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  1. null (Ed.)
  2. Intermittent computing systems execute long-running tasks under a transient power supply such as an energy harvesting power source. During a power loss, they save intermediate program state as a checkpoint into write-efficient non-volatile memory. When the power is restored, the system state is reconstructed from the checkpoint, and the long-running computation continues. We analyze the security risks when power interruption is used as an attack vector, and we demonstrate the need to protect the integrity, authenticity, confidentiality, continuity, and freshness of checkpointed data. We propose a secure checkpointing technique called the Se-cure Intermittent Computing Protocol (SICP). The proposed protocol has the following properties. First, it associates every checkpoint with a unique power-on state to checkpoint replay. Second, every checkpoint is cryptographically chained to its predecessor, providing continuity, which enables the programmer to carry run-time security properties such as attested program images across power loss events. Third, SICP is atomic and resistant to power loss. We demonstrate a prototype implementation of SICP on an MSP430 microcontroller, and we investigate the overhead of SICP for several cryptographic kernels. To the best of our knowledge, this is the first work to provide a robust solution to secure intermittent computing. 
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  3. 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. 
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  4. The Internet of Things will need to support ubiquitous and continuous connectivity to resource constrained and energy constrained devices. To this end, we consider the optimization of cryptographic protocols under energy harvesting conditions. Traditionally, computing using energy harvesting power sources is handled as a case of intermittent-computing: working towards the completion of a goal under uncertain energy supply. In our work we consider the often ignored case when there is harvested energy available but there are no useful operations to complete. In cryptographic protocols, this can occur while the protocol waits for the next message. To avoid waste, we partition cryptographic algorithms into an offline portion and an online portion, where only the online portion has a real-time dependency to the availability of data. The offline portion is precomputed with the result stored as a coupon for the remaining online operation. We show that this structure brings multiple benefits including decreased response latency, a smaller energy store requirement, and reduced energy waste in a harvester supported system. We present a case study of two canonical cryptographic applications: true random number generation and bulk-encryption. We analyze the precomputed implementations on an MSP430 with ferroelectric RAM and an ARM Cortex M4 with nonvolatile flash memory. Our solutions avoid energy waste during the offline phase, and they offer gains in energy efficiency during the online phase of up to 57 times for bulk-encryption and over 100 times for random number generation. 
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