  Reliable on-off control of peripherals on smart devices is a key to security
and privacy in many scenarios. Journalists want to reliably turn off radios to
protect their sources during investigative reporting. Users wish to ensure
cameras and microphones are reliably off during private meetings. In this
paper, we present SeCloak, an ARM TrustZone-based solution that ensures
reliable on-off control of peripherals even when the platform software is
compromised. We design a secure kernel that co-exists with software running on
mobile devices (e.g., Android and Linux) without requiring any code
modifications. An Android prototype demonstrates that mobile peripherals like
radios, cameras, and microphones can be controlled reliably with a very small
trusted computing base and with minimal performance overhead.
