  Remote attestation is a crucial security service particularly relevant to
increasingly popular IoT (and other embedded) devices. It allows a trusted
party (verifier) to learn the state of a remote, and potentially
malware-infected, device (prover). Most existing approaches are static in
nature and only check whether benign software is initially loaded on the
prover. However, they are vulnerable to run-time attacks that hijack the
application's control or data flow, e.g., via return-oriented programming or
data-oriented exploits. As a concrete step towards more comprehensive run-time
remote attestation, we present the design and implementation of Control- FLow
ATtestation (C-FLAT) that enables remote attestation of an application's
control-flow path, without requiring the source code. We describe a full
prototype implementation of C-FLAT on Raspberry Pi using its ARM TrustZone
hardware security extensions. We evaluate C-FLAT's performance using a
real-world embedded (cyber-physical) application, and demonstrate its efficacy
against control-flow hijacking attacks.
