From e60b44281ee80cc3bd98bb9a4894d03e7da6e268 Mon Sep 17 00:00:00 2001 From: Mark Lodato Date: Fri, 18 Aug 2023 08:09:31 -0400 Subject: [PATCH] content: create v1.1 directory (#942) The spec/v1.1/ directory is a copy of spec/v1.0/, while _data/nav/v1.1.yml is a copy of v1.0.yml with "1.0" replaced by "1.1". ```bash $ git ls-tree HEAD:docs/spec | grep 'v1.[01]$' 040000 tree 52008aa2d63ee43de55af463c016ea2b6771433a v1.0 040000 tree 52008aa2d63ee43de55af463c016ea2b6771433a v1.1 ``` Signed-off-by: Mark Lodato --- docs/_data/nav/config.yml | 1 + docs/_data/nav/v1.1.yml | 125 ++++ docs/_data/versions.yml | 5 + docs/_redirects | 2 + docs/spec/v1.1/about.md | 142 +++++ docs/spec/v1.1/distributing-provenance.md | 170 +++++ docs/spec/v1.1/faq.md | 156 +++++ docs/spec/v1.1/future-directions.md | 77 +++ docs/spec/v1.1/images/build-model.svg | 1 + docs/spec/v1.1/images/provenance-model.svg | 1 + docs/spec/v1.1/images/supply-chain-model.svg | 28 + ...upply-chain-threats-build-verification.svg | 84 +++ .../spec/v1.1/images/supply-chain-threats.svg | 77 +++ docs/spec/v1.1/images/verification-model.svg | 1 + docs/spec/v1.1/index.md | 27 + docs/spec/v1.1/levels.md | 235 +++++++ docs/spec/v1.1/onepage.md | 13 + docs/spec/v1.1/principles.md | 82 +++ docs/spec/v1.1/provenance.md | 586 ++++++++++++++++++ docs/spec/v1.1/requirements.md | 338 ++++++++++ docs/spec/v1.1/schema/provenance.cue | 46 ++ docs/spec/v1.1/schema/provenance.proto | 50 ++ docs/spec/v1.1/terminology.md | 339 ++++++++++ docs/spec/v1.1/threats-overview.md | 110 ++++ docs/spec/v1.1/threats.md | 524 ++++++++++++++++ docs/spec/v1.1/use-cases.md | 129 ++++ docs/spec/v1.1/verification_summary.md | 291 +++++++++ docs/spec/v1.1/verifying-artifacts.md | 301 +++++++++ docs/spec/v1.1/verifying-systems.md | 238 +++++++ docs/spec/v1.1/whats-new.md | 202 ++++++ 30 files changed, 4381 insertions(+) create mode 100644 docs/_data/nav/v1.1.yml create mode 100644 docs/spec/v1.1/about.md create mode 100644 docs/spec/v1.1/distributing-provenance.md create mode 100644 docs/spec/v1.1/faq.md create mode 100644 docs/spec/v1.1/future-directions.md create mode 100644 docs/spec/v1.1/images/build-model.svg create mode 100644 docs/spec/v1.1/images/provenance-model.svg create mode 100644 docs/spec/v1.1/images/supply-chain-model.svg create mode 100644 docs/spec/v1.1/images/supply-chain-threats-build-verification.svg create mode 100644 docs/spec/v1.1/images/supply-chain-threats.svg create mode 100644 docs/spec/v1.1/images/verification-model.svg create mode 100644 docs/spec/v1.1/index.md create mode 100644 docs/spec/v1.1/levels.md create mode 100644 docs/spec/v1.1/onepage.md create mode 100644 docs/spec/v1.1/principles.md create mode 100644 docs/spec/v1.1/provenance.md create mode 100644 docs/spec/v1.1/requirements.md create mode 100644 docs/spec/v1.1/schema/provenance.cue create mode 100644 docs/spec/v1.1/schema/provenance.proto create mode 100644 docs/spec/v1.1/terminology.md create mode 100644 docs/spec/v1.1/threats-overview.md create mode 100644 docs/spec/v1.1/threats.md create mode 100644 docs/spec/v1.1/use-cases.md create mode 100644 docs/spec/v1.1/verification_summary.md create mode 100644 docs/spec/v1.1/verifying-artifacts.md create mode 100644 docs/spec/v1.1/verifying-systems.md create mode 100644 docs/spec/v1.1/whats-new.md diff --git a/docs/_data/nav/config.yml b/docs/_data/nav/config.yml index 1428764f5..639cc6c03 100644 --- a/docs/_data/nav/config.yml +++ b/docs/_data/nav/config.yml @@ -8,6 +8,7 @@ url_to_key: v1: v10 v1-rc1: v10-rc1 v1-rc2: v10-rc2 + v1.1: v11 latest: v10 # TODO: when viewing spec v0.1, it would be better to link to attestations v0.2. diff --git a/docs/_data/nav/v1.1.yml b/docs/_data/nav/v1.1.yml new file mode 100644 index 000000000..bc5fad586 --- /dev/null +++ b/docs/_data/nav/v1.1.yml @@ -0,0 +1,125 @@ +# Pages that show in the nav aside and in the spec index page. +# The spec index does not show top-level elements without children. + +- title: Overview + url: /spec/v1.1/ + +- title: Understanding SLSA + description: > + These pages provide an overview of SLSA, how it helps protect against common + supply chain attacks, and common use cases. If you're new to SLSA or + supply chain security, start here. + children: + + - title: What's new in v1.1 + url: /spec/v1.1/whats-new + description: What's new in SLSA Version 1.1 + + - title: About SLSA + url: /spec/v1.1/about + description: An introductory guide to SLSA + + - title: Supply chain threats + url: /spec/v1.1/threats-overview + description: An introduction to supply chain threats + + - title: Use cases + url: /spec/v1.1/use-cases + description: Use cases + + - title: Guiding principles + url: /spec/v1.1/principles + description: Use cases + + - title: FAQ + url: /spec/v1.1/faq + description: Questions and more information + + - title: Future directions + url: /spec/v1.1/future-directions + description: Additions and changes being considered for future SLSA versions + +- title: Core specification + description: > + These pages describe SLSA's security levels and requirements for each track. + If you want to achieve SLSA a particular level, these are the requirements + you'll need to meet. + children: + + - title: Terminology + url: /spec/v1.1/terminology + description: Terminology and model used by SLSA + + - title: Security levels + url: /spec/v1.1/levels + description: Overview of SLSA's tracks and levels, intended for all audiences + + - title: Producing artifacts + url: /spec/v1.1/requirements + description: Detailed technical requirements for producing software artifacts, intended for platform implementers + + - title: Distributing provenance + url: /spec/v1.1/distributing-provenance + description: Detailed technical requirements for distributing provenance, intended for platform implementers and software distributors + + - title: Verifying artifacts + url: /spec/v1.1/verifying-artifacts + description: Guidance for verifying software artifacts and their SLSA provenance, intended for platform implementers and software consumers + + - title: Verifying build platforms + url: /spec/v1.1/verifying-systems + description: Guidelines for securing SLSA Build L3+ builders, intended for platform implementers + + - title: Threats & mitigations + url: /spec/v1.1/threats + description: Detailed information about specific supply chain attacks and how SLSA helps + +- title: Attestation formats + description: > + These pages include the concrete schemas for SLSA attestations. The + Provenance and VSA formats are recommended, but not required by the + specification. + children: + + - title: General model + url: /attestation-model + description: General attestation mode + + - title: Provenance + url: /spec/v1.1/provenance + description: Suggested provenance format and explanation + + - title: VSA + url: /spec/v1.1/verification_summary + description: Suggested VSA format and explanation + +- title: How to SLSA + description: > + These instructions tell you how to apply the core SLSA specification to use + SLSA in your