Sigstore: Software Signing for Everybody

Abstract

Software supply chain compromises are on the rise. From the effects of XCodeGhost to SolarWinds, hackers have identified that targeting weak points in the supply chain allows them to compromise high-value targets such as U.S. government agencies and corporate targets such as Google and Microsoft. Software signing, a promising mitigation for many of these attacks, has seen limited adoption in open-source and enterprise ecosystems. In this paper, we propose Sigstore, a system to provide widespread software signing capabilities. To do so, we designed the system to provide baseline artifact signing capabilities that minimize the adoption barrier for developers. To this end, Sigstore leverages three distinct mechanisms: First, it uses a protocol similar to ACME to authenticate developers through OIDC, tying signatures to existing and widely-used identities. Second, it enables developers to use ephemeral keys to sign their artifacts, reducing the inconvenience and risk of key management. Finally, Sigstore enables user authentication by means of artifact and identity logs, bringing transparency to software signatures. Sigstore is quickly becoming a critical piece of Internet infrastructure with more than 2.2M signatures over critical software such as Kubernetes and Distroless.