What is Software Supply Chain Security?

The software supply chain involves a multitude of tools and processes that enable software developers to write, build, and ship applications. Recently, security compromises of tools or processes has led to a surge in proposals to address these issues. However, these proposals commonly overemphasize specific solutions or conflate goals, resulting in unexpected consequences, or unclear positioning and usage. In this paper, we make the case that developing practical solutions is not possible until the community has a holistic view of the security problem; this view must include both the technical and procedural aspects. To this end, we examine three use cases to identify common security goals, and present a goal-oriented taxonomy of existing solutions demonstrating a holistic overview of software supply chain security.