specific situation. + children: + + - title: For developers + url: /get-started + description: How to apply SLSA requirements to your build + + - title: For organizations + url: /how-to-orgs + description: How to apply SLSA to an organization + + - title: For infrastructure providers + url: /how-to-infra + description: How to implement SLSA in source, build, and package platforms + +- title: Specification stages + url: /spec-stages + +- title: Community + url: /community + +- title: Blog + url: /blog + +- title: Single-page view + url: /spec/v1.1/onepage + skip_next_prev: true # don't show as a next/prev link diff --git a/docs/_data/versions.yml b/docs/_data/versions.yml index b7ec731f4..97c59bc84 100644 --- a/docs/_data/versions.yml +++ b/docs/_data/versions.yml @@ -36,3 +36,8 @@ spec: v1.0: name: Version 1.0 status: Approved + v1.1: + name: Version 1.1 (DRAFT) + status: Draft + draft: true + hidden: true diff --git a/docs/_redirects b/docs/_redirects index 28021190f..bb22239ce 100644 --- a/docs/_redirects +++ b/docs/_redirects @@ -52,6 +52,7 @@ /provenance/v1-rc1 /spec/v1.0-rc1/provenance 301 /provenance/v1-rc2 /spec/v1.0-rc2/provenance 301 /provenance/v1.0 /spec/v1.0/provenance 301 +/provenance/v1.1 /spec/v1.1/provenance 301 /spec /spec/v1.0 302 /spec/faq /spec/v1.0/faq 302 @@ -66,3 +67,4 @@ /verification_summary/v1-rc1 /spec/v1.0-rc2/verification_summary 301 /verification_summary/v1-rc2 /spec/v1.0-rc2/verification_summary 301 /verification_summary/v1.0 /spec/v1.0/verification_summary 301 +/verification_summary/v1.1 /spec/v1.1/verification_summary 301 diff --git a/docs/spec/v1.1/about.md b/docs/spec/v1.1/about.md new file mode 100644 index 000000000..0ad229800 --- /dev/null +++ b/docs/spec/v1.1/about.md @@ -0,0 +1,142 @@ +--- +title: About SLSA +description: With supply chain attacks on the rise, a shared vocabulary and universal framework is needed to provide incremental guidance to harden supply chains for more secure software production. This page introduces the main concepts behind SLSA and explains how it can help anyone involved in producing, consuming, or providing infrastructure for software. +--- + +This page is an introduction to SLSA and its concepts. If you're new +to SLSA, start here! + +## What is SLSA? + +SLSA is a set of incrementally adoptable guidelines for supply chain security, +established by industry consensus. The specification set by SLSA is useful for +both software producers and consumers: producers can follow SLSA's guidelines to +make their software supply chain more secure, and consumers can use SLSA to make +decisions about whether to trust a software package. + +SLSA offers: + +- A common vocabulary to talk about software supply chain security +- A way to secure your incoming supply chain by evaluating the trustworthiness of the artifacts you consume +- An actionable checklist to improve your own software's security +- A way to measure your efforts toward compliance with forthcoming + Executive Order standards in the [Secure Software Development Framework (SSDF)](https://csrc.nist.gov/Projects/ssdf) + +## Why SLSA is needed + +High profile attacks like those against [SolarWinds](https://www.crowdstrike.com/blog/sunspot-malware-technical-analysis/) or [Codecov](https://about.codecov.io/apr-2021-post-mortem/) have exposed the kind of supply +chain integrity weaknesses that may go unnoticed, yet quickly become very +public, disruptive, and costly in today's environment when exploited. They've +also shown that there are inherent risks not just in code itself, but at +multiple points in the complex process of getting that code into software +systems—that is, in the **software supply chain**. Since these attacks are on +the rise and show no sign of decreasing, a universal framework for hardening the +software supply chain is needed, as affirmed by the +[U.S. Executive Order on Improving the Nation's Cybersecurity](https://www.whitehouse.gov/briefing-room/presidential-actions/2021/05/12/executive-order-on-improving-the-nations-cybersecurity/). + +Security techniques for vulnerability detection and analysis of source code are +essential, but are not enough on their own. Even after fuzzing or vulnerability +scanning is completed, changes to code can happen, whether unintentionally or +from insider threats or compromised accounts. Risk for code modification exists at +each link in a typical software supply chain, from source to build through +packaging and distribution. Any weaknesses in the supply chain undermine +confidence in whether the code that you run is actually the code that you +scanned. + +SLSA is designed to support automation that tracks code handling from source +to binary, protecting against tampering regardless of the complexity +of the software supply chain. As a result, SLSA increases trust that the +analysis and review performed on source code can be assumed to still apply to +the binary consumed after the build and distribution process. + +## SLSA in layperson's terms + +There has been a [lot of discussion](https://ntia.gov/page/software-bill-materials) about the need for "ingredient labels" for +software—a "software bill of materials" (SBOM) that tells users what is in their +software. Building off this analogy, SLSA can be thought of as all the food +safety handling guidelines that make an ingredient list credible. From standards +for clean factory environments so contaminants aren't introduced in packaging +plants, to the requirement for tamper-proof seals on lids that ensure nobody +changes the contents of items sitting on grocery store shelves, the entire food +safety framework ensures that consumers can trust that the ingredient list +matches what's actually in the package they buy. + +Likewise, the SLSA framework provides this trust with guidelines and +tamper-resistant evidence for securing each step of the software production +process. That means you know not only that nothing unexpected was added to the +software product, but also that the ingredient label itself wasn't tampered with +and accurately reflects the software contents. In this way, SLSA helps protect +against the risk of: + +- Code modification (by adding a tamper-evident "seal" to code after + source control) +- Uploaded artifacts that were not built by the expected CI/CD platform (by marking + artifacts with a factory "stamp" that shows which build platform created it) +- Threats against the build platform (by providing "manufacturing facility" + best practices for build platform services) + +For more exploration of this analogy, see the blog post +[SLSA + SBOM: Accelerating SBOM success with the help of SLSA](/blog/2022/05/slsa-sbom). + +## Who is SLSA for? + +In short: everyone involved in producing and consuming software, or providing +infrastructure for software. + +**Software producers**, such as an open source project, a software vendor, or a +team writing first-party code for use within the same company. SLSA gives you +protection against tampering along the supply chain to your