It’s like flossing your teeth: On the Importance and Challenges of Reproducible Builds for Software Supply Chain Security

The 2020 Solarwinds attack was a tipping point that caused a heightened awareness about the security of the software supply chain and in particular the large amount of trust placed in build systems. Reproducible Builds (R-Bs) provide a strong foundation to build defenses for arbitrary attacks against build systems by ensuring that given the same source code, build environment, and build instructions, bitwise-identical artifacts are created. Unfortunately, much of the software industry believes R-Bs are too far out of reach for most projects. The goal of this paper is to help identify a path for R-Bs to become a commonplace property.To this end, we conducted a series of 24 semi-structured expert interviews with participants from the Reproducible-Builds.org project, finding that self-effective work by highly motivated developers and collaborative communication with upstream projects are key contributors to R-Bs. We identified a range of motivations that can encourage open source developers to strive for R-Bs, including indicators of quality, security benefits, and more efficient caching of artifacts. We also identify experiences that help and hinder adoption, which often revolves around communication with upstream projects. We conclude with recommendations on how to better integrate R-Bs with the efforts of the open source and free software community.