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  1. null (Ed.)
  2. Intermittent computing applications in the IoT space, such as long-term monitoring of the structural integrity of infrastructures, rely on battery-less computing systems powered through scavenged energy. For such systems, power-loss is a fact of life, and there is a need for a secure power transition mechanism to convert the active system state into a protected nonvolatile form and back. We evaluate the architectural needs to secure these power transitions and to adapt computations based on the scavenged energy. Our objective is to enforce confidentiality, integrity, freshness, and authenticity over the system state across power loss. We observe that secure power transitions are delicate and complex. We need secure checkpoints which are expensive to compute, and which may require hardware-accelerated cryptography and isolated secure non-volatile storage. Next, we observe that in intermittent systems, the energy subsystem does not adapt to the needs of the application. Rather, the application must adjust its computing pattern to the available energy. We define an energy-harvester subsystem interface to optimize the run-time activity of the intermittent system. The interface drives the optimized execution of a secure communication protocol (covering key-exchange and bulk encryption), such that wasted energy is eliminated and that run-time performance is improved. We report results from several prototyping experiments. 
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  3. Recent advancements in energy-harvesting techniques provide an alternative to batteries for resource constrained IoT devices and lead to a new computing paradigm, the intermittent computing model. In this model, a software module continues its execution from where it left off when an energy shortage occurred. Enforcing security of an intermittent software module is challenging because its power-off state has to be protected from a malicious adversary in addition to its power-on state, while the security mechanisms put in place must have a low overhead on the performance, resource consumption, and cost of a device. In this paper, we propose SIA (Secure Intermittent Architecture), a security architecture for resource-constrained IoT devices. SIA leverages low-cost security features available in commercial off-the-shelf microcontrollers to protect both the power-on and power-off state of an intermittent software module. Therefore, SIA enables a host of secure intermittent computing applications such as self-attestation, remote attestation, and secure communication. Moreover, our architecture provides confidentiality and integrity guarantees to an intermittent computing module at no cost compared to previous approaches in the literature that impose significant overheads. The salient characteristic of SIA is that it does not require any hardware modifications, and hence, it can be directly applied to existing IoT devices. We implemented and evaluated SIA on a resource-constrained IoT device based on an MSP430 processor. Besides being secure, SIA is simple and efficient. We confirm the feasibility of SIA for resource-constrained IoT devices with experimental results of several intermittent computing applications. Our prototype implementation outperforms by two to three orders of magnitude the secure intermittent computing solution of Suslowicz et al. presented at IGSC 2018. 
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  4. Energy harvesters have enabled widespread utilization of ultra-low-power devices that operate solely based on the energy harvested from the environment. Due to the unpredictable nature of harvested energy, these devices experience frequent power outages. They resume execution after a power loss by utilizing intermittent computing techniques and non-volatile memory. In embedded devices, intermittent computing refers to a class of computing that stores a snapshot of the system and application state, as a checkpoint, in non-volatile memory, which is used to restore the system and application state in case of power loss. Although non-volatile memory provides tolerance against power failures, they introduce new vulnerabilities to the data stored in them. Sensitive data, stored in a checkpoint, is available to an attacker after a power loss, and the state-of-the-art intermittent computing techniques fail to consider the security of checkpoints. In this paper, we utilize the vulnerabilities introduced by the intermittent computing techniques to enable various implementation attacks. For this study, we focus on TI’s Compute Through Power Loss utility as an example of the state-of-the-art intermittent computing solution. First, we analyze the security, or lack thereof, of checkpoints in the latest intermittent computing techniques. Then, we attack the checkpoints and locate sensitive data in non-volatile memory. Finally, we attack AES using this information to extract the secret key. To the best of our knowledge, this work presents the first systematic analysis of the seriousness of security threats present in the field of intermittent computing. 
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  5. 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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  6. 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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  7. 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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