consumers, both +reducing insider risk and increasing confidence that the software you produce +reaches your consumers as you intended. + +**Software consumers**, such as a development team using open source packages, a +government agency using vendored software, or a CISO judging organizational +risk. SLSA gives you a way to judge the security practices of the software you +rely on and be sure that what you receive is what you expected. + +**Infrastructure providers**, who provide infrastructure such as an ecosystem +package manager, build platform, or CI/CD platform. As the bridge between the +producers and consumers, your adoption of SLSA enables a secure software supply +chain between them. + +## How SLSA works + +We talk about SLSA in terms of [tracks and levels](levels.md). +A SLSA track focuses on a particular aspect of a supply chain, such as the Build +Track. SLSA v1.0 consists of only a single track ([Build](levels.md#build-track)), but future versions of +SLSA will add tracks that cover other parts of the software supply chain, such +as how source code is managed. + +Within each track, ascending levels indicate increasingly hardened security +practices. Higher levels provide better guarantees against supply chain threats, +but come at higher implementation costs. Lower SLSA levels are designed to be +easier to adopt, but with only modest security guarantees. SLSA 0 is sometimes +used to refer to software that doesn't yet meet any SLSA level. Currently, the +SLSA Build Track encompasses Levels 1 through 3, but we envision higher levels +to be possible in [future revisions](future-directions.md). + +The combination of tracks and levels offers an easy way to discuss whether +software meets a specific set of requirements. By referring to an artifact as +meeting SLSA Build Level 3, for example, you're indicating in one phrase that +the software artifact was built following a set of security practices that +industry leaders agree protect against particular supply chain compromises. + +## What SLSA doesn't cover + +SLSA is only one part of a thorough approach to supply chain security. There +are several areas outside SLSA's current framework that are nevertheless +important to consider together with SLSA such as: + +- Code quality: SLSA does not tell you whether the developers writing the + source code followed secure coding practices. +- Producer trust: SLSA does not address organizations that intentionally + produce malicious software, but it can reduce insider risks within an + organization you trust. SLSA's Build Track protects against tampering during + or after the build, and [future SLSA tracks](future-directions.md) intend to + protect against unauthorized modifications of source code and dependencies. +- Transitive trust for dependencies: the SLSA level of an artifact is + independent of the level of its dependencies. You can use SLSA recursively to + also judge an artifact's dependencies on their own, but there is + currently no single SLSA level that applies to both an artifact and its + transitive dependencies together. For a more detailed explanation of why, + see the [FAQ](faq#q-why-is-slsa-not-transitive). diff --git a/docs/spec/v1.1/distributing-provenance.md b/docs/spec/v1.1/distributing-provenance.md new file mode 100644 index 000000000..11f01f4a2 --- /dev/null +++ b/docs/spec/v1.1/distributing-provenance.md @@ -0,0 +1,170 @@ +--- +title: Distributing provenance +description: This page covers the detailed technical requirements for distributing provenance at each SLSA level. The intended audience is platform implementers and software distributors. +--- + +In order to make provenance for artifacts available after generation +for verification, SLSA requires the distribution and verification of provenance +metadata in the form of SLSA attestations. + +This document provides specifications for distributing provenance, and the +relationship between build artifacts and provenance (build attestations). It is +primarily concerned with artifacts for ecosystems that distribute build +artifacts, but some attention is also paid to ecosystems that distribute +container images or only distribute source artifacts, as many of the same +principles generally apply to any artifact or group of artifacts. + +In addition, this document is primarily for the benefit of artifact +distributors, to understand how they can adopt the distribution of SLSA +provenance. It is primarily concerned with the means of distributing +attestations and the relationship of attestations to build artifacts, and not +with the specific format of the attestation itself. + +The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", +"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be +interpreted as described in [RFC 2119](https://www.rfc-editor.org/rfc/rfc2119). + +## Background + +The [package ecosystem]'s maintainers are responsible for reliably +redistributing artifacts and provenance, making the producers' expectations +available to consumers, and providing tools to enable safe artifact consumption +(e.g. whether an artifact meets its producer's expectations). + +## Relationship between releases and attestations + +Attestations SHOULD be bound to artifacts, not releases. + +A single "release" of a project, package, or library might include multiple +artifacts. These artifacts result from builds on different platforms, +architectures or environments. The builds need not happen at roughly the same +point in time and might even span multiple days. + +It is often difficult or impossible to determine when a release is 'finished' +because many ecosystems allow adding new artifacts to old releases when adding +support for new platforms or architectures. Therefore, the set of attestations +for a given release MAY grow over time as additional builds and attestations +are created. + +Thus, package ecosystems SHOULD support multiple individual attestations per +release. At the time of a given build, the relevant provenance for that build +can be added to the release, depending on the relationship to the given +artifacts. + +## Relationship between artifacts and attestations + +Package ecosystems SHOULD support a one-to-many relationship from build +artifacts to attestations to ensure that anyone is free to produce and publish +any attestation they might need. However, while there are lots of possible +attestations that can have a relationship to a given artifact, in this context +SLSA is primarily concerned with build attestations, i.e. provenance, and as +such, this specification only considers build attestations, produced by the +same maintainers as the artifacts themselves. + +By providing provenance alongside an artifact in the manner specified by a +given ecosystem, maintainers are considered to be 'elevating' these build +attestations above all other possible attestations that could be provided by +third parties for a given artifact. The ultimate goal is for maintainers to +provide the provenance necessary for a repository to be able to verify some +potential policy that requires a certain SLSA level for publication, not +support the publication of arbitrary attestations by third parties. + +As a result, this provenance SHOULD accompany the artifact at publish time, and +package ecosystems SHOULD provide a way to map a given artifact to its +corresponding attestations. The mappings can be either implicit (e.g. require a +custom filename schema that uniquely identifies the provenance over other +attestation types) or explicit (e.g. it could happen as a de-facto standard +based on where the attestation is published). + +The provenance SHOULD have a filename that is directly related to the build +artifact filename. For example, for an artifact `.