Tracks
SLSA is composed of multiple tracks which are each composed of multiple levels. Each track addresses different threats and has its own set of requirements and patterns of use.
Build Track
The SLSA build track describes increasing levels of trustworthiness and completeness in a package artifact’s provenance. Provenance describes what entity built the artifact, what process they used, and what the inputs were. The lowest level only requires the provenance to exist, while higher levels provide increasing protection against tampering of the build, the provenance, or the artifact.
The primary purpose of the build track is to enable verification that the artifact was built as expected. Consumers have some way of knowing what the expected provenance should look like for a given package and then compare each package artifact’s actual provenance to those expectations. Doing so prevents several classes of supply chain threats.
Each ecosystem (for open source) or organization (for closed source) defines exactly how this is implemented, including: means of defining expectations, what provenance format is accepted, whether reproducible builds are used, how provenance is distributed, when verification happens, and what happens on failure. Guidelines for implementers can be found in the requirements.
Source Track
The SLSA source track provides producers and consumers with increasing levels of trust in the source code they produce and consume. It describes increasing levels of trustworthiness and completeness of how a source revision was created.
The expected process for creating a new revision is determined solely by that repository’s owner (the organization) who also determines the intent of the software in the repository and administers technical controls to enforce the process.
Consumers can review attestations to verify whether a particular revision meets their standards.
Build Environment track
The goal of a Build Environment track is to enable the detection of tampering with core components of the compute environment executing builds. The track describes increasing levels of integrity for different components of the build platform and its underlying compute platform.
At a general level, implementers of this track will generate SLSA Build Provenance for build images, validate the integrity of a build’s environment at boot time against good known values, and at L3 deploy the build system on compute that supports system state measurement and attestation capabilities at the hardware level.
Dependency Track
The SLSA Dependency Track defines requirements for the ingestion of
third-party build dependencies. It defines a per-ingestion attestation,
Dependency Ingestion Provenance, emitted by a Dependency Ingestion
Platform. Three levels grade the platform’s claims about each ingested
dependency: L1 Inventoried (identity recorded; other verdicts MAY be
recorded as transparency), L2 Controlled (configured ingestion path
including transitive deps; identity-verification verdicts MUST be
verified; admission policies the platform applies are recorded in
the Provenance; the platform signs the Provenance), and L3 Screened
(bypass structurally blocked; upstream-provenance verdict recorded;
signing infrastructure isolated from dep code and cross-dep ingestion
isolated, so a hostile dep cannot subvert the Provenance about itself
or about other deps — the Shai Hulud threat model).
The track imports the attestable subset of the OpenSSF Secure Supply Chain Consumption Framework (S2C2F). S2C2F requirements that describe organizational practice rather than per-artifact evidence are referred to the OpenSSF Security Baseline. S2C2F requirements that describe the ingestor producing their own producer-side Build attestations over consumed dependencies (via rebuild) are deferred to a future cross-cutting axis. See the S2C2F mapping appendix.
The track is for any organization that ingests third-party software dependencies. This includes software producers consuming upstream OSS and pure consumers such as enterprises that consume OSS internally without releasing downstream artifacts.