Temporal Consistency of Integrity-Ensuring Computations and Applications to Embedded Systems Security

Abstract

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.