Boosting Device Utilization in Control Flow Auditing
2026-03-02 • Cryptography and Security
Cryptography and Security
AI summaryⓘ
The authors focus on improving security for small microcontrollers used in important systems by making sure their control flow can be audited remotely, even if their software is hacked. Existing methods require the device to pause and wait during this audit, wasting processing time. The authors developed CARAMEL, a combined hardware and software design that lets the device keep working while sending audit information, improving efficiency without losing security. They implemented and tested CARAMEL, showing it uses the CPU better with only a small increase in hardware needed.
Microcontroller UnitsControl Flow AuditingRoot of TrustHardware-Software Co-designCPU UtilizationSecurityRemote VerificationBusy-waitEmbedded Systems
Authors
Alexandra Lengert, Adam Ilyas Caulfield, Ivan De Oliveira Nunes
Abstract
Micro-Controller Units (MCUs) are widely used in safety-critical systems, making them attractive targets for attacks. This calls for lightweight defenses that remain effective despite software compromise. Control Flow Auditing (CFAud) is one such mechanism wherein a remote verifier (Vrf) is guaranteed to received evidence about the control flow path taken on a prover (Prv) MCU, even when Prv software is compromised. Despite promising benefits, current CFAud architectures unfortunately require a ``busy-wait'' phase where a hardware-anchored root-of-trust (RoT) in Prv retains execution control to ensure delivery of control flow evidence to Vrf. This drastically reduces the CPU utilization on Prv. In this work, we addresses this limitation with an architecture for Contention Avoidance in Runtime Auditing with Minimized Execution Latency (CARAMEL). CARAMEL is a hardware-software RoT co-design that enables Prv applications to resume while control flow evidence is transmitted to Vrf. This significantly reduces contention due to transmission delays and improves CPU utilization without giving up on security. Key to CARAMEL is our design of a new RoT with a self-contained (and minimal) dedicated communication interface. CARAMEL's implementation and accompanying evaluation are made open-source. Our results show substantially improved CPU utilization at a modest hardware cost.