This project develops the Privacy-preserving Intrusion-resilient Secure Multiparty-computation-based Overlay (PISMO) system for secure and private communication through existing, non-cooperative 5G infrastructure. PISMO transparently integrates into several widely employed commercial end-user applications such as messaging and content sharing via authoring tools, e.g., Microsoft Office, email, and web-browsing. As several military, government, and critical infrastructure operations rely on such end-user applications, PISMO hardens them against threats. Considered threats range from unintended eavesdropping to sabotaging cyber-attacks. This is accomplished while using existing and affordable 5G communication infrastructure without trusting or cooperating with the 5G operator. Deploying and commercializing the PISMO system contributes to achieving greater national security and protection of communication privacy, wherever such operations are carried out, nonetheless always operating in a secure and resilient, yet highly functional and maintainable manner.<br/><br/>The PISMO overlay consists of client software provisioned on 5G end devices and server software deployed in clouds on the Internet to form the backbone of PISMO; clients will connect via the 5G wireless network to the backend servers. The project focuses on use-centric design & usability to converge the developed software components into an easily usable, deployable, and ultimately transitionable system that leverages modern cryptography (e.g., secure multi-party computation, private information retrieval, and identity-based encryption) and advanced resilience and reliability techniques for distributed systems and networks. In this research, two user types are considered; an Administrator, who configures, deploys, monitors, and maintains the PISMO overlay, and an End-User operating the PISMO client on wireless 5G end devices. The research concentrates on solutions to hard questions about configuring, deploying, and managing PISMO via three use cases applicable to (1) critical infrastructure operations, (2) government uses, and (3) military operations. These use cases will lead to precise definitions of the human-facing components and procedures. The project’s scope also considers deploying prototype implementations on testbeds in private and public clouds to perform user studies capturing user experience (UX) elements and features. The prototypes will enable the calibration of various automation opportunities that the system offers in support of the Administrator’s task to define settings and maintain functionality. Lastly, an integrated and deployed prototype solution will meaningfully and practically demonstrate the advances in usability, functionality, resilience, and maintainability that the research in this project provides.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.