Hey Kimya, Is My Smart Speaker Spying on Me? Taking Control of Sensor Privacy Through Isolation and Amnesia

Although smart speakers and other voice assistants are becoming increasingly ubiquitous, their always-standby nature continues to prompt significant privacy concerns. To address these, we propose Kimya, a hardening framework that allows device vendors to provide strong data-privacy guarantees. Concretely, Kimya guarantees that microphone data can only be used for local processing, and is immediately discarded unless a user-auditable notification is generated. Kimya thus makes devices accountable for their data-retention behavior. Moreover, Kimya is not limited to voice assistants, but is applicable to all devices with always-standby, event-triggered sensors. We implement Kimya for ARM Cortex-M, and apply it to a wake-word detection engine. Our evaluation shows that Kimya introduces low overhead, can be used in constrained environments, and does not require hardware modifications.