Although it’s tempting to attempt to set up a single commonplace for the way to use SLSA, it’s not attainable: SLSA is just not a line dance the place everybody does the identical strikes, on the similar time, to the identical track. It’s a diverse system with completely different types, strikes, and thrives. The open supply neighborhood, organizations, and shoppers could all implement SLSA in a different way, however they will nonetheless work with one another.
On this three-part collection, we’ll discover how three fictional organizations would apply SLSA to fulfill their completely different wants. In doing so, we are going to reply among the fundamental questions that newcomers to SLSA have:
Half 1: The fundamentals
- How and when do you confirm a package deal with SLSA?
- Methods to deal with artifacts with out provenance?
Half 2: The small print
- The place is the provenance saved?
- The place is the suitable coverage saved and who ought to confirm it?
- What ought to the insurance policies examine?
- How do you determine belief & distribute keys?
Half 3: Placing all of it collectively
- What does a safe, heterogeneous provide chain appear to be?
Our fictional instance entails three organizations that wish to use SLSA:
Squirrel: a package deal supervisor with a lot of builders and customers
Oppy: an open supply working system with an enterprise distribution
Acme: a mid sized enterprise.
Squirrel needs to make SLSA as straightforward for his or her customers as attainable, even when meaning abstracting some particulars away. In the meantime, Oppy doesn’t wish to summary something away from their customers underneath the philosophy that they need to explicitly perceive precisely what they’re consuming.
Acme is making an attempt to supply a container picture that comprises three artifacts:
- The Squirrel package deal ‘foo’
- The Oppy package deal ‘baz’
- A customized executable, ‘bar’, written by Acme staff
This collection demonstrates one strategy to utilizing SLSA that lets Acme confirm the Squirrel and Oppy packages ‘foo’ and ‘baz’ and its prospects confirm the container picture. Although not each instructed answer is ideal, the options described generally is a start line for dialogue and a basis for brand spanking new options.
Squirrel, Oppy, and Acme will comply with an analogous qualification course of for the supply management programs they plan to help.
Sooner or later, a number of of the organizations might want to do full verification of every artifact to find out whether it is acceptable for a given use case. That is achieved by checking if the artifact meets the suitable coverage.
Usually, full verification would happen with, , and maybe different specialised attestations (like ). Whereas having to coordinate this knowledge for all of its dependencies looks like numerous work to Acme, they’re ready to do full verification if Squirrel and Oppy are unable to.
When Acme isn’t utilizing full verification, they will as an alternative use delegated verification the place they examine if an artifact is suitable for a use case by checking if another trusted occasion who carried out a full verification (similar to Squirrel or Oppy) believes the artifact is suitable.
Delegated verification is less complicated to carry out rapidly with restricted knowledge and community connectivity. It could even be simpler for some customers who worth if somebody they belief verified the artifact is nice.
Squirrel likes how straightforward delegated verification would make issues for his or her customers and plans to help it by making aafter they carry out full verification.
Verification (full or delegated) may occur at quite a lot of completely different occasions.
Squirrel plans to carry out full verification when an artifact is printed to their repo. This can be sure that packages within the repo have met their corresponding coverage. It’s additionally useful as a result of all of the required knowledge will be gathered when latency isn’t crucial.
If this had been the one time verification is carried out, it might put the repository’s storage within the trusted computing base (TCB) of its customers. Squirrel’s plans to make use of delegated verification (and subject VSAs) can forestall this. The signature on the VSA will forestall the artifacts from being tampered with whereas sitting in storage, even when they’re simply SLSA 0. Downstream customers will simply have to confirm the VSA.
Acme additionally needs to do some type of verification on the import to their inside repo because it simplifies their safety story. They’re not fairly positive what this may appear to be but.
Acme additionally needs to do verification when an artifact is definitely put in since it will possibly take away quite a lot of intermediaries from their TCB (their repo, the community, upstream storage programs).
In the event that they carry out full verification at set up then they have to collect all of the required info. That may very well be numerous knowledge, nevertheless it could be simplified by gathering the info from exterior sources and caching it of their inside repo. A bigger downside is that it requires Acme to have established belief in all events that produced that info (e.g. each builder of each package deal). For a posh provide chain that could be troublesome.
If Acme performs delegated verification, they solely want the VSA for the packages being put in and to explicitly belief a handful of events. This permits the advanced full verification to be carried out as soon as whereas permitting all customers of that package deal to carry out a a lot less complicated operation.
Given these tradeoffs Acme prefers delegated verification at set up time. Squirrel additionally actually likes the thought and plans to construct set up time verification immediately into the Squirrel device.
Time of use verification permits essentially the most context with which choices will be made (“is that this job allowed to run this code and is it free from vulns proper now?”). It additionally permits coverage modifications to have an effect on already constructed & put in software program (which can or will not be fascinating).
Acme needs their customers to have the ability to confirm on use with out too many dependencies in order that they plan to supply VSAs customers can use to carry out delegated verification after they begin the container (maybe utilizing one thing like).
Such an artifact would probably not be accepted at larger SLSA ranges, however the provenance can be utilized to: 1) forestall tampering with the artifact after it’s been imported and a pair of) be a knowledge level for future evaluation (e.g. ought to we prioritize asking for foo.tgz to be distributed with native SLSA provenance?).
Acme could be curious about taking this strategy sooner or later, however they don’t want it for the time being.
In our subsequent put up we’ll cowl particular approaches that can be utilized to reply questions like “the place ought to attestations and insurance policies be saved?” and “how do I belief the attestations that I obtain?”