  Personal voice assistants (VAs) are shown to be vulnerable against
record-and-replay, and other acoustic attacks which allow an adversary to gain
unauthorized control of connected devices within a smart home. Existing
defenses either lack detection and management capabilities or are too
coarse-grained to enable flexible policies on par with other computing
interfaces. In this work, we present Sesame, a lightweight framework for edge
devices which is the first to enable fine-grained access control of smart-home
voice commands. Sesame combines three components: Automatic Speech Recognition,
Natural Language Understanding (NLU) and a Policy module. We implemented Sesame
on Android devices and demonstrate that our system can enforce security
policies for both Alexa and Google Home in real-time (362ms end-to-end
inference time), with a lightweight (<25MB) NLU model which exhibits minimal
accuracy loss compared to its non-compact equivalent.