`, the +attestation is `.attestation` or some similar extension (for example +[in-toto](https://in-toto.io/) recommends `.intoto.jsonl`.) + +## Where attestations are published + +There are a number of opportunities and venues to publish attestations during +and after the build process. Producers MUST publish attestations in at least +one place, and SHOULD publish attestations in more than one place: + +- **Publish attestations alongside the source repository releases**: If the + source repository hosting provider offers an artifact "release" feature, + such as [GitHub + releases](https://docs.github.com/en/repositories/releasing-projects-on-github/about-releases) + or [GitLab releases](https://docs.gitlab.com/ee/user/project/releases/), + producers SHOULD include provenance as part of such releases. This option + has the benefit of requiring no changes to the package registry to support + provenance formats, but has the disadvantage of putting the source + repository hosting providing in the critical path for installers that want to + verify policy at build-time. +- **Publish attestations alongside the artifact in the package registry**: + Many software repositories already support some variety of publishing 1:1 + related files alongside an artifact, sometimes known as “sidecar files”. + For example, PyPI supports publishing `.asc` files representing the PGP + signature for an artifact with the same filename (but different extension). + This option requires the mapping between artifact and attestation (or + attestation vessel) to be 1:1. +- **Publish attestations elsewhere, record their existence in a transparency + log**: Once an attestation has been generated and published for a build, a + hash of the attestation and a pointer to where it is indexed SHOULD be + published to a third-party transparency log that exists outside the source + repository and package registry. Not only are transparency logs such as + [Rekor from Sigstore](https://github.com/sigstore/rekor) guaranteed + to be immutable, but they typically also make monitoring easier. + Requiring the presence of the attestation in a monitored transparency log + during verification helps ensure the attestation is trustworthy. + +Combining these options gives us a process for bootstrapping SLSA adoption +within an ecosystem, even if the package registry doesn't support publishing +attestations. First, interested projects modify their release process to +produce SLSA provenance. Then, they publish that provenance to their source +repository. Finally, they publish the provenance to the package registry, if +and when the registry supports it. + +Long-term, package registries SHOULD support uploading and distributing +provenance alongside the artifact. This model is preferred for two reasons: + +- trust: clients already trust the package registry as the source of their + artifacts, and don't need to trust an additional service; +- reliability: clients already depend on the package registry as part of + their critical path, so distributing provenance via the registry avoids + adding an additional point of failure. + +Short term, consumers of build artifacts can bootstrap a manual policy by using +the source repository only for projects that publish all artifacts and +attestations to the source repository, and later extend this to all artifacts +published to the package registry via the canonical installation tools once +a given ecosystem supports them. + +## Immutability of attestations + +Attestations SHOULD be immutable. Once an attestation is published as it +corresponds to a given artifact, that attestation is immutable and cannot be +overwritten later with a different attestation that refers to the same +artifact. Instead, a new release (and new artifacts) SHOULD be created. + +## Format of the attestation + +The provenance is available to the consumer in a format that the consumer +accepts. The format SHOULD be in-toto [SLSA Provenance](/provenance), but +another format MAY be used if both producer and consumer agree and it meets all +the other requirements. + +## Considerations for source-based ecosystems + +Some ecosystems have support for installing directly from source repositories +(an option for Python/`pip`, Go, etc). In these cases, there is no need to +publish or verify provenance because there is no "build" step that translates +between a source repository and an artifact that is being installed. + +However, for ecosystems that install from source repositories _via_ some +intermediary (e.g. [Homebrew installing from GitHub release artifacts generated +from the repository or GitHub Packages](https://docs.brew.sh/Bottles), [Go +installing through the Go module proxy](https://proxy.golang.org/)), these +ecosystems distribute "source archives" that are not the bit-for-bit identical +form from version control. These intermediaries are transforming the original +source repository in some way that constitutes a "build" and as a result SHOULD +be providing build provenance for this "package", and the recommendations +outlined here apply. + +[package ecosystem]: verifying-artifacts.md#package-ecosystem diff --git a/docs/spec/v1.1/faq.md b/docs/spec/v1.1/faq.md new file mode 100644 index 000000000..e02ae2174 --- /dev/null +++ b/docs/spec/v1.1/faq.md @@ -0,0 +1,156 @@ +--- +title: Frequently asked questions +description: Answers to questions frequently asked about SLSA. +layout: specifications +--- + +## Q: Why is SLSA not transitive? + +SLSA Build levels only cover the trustworthiness of a single build, with no +requirements about the build levels of transitive dependencies. The reason for +this is to make the problem tractable. If a SLSA Build level required +dependencies to be the same level, then reaching a level would require starting +at the very beginning of the supply chain and working forward. This is +backwards, forcing us to work on the least risky component first and blocking +any progress further downstream. By making each artifact's SLSA rating +independent from one another, it allows parallel progress and prioritization +based on risk. (This is a lesson we learned when deploying other security +controls at scale throughout Google.) We expect SLSA ratings to be composed to +describe a supply chain's overall