzed the security and privacy performance of QuietPlace, comparing it with other protocols in literature. By proving the physical user's location using audio/video capture on the prover device, we managed to solve the problem of multiple devices that carry the same user's credentials. To the best of our knowledge, this is the first attempt of a proof of location protocol to provide a complete solution to this issue. It is left for future research work to enhance the current implementation with a medium access control protocol, as messages are broadcasted via ultrasound and collisions may occur. Also, in order to start the procedure, the witness listens until it receives a PR message from a prover. This is something which can be further extended in order to increase privacy considerations for the user of the mobile phone. Apart from solving the above issues, the CA and verifier can be implemented on a server instead of being emulated on the prover's device. Also, we would like to experiment with ultrasound communication, so that bigger range, smaller directionality, and more throughput is achieved. Manually configuring liquid-dsp could be the first step. Finally, it is important that more compact message encoding is being used, so that it takes less time for the protocol execution to be completed. In general, the way the CA can evaluate the behavior of the participants is of great scientific interest. Figure 9: Screenshots of our prototype application: (**a**) The home-screen, used to retrieve the location of the device; (**b**) The protocol control screen. To sum up, the scope of this study has been (as a first step) to develop a PoL protocol that can tackle most (if not all) security and privacy vulnerabilities that can appear in other PoL mechanisms. As it has been presented in Section 7.2, QuietPlace seems to cover these security and privacy threats of interest in a sufficient manner. The first steps towards implementation of the protocol and testing of the requirements and performance on the physical layer have already been taken, as presented in Section 8. Aspects like performance, execution time, code/encoding optimization, and time and space complexity of the algorithm are out of the scope of this study per se and are the primary subject for future research and work for the further enhancement of the protocol. Conceptualization, D.K., O.V., A.L., and T.V. ; Formal analysis, D.K. and A.L. ; Funding acquisition, A.L. ; Investigation, G.P. ; Methodology, D.K., O.V., G.P., and A.L. ; Project administration, A.L. and T.V. ; Software, D.K. and O.V. ; Supervision, A.L. and T.V. ; Validation, D.K. and G.P. ; Writing--original draft, D.K., O.V., and A.L. ; Writing--review and editing, O.V., G.P., A.L., and T.V. The authors collaborated on all sections of the paper and all authors participated in all writing and revising. All authors have read and agreed to the published version of the manuscript.