Remote attestation protocols are widely used to detect device configuration (e.g., software and/or data) compromise in Internet of Things (IoT) scenarios. Unfortunately, the performances of such protocols are unsatisfactory when dealing with thousands of smart devices. Recently, researchers are focusing on addressing this limitation. The approach is to run attestation in a collective way, with the goal of reducing computation and communication. Despite these advances, current solutions for attestation are still unsatisfactory because of their complex management and strict assumptions concerning the topology (e.g., being time invariant or maintaining a fixed topology). In this paper, we propose PADS, a secure, efficient, and practical protocol for attesting potentially large networks of smart devices with unstructured or dynamic topologies. PADS builds upon the recent concept of non-interactive attestation, by reducing the collective attestation problem into a minimum consensus one. We compare PADS with a state-of-the art collective attestation protocol and validate it by using realistic simulations that show practicality and efficiency. The results confirm the suitability of PADS for low-end devices, and highly unstructured networks. 5

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In recent years, the booming of Internet of Things (IoT) has populated the world with billions of smart devices that implement novel services and applications. The potential for cyberattacks on IoT systems have called for new solutions from the research community. Remote attestation is a widely used technique that allows a verifier to identify software compromise on a remote platform (called prover). Traditional challengeresponse remote attestation protocols between the verifier and a single prover face a severe scalability challenge when they are applied to large scale IoT systems. To tackle this issue, recently researchers have started developing attestation schemes, which we refer to as Collective Remote Attestation (CRA) schemes, that are capable of remotely performing attestation of large networks of IoT devices.In this paper, after providing the reader with a background on remote attestation, we survey and analyze existing CRA schemes. We present an analysis of their advantages and disadvantages, as well as of their effectiveness against a reference attacker model. We focus our attention on CRA schemes' characteristics and adversarial mitigation capabilities. We finally highlight open research issues and give possible directions for mitigating both the limitations of existing schemes, and new emerging challenges. We believe this work can help guiding the design of current and future proposals for CRA.

This paper proposes a novel mechanism for swarm attestation, i.e., the remote attestation of a multitude of interconnected devices, also called a swarm of devices. Classical remote attestation protocols work with one prover and one verifier. Swarm attestation protocols assume that the devices in the swarm act both as verifier and prover in order to attest the software integrity of all the devices to a root verifier, typically in a spanning-tree topology. We propose "SHeLA: Scalable Heterogeneous Layered Attestation", a novel remote attestation technique for swarms. Our approach consists of introducing an additional edge layer in between the root verifier and the swarm devices. The edge layer consists of geographically spread devices with a larger computational power and storage capacity than the swarm devices. The main challenges we address are related to the scalability of the swarm, the availability or visibility of the nodes (especially when they are mobile), the heterogeneity of the devices with respect to the wireless communication protocol and interface, and the granularity of the attestation in terms of detecting the sanity of individual swarm devices. We build a proof-of-concept network that allows us to evaluate the computational delay and the resource overhead of the edge and swarm devices, and to perform a thorough security analysis.