Biblio

Remote Attestation ( RA) is a security service that enables a trusted verifier ( Vrf) to measure current memory state of an untrusted remote prover ( Prv). If correctly implemented, RA allows Vrf to remotely detect if Prv's memory reflects a compromised state. However, RA by itself offers no means of remedying the situation once P rv is determined to be compromised. In this work we show how a secure RA architecture can be extended to enable important and useful security services for low-end embedded devices. In particular, we extend the formally verified RA architecture, VRASED, to implement provably secure software update, erasure, and system-wide resets. When (serially) composed, these features guarantee to Vrf that a remote Prv has been updated to a functional and malware-free state, and was properly initialized after such process. These services are provably secure against an adversary (represented by malware) that compromises Prv and exerts full control of its software state. Our results demonstrate that such services incur minimal additional overhead (0.4% extra hardware footprint, and 100-s milliseconds to generate combined proofs of update, erasure, and reset), making them practical even for the lowest-end embedded devices, e.g., those based on MSP430 or AVR ATMega micro-controller units (MCUs). All changes introduced by our new services to VRASED trusted components are also formally verified.

Networks of and embedded (IoT) devices are becoming increasingly popular, particularly, in settings such as smart homes, factories and vehicles. These networks can include numerous (potentially diverse) devices that collectively perform certain tasks. In order to guarantee overall safety and privacy, especially in the face of remote exploits, software integrity of each device must be continuously assured. This can be achieved by Remote Attestation (RA) - a security service for reporting current software state of a remote and untrusted device. While RA of a single device is well understood, collective RA of large numbers of networked embedded devices poses new research challenges. In particular, unlike single-device RA, collective RA has not benefited from any systematic treatment. Thus, unsurprisingly, prior collective RA schemes are designed in an ad hoc fashion. Our work takes the first step toward systematic design of collective RA, in order to help place collective RA onto a solid ground and serve as a set of design guidelines for both researchers and practitioners. We explore the design space for collective RA and show how the notions of security and effectiveness can be formally defined according to a given application domain. We then present and evaluate a concrete collective RA scheme systematically designed to satisfy these goals.

Assuring integrity of information (e.g., data and/or software) is usually accomplished by cryptographic means, such as hash functions or message authentication codes (MACs). Computing such integrity-ensuring functions can be time-consuming if the amount of input data is large and/or the computing platform is weak. At the same time, in real-time or safety-critical settings, it is often impractical or even undesirable to guarantee atomicity of computing a time-consuming integrity-ensuring function. Meanwhile, standard correctness and security definitions of such functions assume that input data (regardless of its size) remains consistent throughout computation. However, temporal consistency may be lost if another process interrupts execution of an integrity-ensuring function and modifies portions of input that either or both: (1) were already processed, or (2) were not processed yet. Lack of temporal consistency might yield an integrity result that is non-sensical or simply incorrect. Such subtleties and discrepancies between (implicit) assumptions in definitions and implementations can be a source of inconsistenceies, which might lead to vulnerabilities. In this paper, we systematically explore the notion of temporal consistency of cryptographic integrity-ensuring functions. We show that its lack in implementations of such functions can lead to inconsistent results and security violations in protocols and systems using them, e.g., remote attestation, remote updates and secure resets. We consider several mechanisms that guarantee temporal consistency of implementations of integrity-ensuring functions in embedded systems with a focus on remote attestation. We also assess performance of proposed mechanisms on two commodity hardware platforms: I.MX6-SabreLite and ODROID-XU4.