Hardware provides driver authors both a strict specification of the operations a driver is allowed to do, and a highly permissive interface full of operations a driver can do. Authoring drivers that adhere to the provided hardware device protocol is challenged by dynamic definitions of what a driver should do based on the hardware's state. This is further complicated by increasingly capable hardware which may transition between states concurrently and independently from the software driver.

Existing end-to-end encrypted systems provide applications with strong privacy and integrity guarantees, but fully trust the server for consistency. However, many applications consider strong consistency a security property: a Byzantine server can corrupt application state by manipulating operation orders. We present SCUBA, an end-to-end encrypted framework for strongly-consistent applications in a Byzantine setting. At its core, the SCUBA protocol establishes strong privacy, integrity, and ordering guarantees that let applications achieve up to the strongest single- and multi-key consistency models known to date. SCUBA upholds all consistency guarantees in the face of a Byzantine server, and lets clients prove a server misbehaved to a third party. We build four previously-unsupported applications on top of the SCUBA key-value store, and show that SCUBA imposes minimal overheads and can support many applications at once. SCUBA enables entire classes of applications to benefit from end-to-end encryption.