security stance, as described in the case +study [vision](../../example.md#vision-case-study). + +## Q: What about reproducible builds? + +When talking about [reproducible builds](https://reproducible-builds.org), there +are two related but distinct concepts: "reproducible" and "verified +reproducible." + +"Reproducible" means that repeating the build with the same inputs results in +bit-for-bit identical output. This property +[provides](https://reproducible-builds.org/docs/buy-in/) +[many](https://wiki.debian.org/ReproducibleBuilds/About) +[benefits](https://google.github.io/building-secure-and-reliable-systems/raw/ch14.html#hermeticcomma_reproduciblecomma_or_veri), +including easier debugging, more confident cherry-pick releases, better build +caching and storage efficiency, and accurate dependency tracking. + +"Verified reproducible" means using two or more independent build platforms to +corroborate the provenance of a build. In this way, one can create an overall +platform that is more trustworthy than any of the individual components. This is +often +[suggested](https://www.linuxfoundation.org/en/blog/preventing-supply-chain-attacks-like-solarwinds/) +as a solution to supply chain integrity. Indeed, this is one option to secure +build steps of a supply chain. When designed correctly, such a platform can +satisfy all of the SLSA Build level requirements. + +That said, verified reproducible builds are not a complete solution to supply +chain integrity, nor are they practical in all cases: + +- Reproducible builds do not address source, dependency, or distribution + threats. +- Reproducers must truly be independent, lest they all be susceptible to the + same attack. For example, if all rebuilders run the same pipeline software, + and that software has a vulnerability that can be triggered by sending a + build request, then an attacker can compromise all rebuilders, violating the + assumption above. +- Some builds cannot easily be made reproducible, as noted above. +- Closed-source reproducible builds require the code owner to either grant + source access to multiple independent rebuilders, which is unacceptable in + many cases, or develop multiple, independent in-house rebuilders, which is + likely prohibitively expensive. + +Therefore, SLSA does not require verified reproducible builds directly. Instead, +verified reproducible builds are one option for implementing the requirements. + +For more on reproducibility, see +[Hermetic, Reproducible, or Verifiable?](https://google.github.io/building-secure-and-reliable-systems/raw/ch14.html#hermeticcomma_reproduciblecomma_or_veri) + +## Q: How does SLSA relate to in-toto? + +[in-toto](https://in-toto.io/) is a framework to secure software supply chains +hosted at the [Cloud Native Computing Foundation](https://cncf.io/). The in-toto +specification provides a generalized workflow to secure different steps in a +software supply chain. The SLSA specification recommends +[in-toto attestations](https://github.com/in-toto/attestation) as the vehicle to +express Provenance and other attributes of software supply chains. Thus, in-toto +can be thought of as the unopinionated layer to express information pertaining +to a software supply chain, and SLSA as the opinionated layer specifying exactly +what information must be captured in in-toto metadata to achieve the guarantees +of a particular level. + +in-toto's official implementations written in +[Go](https://github.com/in-toto/in-toto-golang), +[Java](https://github.com/in-toto/in-toto-java), and +[Rust](https://github.com/in-toto/in-toto-rs) include support for generating +SLSA Provenance metadata. These APIs are used in other tools generating SLSA +Provenance such as Sigstore's cosign, the SLSA GitHub Generator, and the in-toto +Jenkins plugin. + +## Q. What is the difference between a build platform, system, and service? + +Build platform and build system have been used interchangably in the past. With +the v1.0 specification, however, there has been a unification around the term +platform as indicated in the [Terminology](terminology.md). The use of the word +`system` still exists related to software and services within the build platform +and to systems outside of a build platform like change management systems. + +A build service is a hosted build platform that is often run on shared infrastructure +instead of individuals' machines and workstations. Its use has also been replaced outside +of the requirements as it relates to the build platform. + +## Q: Is SLSA the same as TACOS? + +No. +[Trusted Attestation and Compliance for Open Source (TACOS)](https://github.com/tacosframework) +is a framework authored by Tidelift. +Per their website, TACOS is a framework +"for assessing the development practices of open source projects +against a set of secure development standards specified by the (US) +NIST Secure Software Development Framework (SSDF) V1.1" which +"vendors can use to provide self-attestation for the open source components +they rely on." + +In contrast, SLSA is a community-developed framework---including +adoptable guidelines for securing a software supply chain and +mechanism to evaluate the trustworthiness of artifacts you consume---that +is part of the Open Source Security Foundation (OpenSSF). + +## Q: How does SLSA and SLSA Provenance relate to SBOM? + +[Software Bill of Materials (SBOM)] are a frequently recommended tool for +increased software supply chain rigor. An SBOM is typically focused on +understanding software in order to evaluate risk through known vulnerabilities +and license compliance. These use-cases require fine-grained and timely data +which can be refined to improve signal-to-noise ratio. + +[SLSA Provenance] and the [Build track] are focused on trustworthiness of the +build process. To improve trustworthiness, Provenance is generated in the build +platform's trusted control plane, which in practice results in it being coarse +grained. For example, in Provenance metadata completeness of +`resolvedDependencies` information is on a best-effort basis. Further, the +`ResourceDescriptor` type does not require version and license information or +even a URI to the dependency's original location. + +While they likely include similar data, SBOMs and SLSA Provenance operate at +different levels of abstraction. The fine-grained data in an SBOM typically +describes the components present in a produced artifact, whereas SLSA +Provenance more coarsely describes parameters of a build which are external to +the build platform. + +The granularity and expressiveness of the two use-cases differs enough that +current SBOM formats were deemed not a good fit for the requirements of +the Build track. Yet SBOMs are a good practice and may form part of a future +SLSA Vulnerabilities track. Further, SLSA Provenance can increase the +trustworthiness of an SBOM by describing how the SBOM was created. + +SLSA Provenance, the wider [in-toto Attestation Framework] in which the +recommended format sits, and