  We propose Remote Attestation with TOCTOU Avoidance (RATA): a provably secure
approach to address the RA TOCTOU problem. With RATA, even malware that erases
itself before execution of the next RA, can not hide its ephemeral presence.
RATA targets hybrid RA architectures (implemented as Hardware/Software
co-designs), which are aimed at low-end embedded devices. We present two
alternative techniques - RATAa and RATAb - suitable for devices with and
without real-time clocks, respectively. Each is shown to be secure and
accompanied by a publicly available and formally verified implementation. Our
evaluation demonstrates low hardware overhead of both techniques. Compared with
current RA architectures - that offer no TOCTOU protection - RATA incurs no
extra runtime overhead. In fact, RATA substantially reduces computational costs
of RA execution.

Cryptography and Security