SobTrA: a software-based trust anchor for ARM cortex application processors

In this paper, we present SobTrA, a Software-based Trust Anchor for ARM Cortex-A processors to protect systems against software-based attacks. SobTrA enables the implementation of a software-based secure boot controlled by a third party independent from the manufacturer. Compared to hardware-based trust anchors, our concept provides some other advantages like being updateable and also usable on legacy hardware. The presented software-based trust anchor involves a trusted third party device, the verifier, locally connected to the untrusted device, e.g., via the microSD card slot of a smartphone. The verifier is verifying the integrity of the untrusted device by making sure that a piece of code is executed untampered on it using a timing-based approach. This code can then act as an anchor for a chain of trust similar to a hardware-based secure boot. Tests on our prototype showed that tampered and untampered execution of SobTrA can be clearly and reliably distinguished.