the various SBOM standards, are all rapidly +evolving spaces. There is ongoing investigation into linking between the +different formats and exploration of alignment on common models. This FAQ entry +describes our understanding of the intersection efforts today. We do not know +how things will evolve over the coming months and years, but we look forward to +the collaboration and improved software supply chain security. + +[Software Bill of Materials (SBOM)]: https://ntia.gov/sbom +[SLSA Provenance]: provenance.md +[Build track]: levels.md#build-track +[in-toto Attestation Framework]: https://github.com/in-toto/attestation/blob/main/spec/ diff --git a/docs/spec/v1.1/future-directions.md b/docs/spec/v1.1/future-directions.md new file mode 100644 index 000000000..bfa8cc45f --- /dev/null +++ b/docs/spec/v1.1/future-directions.md @@ -0,0 +1,77 @@ +--- +title: Future directions +description: The initial draft version (v0.1) of SLSA had a larger scope including protections against tampering with source code and a higher level of build integrity (Build L4). This page collects some early thoughts on how SLSA **might** evolve in future versios to re-introduce these notions and add other additional aspects of automatable supply chain security. +--- + +The initial [draft version (v0.1)] of SLSA had a larger scope including +protections against tampering with source code and a higher level of build +integrity (Build L4). This page collects some early thoughts on how SLSA +**might** evolve in future versions to re-introduce those notions and add other +additional aspects of automatable supply chain security. + +
+ +## Build track + +### Build L4 + +A build L4 could include further hardening of the build platform and enabling +corraboration of the provenance, for example by providing complete knowledge of +the build inputs. + +The initial [draft version (v0.1)] of SLSA defined a "SLSA 4" that included the +following requirements, which **may or may not** be part of a future Build L4: + +- Pinned dependencies, which guarantee that each build runs on exactly the + same set of inputs. +- Hermetic builds, which guarantee that no extraneous dependencies are used. +- All dependencies listed in the provenance, which enables downstream verifiers + to recursively apply SLSA to dependencies. +- Reproducible builds, which enable other build platforms to corroborate the + provenance. + +
+ +
+ +## Source track + +A Source track could provide protection against tampering of the source code +prior to the build. + +The initial [draft version (v0.1)](../v0.1/requirements.md#source-requirements) +of SLSA included the following source requirements, which **may or may not** +form the basis for a future Source track: + +- Strong authentication of author and reviewer identities, such as 2-factor + authentication using a hardware security key, to resist account and + credential compromise. +- Retention of the source code to allow for after-the-fact inspection and + future rebuilds. +- Mandatory two-person review of all changes to the source to prevent a single + compromised actor or account from introducing malicious changes. + +
+ +
+ +## Build Platform Operations track + +A Build Platform Operations track could provide assurances around the hardening +of build platforms as they are operated. + +The initial [draft version (v0.1)] of SLSA included a section on +[common requirements](../v0.1/requirements.md#common-requirements) that formed +the foundation of the guidance for +[verifying build systems](verifying-systems.md), which **may or may not** form +the basis for a future Build Platform Operations track: + +- Controls for approval, logging, and auditing of all physical and remote + access to platform infrastructure, cryptographic secrets, and privileged + debugging interfaces. +- Conformance to security best practices to minimize the risk of compromise. +- Protection of cryptographic secrets used by the build platform. + +
+ +[draft version (v0.1)]: ../v0.1/requirements.md diff --git a/docs/spec/v1.1/images/build-model.svg b/docs/spec/v1.1/images/build-model.svg new file mode 100644 index 000000000..9d6bed6ca --- /dev/null +++ b/docs/spec/v1.1/images/build-model.svg @@ -0,0 +1 @@ + \ No newline at end of file diff --git a/docs/spec/v1.1/images/provenance-model.svg b/docs/spec/v1.1/images/provenance-model.svg new file mode 100644 index 000000000..028dad49e --- /dev/null +++ b/docs/spec/v1.1/images/provenance-model.svg @@ -0,0 +1 @@ + \ No newline at end of file diff --git a/docs/spec/v1.1/images/supply-chain-model.svg b/docs/spec/v1.1/images/supply-chain-model.svg new file mode 100644 index 000000000..d3efece68 --- /dev/null +++ b/docs/spec/v1.1/images/supply-chain-model.svg @@ -0,0 +1,28 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/docs/spec/v1.1/images/supply-chain-threats-build-verification.svg b/docs/spec/v1.1/images/supply-chain-threats-build-verification.svg new file mode 100644 index 000000000..25e577645 --- /dev/null +++ b/docs/spec/v1.1/images/supply-chain-threats-build-verification.svg @@ -0,0 +1,84 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/docs/spec/v1.1/images/supply-chain-threats.svg b/docs/spec/v1.1/images/supply-chain-threats.svg new file mode 100644 index 000000000..0e70413b0 --- /dev/null +++ b/docs/spec/v1.1/images/supply-chain-threats.svg @@ -0,0 +1,77 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/docs/spec/v1.1/images/verification-model.svg b/docs/spec/v1.1/images/verification-model.svg new file mode 100644 index 000000000..a29507e08 --- /dev/null +++ b/docs/spec/v1.1/images/verification-model.svg @@ -0,0 +1 @@ + \ No newline at end of file diff --git a/docs/spec/v1.1/index.md b/docs/spec/v1.1/index.md new file mode 100644 index 000000000..ea7abe5bc --- /dev/null +++ b/docs/spec/v1.1/index.md @@ -0,0 +1,27 @@ +--- +title: SLSA specification +description: SLSA is a specification for describing and incrementally improving supply chain security, established by industry consensus. It is organized into a series of levels that describe increasing security guarantees. This is **version 1.0** of the SLSA specification, which defines the SLSA levels. +--- + +SLSA is a specification for describing and incrementally improving supply chain +security, established by industry consensus. It is organized into a series of +levels that describe increasing security guarantees. + +This is **version 1.0** of the SLSA specification, which defines the SLSA +levels and recommended attestation formats, including provenance. + +{%- for section in site.data.nav.v10 %} +{%- if section.children %} + +## {{ section.title }} + +{{ section.description }} + +| Page | Description | +| ---- | ----------- | +{%- for child in section.children %} +| [{{child.title}}]({{child.url | relative_url}}) | {{child.description}} | +{%- endfor %} + +{%- endif %} +{%- endfor %} diff --git a/docs/spec/v1.1/levels.md b/docs/spec/v1.1/levels.md new file mode 100644 index 000000000..22b5b6522 --- /dev/null +++ b/docs/spec/v1.1/levels.md @@ -0,0 +1,235 @@ +--- +title: Security levels +description: SLSA is organized into a series of levels that provide increasing supply chain security guarantees. This gives you confidence that software hasn’t been tampered with and can be securely traced back to its source. This page is a descriptive overview of the SLSA levels and tracks, describing their intent. +--- + +SLSA is organized into a series of levels that provide increasing supply chain +security guarantees. This gives you confidence that software hasn’t been +tampered with and can be securely traced back to its source. + +This page is a descriptive overview of the SLSA levels and tracks, describing +their intent. For the prescriptive requirements for each level, see +[Requirements](requirements.md). For a general overview of SLSA, see +[About SLSA](principles.md). + +## Levels and tracks + +SLSA levels are split into *tracks*. Each track has its own set of levels that +measure a particular aspect of supply chain security. The purpose of tracks is +to recognize progress made in one aspect of security without blocking on an +unrelated aspect. Tracks also allow the SLSA spec to evolve: we can add more +tracks without invalidating previous levels. + +| Track/Level | Requirements | Focus | +| ----------- | ------------ | ----- | +| [Build L0] | (none) | (n/a) | +| [Build L1] | Provenance showing how the package was built | Mistakes, documentation | +| [Build L2] | Signed provenance, generated by a hosted build platform | Tampering after the build | +| [Build L3] | Hardened build platform | Tampering during the build | + + + +> Note: The [previous version] of the specification used a single unnamed track, +> SLSA 1–4. For version 1.0 the Source aspects were removed to focus on the +> Build track. A Source track may be added in [future versions]. + +## 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](threats.md). + +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](requirements.md). + +
+ +### Build L0: No guarantees + +
+
Summary
+ +No requirements---L0 represents the lack of SLSA. + +
Intended for
+ +Development or test builds of software that are built and run on the same +machine, such as unit tests. + +
Requirements
+ +n/a + +
Benefits
+ +n/a + +
+
+
+ +### Build L1: Provenance exists + +
+
Summary
+ +Package has provenance showing how it was built. Can be used to prevent mistakes +but is trivial to bypass or forge. + +
Intended for
+ +Projects and organizations wanting to easily and quickly gain some benefits of +SLSA---other than tamper protection---without changing their build workflows. + +
Requirements
+ +- Software producer follows a consistent build process so that others can form + expectations about what a "correct" build looks like. + +- Build platform automatically generates [provenance] describing how the + artifact was built, including: what entity built the package, what build + process they used, and what the top-level input to the build were. + +- Software producer distributes provenance to consumers, preferably using a + convention determined by the package ecosystem. + +
Benefits
+ +- Makes it easier for both producers and consumers to debug, patch, rebuild, + and/or analyze the software by knowing its precise source version and build + process. + +- With [verification], prevents mistakes during the release process, such as + building from a commit that is not present in the upstream repo. + +- Aids organizations in creating an inventory of software and build platforms + used across a variety of teams. + +
Notes
+ +- Provenance may be incomplete and/or unsigned at L1. Higher levels require + more complete and trustworthy provenance. + +
+ +
+
+ +### Build L2: Hosted build platform + +
+
Summary
+ +Forging the provenance or evading verification requires an explicit "attack", +though this may be easy to perform. Deters unsophisticated adversaries or those +who face legal or financial risk. + +In practice, this means that builds run on a hosted platform that generates and +signs[^sign] the provenance. + +
Intended for
+ +Projects and organizations wanting to gain moderate security benefits of SLSA by +switching to a hosted build platform, while waiting for changes to the build +platform itself required by [Build L3]. + +
Requirements
+ +All of [Build L1], plus: + +- The build runs on a hosted build platform that generates and signs[^sign] the + provenance itself. This may be the original build, an after-the-fact + reproducible build, or some equivalent platform that ensures the + trustworthiness of the provenance. + +- Downstream verification of provenance includes validating the authenticity + of the provenance. + +
Benefits
+ +All of [Build L1], plus: + +- Prevents tampering after the build through digital signatures[^sign]. + +- Deters adversaries who face legal or financial risk by evading security + controls, such as employees who face risk of getting fired. + +- Reduces attack surface by limiting builds to specific build platforms that + can be audited and hardened. + +- Allows large-scale migration of teams to supported build platforms early + while further hardening work ([Build L3]) is done in parallel. + +
+
+
+ +[^sign]: Alternate means of verifying the authenticity of the provenance are + also acceptable. + +### Build L3: Hardened builds + +
+
Summary
+ +Forging the provenance or evading verification requires exploiting a +vulnerability that is beyond the capabilities of most adversaries. + +In practice, this means that builds run on a hardened build platform that offers +strong tamper protection. + +
Intended for
+ +Most software releases. Build L3 usually requires significant changes to +existing build platforms. + +
Requirements
+ +All of [Build L2], plus: + +- Build platform implements strong controls to: + + - prevent runs from influencing one another, even within the same project. + - prevent secret material used to sign the provenance from being + accessible to the user-defined build steps. + +
Benefits
+ +All of [Build L2], plus: + +- Prevents tampering during the build---by insider threats, compromised + credentials, or other tenants. + +- Greatly reduces the impact of compromised package upload credentials by + requiring attacker to perform a difficult exploit of the build process. + +- Provides strong confidence that the package was built from the official + source and build process. + +
+
