Following the 2020 SolarWinds cyberespionage campaign, in which Russian hackers slipped tainted updates into a widely used IT management platform, a series of further software supply chain attacks continues to highlight the urgent need to lock down software chains of custody. And the issue is particularly pressing in open source, where projects are inherently decentralized and often ad hoc endeavors. After a series of worrying compromises to widely downloaded JavaScript software packages from the prominent “npm” registry, which is owned by GitHub, the company laid out a plan this week to offer expanded defenses for open source security.

GitHub, which itself is owned by Microsoft, announced on Monday that it plans to support code signing, a sort of digital wax seal, for npm software packages using the code-signing platform Sigstore. The tool grew out of cross-industry collaboration to make it much easier for open source maintainers to verify that the code they create is the same code that ends up in the software packages actually being downloaded by people worldwide.

“While most npm packages are open source, there’s currently no guarantee that a package on npm is built from the same source code that’s published,” says Justin Hutchings, GitHub’s director of product management. “Supply chain attacks are on the rise, and adding signed build information to open source packages that validates where the software came from and how it was built is a great way to reduce the attack surface.”

In other words, it’s all about creating a cryptographically verified and transparent game of telephone. 

Dan Lorenc, CEO of Chainguard, which co-develops Sigstore, emphasizes that while GitHub isn’t the only component of the open source ecosystem, it’s an absolutely crucial town square for the community because it’s where the vast majority of projects store and publish their source code. When developers actually want to download open source applications or tools, though, they typically go to a package manager 

“You don’t install source code directly, you usually install some compiled form of it, so something has happened in between the source code and the creation of the package. And up until now, that whole step has just been a black box in open source,” Lorenc explains. “You see the code and then go and download the package, but there’s nothing that proves that the package came from that code or the same person was involved, so that’s what GitHub is fixing.”

By offering Sigstore to package managers, there’s much more transparency at every stage of the software’s journey, and the Sigstore tools help developers manage cryptographic checks and requirements as software moves through the supply chain. Lorenc says that many people are shocked to hear that these integrity checks aren’t already in place and that so much of the open source ecosystem has been relying on blind trust for so long. In May 2021, the Biden White House issued an executive order that specifically addressed software supply chain security.