Secure Application Continuity in Intermittent Systems

Abstract

Intermittent systems operate embedded devices without a source of constant reliable power, relying instead on an unreliable source such as an energy harvester. They overcome the limitation of intermittent power by retaining and restoring system state as checkpoints across periods of power loss. Previous works have addressed a multitude of problems created by the intermittent paradigm, but do not consider securing intermittent systems. In this paper, we address the security concerns created through the introduction of checkpoints to an embedded device. When the non-volatile memory that holds checkpoints can be tampered, the checkpoints can be replayed or duplicated. We propose secure application continuity as a defense against these attacks. Secure application continuity provides assurance that an application continues where it left off upon power loss. In our secure continuity solution, we define a protocol that adds integrity, authenticity, and freshness to checkpoints. We develop two solutions for our secure checkpointing design. The first solution uses a hardware accelerated implementation of AES, while the second one is based on a software implementation of a lightweight cryptographic algorithm, Chaskey. We analyze the feasibility and overhead of these designs in terms of energy consumption, execution time, and code size across several application configurations. Then, we compare this overhead to a non-secure checkpointing system. We conclude that securing application continuity does not come cheap and that it increases the overhead of checkpoint restoration from 3.79 μJ to 42.96 μJ with the hardware accelerated solution and 57.02 μJ with the software based solution. To our knowledge, no one has yet considered the cost to provide security guarantees for intermittent operations. Our work provides future developers with an empirical evaluation of this cost, and with a problem statement for future research in this area.