  Contemporary IoT environments, such as smart buildings, require end-users to
trust data-capturing rules published by the systems. There are several reasons
why such a trust is misplaced -- IoT systems may violate the rules deliberately
or IoT devices may transfer user data to a malicious third-party due to
cyberattacks, leading to the loss of individuals' privacy or service integrity.
To address such concerns, we propose IoT Notary, a framework to ensure trust in
IoT systems and applications. IoT Notary provides secure log sealing on live
sensor data to produce a verifiable `proof-of-integrity,' based on which a
verifier can attest that captured sensor data adheres to the published
data-capturing rules. IoT Notary is an integral part of TIPPERS, a smart space
system that has been deployed at the University of California Irvine to provide
various real-time location-based services on the campus. We present extensive
experiments over realtime WiFi connectivity data to evaluate IoT Notary, and
the results show that IoT Notary imposes nominal overheads. The secure logs
only take 21% more storage, while users can verify their one day's data in less
than two seconds even using a resource-limited device.
