Delegated attestation: scalable remote attestation of commodity CPS by blending proofs of execution with software attestation

Remote Attestation (RA) is an interaction between a trusted verifier (Vrf) and one or more remote and potentially compromised devices (provers or Prv-s) that allow the former to measure the software state of the latter. RA is particularly relevant to safety-critical cyber-physical systems (CPS) where a set of low-end micro-controllers (MCUs), operate under the control of a remote and more powerful controller. In such cases, RA is an effective and relatively efficient means to detect software compromise, e.g., malware infections, on these low-end MCUs that cannot support expensive security mechanisms.

Unfortunately, current RA techniques have a major practical limitation by requiring one or more of: (i) customized hardware support on every Prv; or (ii) physical presence of Vrf, which must be directly connected to all Prv-s, or (iii) secure pre-loading of trusted software. To overcome this limitation, we construct, implement and evaluate a Delegated Attestation (DA) scheme. In it, all Prv-s remain unmodified, meaning that it applies even to already deployed CPS devices. However, there is no requirement for Vrf's physical proximity, hardware support or secure initial software pre-loading. Instead, DA uses a recently proposed primitive (called Proofs-of-Execution or PoX) which entails a single customized low-end embedded device (called Attestation Proxy or Prox) on the same local-area network (e.g., a CAN-bus) as Prv-s. In doing so, DA enables RA of all Prv-s. Importantly, this guarantee holds even if Prox is itself compromised, enabling secure RA of completely unmodified Prv-s in an efficient manner.