in-toto

in-toto is a framework and specification for cryptographically securing the integrity of a software supply chain. It defines a signed layout that declares every step a project must take from source to finished artifact, and it collects signed link metadata as each step actually runs — so a verifier can prove the software was built exactly as intended, by the expected parties, with nothing inserted or skipped along the way.

• Layouts - A signed policy describing the ordered steps of the supply chain and who is authorized to perform each one.
• Link metadata - Cryptographically signed records of what each step consumed and produced, tying materials to products.
• End-to-end verification - A final check confirms the delivered artifact matches an unbroken, authorized chain of steps.
• Attestation framework - in-toto attestations provide a common envelope that tools like SLSA and Sigstore build on.

in-toto has become foundational infrastructure for the software supply chain security movement, underpinning SLSA provenance and integrating with build systems, package registries, and CI/CD pipelines. As APIs are increasingly assembled from third-party dependencies and shipped through automated pipelines, in-toto is one of the mechanisms that lets a consumer — human or agent — trust that the artifact they are running is the one the producer actually built and signed.