Interaction-Based Privacy Threat Elicitation

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Abstract
Threat modeling involves the systematic identification, elicitation, and analysis of privacy- and/or security-related threats in the context of a specific system. These modeling practices are performed at a specific level of architectural abstraction - the use of Data Flow Diagram (DFD) models, for example, is common in this context. To identify and elicit threats, two fundamentally different approaches can be taken: (1) elicitation on a per-element basis involves iteratively singling out individual architectural elements and considering the applicable threats, (2) elicitation at the level of system interactions (which involve the local context of three elements: a source, a data flow, and a destination) performs elicitation at the basis of system-level communication. Although not considering the local context of the element under investigation makes the former approach easier to adopt and use for human analysts, this approach also leads to threat duplication and redundancy, relies more extensively on implicit analyst expertise, and requires more manual effort. In this paper, we provide a detailed analysis of these issues with element-based threat elicitation in the context of LINDDUN, an element-driven privacy-by-design threat modeling methodology. Subsequently, we present a LINDDUN extension that implements interaction-based privacy threat elicitation and we provide indepth argumentation on how this approach leads to better process guidance and more concrete interpretation of privacy threat types, ultimately requiring less effort and expertise. A third standalone contribution of this work is a catalog of realistic and illustrative LINDDUN privacy threats, which in turn facilitates practical threat elicitation using LINDDUN.