SLSA protects against tampering during the software supply chain, but how? The answer depends on the use case in which SLSA is applied. Below describe the three main use cases for SLSA.
Applications of SLSA
Reducing risk within an organization from insiders and compromised accounts
In its simplest form, SLSA can be used entirely within an organization to reduce risk from internal sources. This is the easiest case in which to apply SLSA because there is no need to transfer trust across organizational boundaries.
Example ways an organization might use SLSA internally:
- A small company or team uses SLSA to ensure that the code being deployed to production in binary form is the same one that was tested and reviewed in source form.
- A large company uses SLSA to require two person review for every production change, scalably across hundreds or thousands of employees/teams.
- An open source project uses SLSA to ensure that compromised credentials cannot be abused to release an unofficial package to a package repostory.
Case study: Google (Binary Authorization for Borg)
Reducing risk from consuming open source software
SLSA can also be used to reduce risk for consumers of open source software. The focus here is to map built packages back to their canonical sources and dependencies. In this way, consumers need only trust a small number of secure build platforms rather than the many thousands of developers with upload permissions across various packages.
Example ways an open source ecosystem might use SLSA to protect users:
- At upload time, the package registry rejects the package if it was not built from the canonical source repository.
- At download time, the packaging client rejects the package if it was not built by a trusted builder.
Case study: SUSE
Reducing risk from consuming vendor provided software and services
Finally, SLSA can be used to reduce risk for consumers of vendor provided software and services. Unlike open source, there is no canonical source repository to map to, so instead the focus is on trustworthiness of claims made by the vendor.
Example ways a consumer might use SLSA for vendor provided software:
- Prefer vendors who make SLSA claims and back them up with credible evidence.
- Require a vendor to implement SLSA as part of a contract.
- Require a vendor to be SLSA certified from a trusted third-party auditor.
For a look at how SLSA might be applied to open source in the future, see the hypothetical curl example.