# Key Recovery for Content Protection Using Ternary PUFs Designed with Pre-Formed ReRAM
## 7 Summary and Future Research  
The analysis reported in this paper show that the proposed ReRAM based solutions outperform SRAM PUF-based schemes in terms of BERs and tamper resistance. Bit error rates below the \(10^{-3}\) range were demonstrated in the keys generated from ReRAMs operating in the pre-forming range with the differential cell pairing protocol. Unlike with SRAMs, such low BERs do not necessitate lengthy enrollments to remove the unstable cells. The differential protocol keeps only those pairs of cells with resistances further apart from each other. The BERs are reduced when the proportion of pairs that are masked by the protocol is large enough. Low BERs enable the use of a small search engine, the RBC-light, as a replacement for power-consuming error-correcting schemes, without fuzzy extraction, and without data helpers. The combination of tamper resistance, low BERs, and low power correcting methods facilitated the development of an end-to-end cryptographic system to deliver and protect digital files. Future work: Unlike SRAM PUF based solutions, which are commercially available, and which have solid performances, the deployment of schemes using pre-formed ReRAMs requires additional research, that is not underestimated by the authors. We intend to perform exhaustive characterizations of BERs of the ReRAMs, with additional enrollment cycles, extended temperature cycles in the \(-40\)\({}^{\circ}\)C to \(+140\)\({}^{\circ}\)C range, increased buffer sizes of the number of pairs, and accelerated aging cycles. As the expected BERs will be in the \(10^{-6}\) to \(10^{-10}\) range, the experiments will need to run for months in order to produce statistically valid results. The cryptographic protocols and the software driving the schemes require further optimization to enhance security and mitigate various cyber-attacks. We are also aware of the need to involve independent third-party investigators to identify potential weaknesses in the proposed methods. The methods presented in this paper could be considered for the following applications:  
* Per paid content delivery. A service provider can deliver several encrypted files containing information such as movies, music, apps, maps, and operating systems. The user obtains access to the files after paying a fee. * Protected user manuals. Staged access to a prepared set of instructions for a particular task, which evolves over time, due to changes in conditions. The users receive, as needed, access codes to open a particular portion of a user manual. An example of such an application would be pilots flying a plane. * Cooperative users. The server concurrently sends to user 2 the information needed by user 1 to retrieve a sub-key, and to user 1 the information needed by user 2 to retrieve the complementary sub-key. The full key is generated by knowledge of both sub-keys. * Securing interconnected IoTs. Nodes of IoTs such as controlling and metering elements in a grid, home hubs, smart sensors, contain information that is stored locally and which needs to be protected constantly. * Authentication of the server. When operating in a zero-trust environment, the server sends users information previously used to encrypt and store a session key. Conceptualization, and methodology, B.F.C. and S.J. ; software, S.J. ; validation, formal analysis, and investigation, B.F.C. and S.J. ; resources, B.F.C. ; data curation, B.F.C. and S.J. ; writing--original draft preparation, B.F.C. and S.J. ; writing--review and editing, B.F.C. and S.J. ; visualization, supervision, project administration, and funding acquisition, B.F.C. All authors have read and agreed to the published version of the manuscript. This research was funded by the United States Air Force Research Laboratory (AFRL) of Rome, New York, contract number 19-0437 of the Broad Agency Announcement number FA8750-19-S-7003. **Acknowledgments:** The authors thank their research partners at Northern Arizona University for their support, in particular [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON].