Sego is a hypervisor-based system that gives strong privacy and integrity guarantees to trusted applications, even when the guest operating system is compromised or hostile. Sego verifies operating system services, like the file system, instead of replacing them. By associating trusted metadata with user data across all system devices, Sego verifies system services more efficiently than previous systems, especially services that depend on data contents. We extensively evaluate Sego's performance on real workloads and implement a kernel fault injector to validate Sego's file system-agnostic crash consistency and recovery protocol.

InkTag is a virtualization-based architecture that gives strong safety guarantees to high-assurance processes even in the presence of a malicious operating system. InkTag advances the state of the art in untrusted operating systems in both the design of its hypervisor and in the ability to run useful applications without trusting the operating system. We introduce paraverification, a technique that simplifies the InkTag hypervisor by forcing the untrusted operating system to participate in its own verification. Attribute-based access control allows trusted applications to create decentralized access control policies. InkTag is also the first system of its kind to ensure consistency between secure data and metadata, ensuring recoverability in the face of system crashes.

We present the design, security proof, and implementation of an anonymous subscription service. Users register for the service by providing some form of identity, which might or might not be linked to a real-world identity such as a credit card, a web login, or a public key. A user logs on to the system by presenting a credential derived from information received at registration. Each credential allows only a single login in any authentication window, or epoch. Logins are anonymous in the sense that the service cannot distinguish which user is logging in any better than random guessing. This implies unlinkability of a user across different logins. We find that a central tension in an anonymous subscription service is the service provider's desire for a long epoch (to reduce server-side computation) versus users' desire for a short epoch (so they can repeatedly "re-anonymize" their sessions). We balance this tension by having short epochs, but adding an efficient operation for clients who do not need unlinkability to cheaply re-authenticate themselves for the next time period. We measure performance of a research prototype of our protocol that allows an independent service to offer anonymous access to existing services. We implement a music service, an Android-based subway-pass application, and a web proxy, and show that adding anonymity adds minimal client latency and only requires 33 KB of server memory per active user.

Server applications must process requests as quickly as possible. Because some requests depend on earlier requests, there is often a tension between increasing throughput and maintaining the proper semantics for dependent requests. Operating system transactions make it easier to write reliable, high-throughput server applications because they allow the application to execute non-interfering requests in parallel, even if the requests operate on OS state, such as file data.