+ + + +[build l0]: #build-l0 +[build l1]: #build-l1 +[build l2]: #build-l2 +[build l3]: #build-l3 +[future versions]: future-directions.md +[previous version]: ../v0.1/levels.md +[provenance]: terminology.md +[verification]: verifying-artifacts.md diff --git a/docs/spec/v1.1/onepage.md b/docs/spec/v1.1/onepage.md new file mode 100644 index 000000000..8e895eadb --- /dev/null +++ b/docs/spec/v1.1/onepage.md @@ -0,0 +1,13 @@ +--- +title: SLSA Specification +description: A one-page rendering of all that is included in SLSA v1.0. +noindex: true +--- +{%- comment -%} +A single page containing all the following files as different sections +{%- endcomment -%} + +{% assign dir = "/spec/v1.0/" %} +{% assign filenames = "whats-new,about,threats-overview,use-cases,principles,faq,future-directions,terminology,levels,requirements,distributing-provenance,verifying-systems,verifying-artifacts,threats,provenance,verification_summary" %} + +{% include onepage.liquid dir=dir filenames=filenames %} diff --git a/docs/spec/v1.1/principles.md b/docs/spec/v1.1/principles.md new file mode 100644 index 000000000..359dac788 --- /dev/null +++ b/docs/spec/v1.1/principles.md @@ -0,0 +1,82 @@ +--- +title: Guiding principles +description: An introduction to the guiding principles behind SLSA's design decisions. +--- + +This page is an introduction to the guiding principles behind SLSA's design +decisions. + +## Trust platforms, verify artifacts + +Establish trust in a small number of platforms and systems---such as change management, build, +and packaging platforms---and then automatically verify the many artifacts +produced by those platforms. + +**Reasoning**: Trusted computing bases are unavoidable---there's no choice but +to trust some platforms. Hardening and verifying platforms is difficult and +expensive manual work, and each trusted platform expands the attack surface of the +supply chain. Verifying that an artifact is produced by a trusted platform, +though, is easy to automate. + +To simultaneously scale and reduce attack surfaces, it is most efficient to trust a limited +numbers of platforms and then automate verification of the artifacts produced by those platforms. +The attack surface and work to establish trust does not scale with the number of artifacts produced, +as happens when artifacts each use a different trusted platform. + +**Benefits**: Allows SLSA to scale to entire ecosystems or organizations with a near-constant +amount of central work. + +### Example + +A security engineer analyzes the architecture and implementation of a build +platform to ensure that it meets the SLSA Build Track requirements. Following the +analysis, the public keys used by the build platform to sign provenance are +"trusted" up to the given SLSA level. Downstream platforms verify the provenance +signed by the public key to automatically determine that an artifact meets the +SLSA level. + +### Corollary: Minimize the number of trusted platforms + +A corollary to this principle is to minimize the size of the trusted computing +base. Every platform we trust adds attack surface and increases the need for +manual security analysis. Where possible: + +- Concentrate trust in shared infrastructure. For example, instead of each + team within an organization maintaining their own build platform, use a + shared build platform. Hardening work can be shared across all teams. +- Remove the need to trust components. For example, use end-to-end signing + to avoid the need to trust intermediate distribution platforms. + +## Trust code, not individuals + +Securely trace all software back to source code rather than trust individuals who have write access to package registries. + +**Reasoning**: Code is static and analyzable. People, on the other hand, are prone to mistakes, +credential compromise, and sometimes malicious action. + +**Benefits**: Removes the possibility for a trusted individual---or an +attacker abusing compromised credentials---to tamper with source code +after it has been committed. + +## Prefer attestations over inferences + +Require explicit attestations about an artifact's provenance; do not infer +security properties from a platform's configurations. + +**Reasoning**: Theoretically, access control can be configured so that the only path from +source to release is through the official channels: the CI/CD platform pulls only +from the proper source, package registry allows access only to the CI/CD platform, +and so on. We might infer that we can trust artifacts produced by these platforms +based on the platform's configuration. + +In practice, though, these configurations are almost impossible to get right and +keep right. There are often over-provisioning, confused deputy problems, or +mistakes. Even if a platform is configured properly at one moment, it might not +stay that way, and humans almost always end up getting in the access control +lists. + +Access control is still important, but SLSA goes further to provide defense in depth: it **requires proof in +the form of attestations that the package was built correctly**. + +**Benefits**: The attestation removes intermediate platforms from the trust base and ensures that +individuals who are accidentally granted access do not have sufficient permission to tamper with the package. diff --git a/docs/spec/v1.1/provenance.md b/docs/spec/v1.1/provenance.md new file mode 100644 index 000000000..a533f3ca2 --- /dev/null +++ b/docs/spec/v1.1/provenance.md @@ -0,0 +1,586 @@ +--- +title: Provenance +description: Description of SLSA provenance specification for verifying where, when, and how something was produced. +layout: standard +--- +To trace software back to the source and define the moving parts in a complex +supply chain, provenance needs to be there from the very beginning. It's the +verifiable information about software artifacts describing where, when and how +something was produced. For higher SLSA levels and more resilient integrity +guarantees, provenance requirements are stricter and need a deeper, more +technical understanding of the predicate. + +This document defines the following predicate type within the [in-toto +attestation] framework: + +```json +"predicateType": "https://slsa.dev/provenance/v1" +``` + +> Important: Always use the above string for `predicateType` rather than what is +> in the URL bar. The `predicateType` URI will always resolve to the latest +> minor version of this specification. See [parsing rules](#parsing-rules) for +> more information. + +The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", +"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be +interpreted as described in [RFC 2119](https://www.rfc-editor.org/rfc/rfc2119). + +## Purpose + +Describe how an artifact or set of artifacts was produced so that: + +- Consumers of the provenance can verify that the artifact was built according + to expectations. +- Others can rebuild the artifact, if desired. + +This predicate is the RECOMMENDED way to satisfy the SLSA v1.0 [provenance +requirements](requirements#provenance-generation). + +## Model + +Provenance is an attestation that a particular build platform produced a set of +software artifacts through execution of the `buildDefinition`. + +![Build Model](images/provenance-model.svg) + +The model is as follows: + +- Each build runs as an independent process on a multi-tenant build platform. + The `builder.id` identifies this platform, representing the transitive + closure of all entities that are [trusted] to faithfully run the build and + record the provenance. (Note: The same model can be used for platform-less + or single-tenant build platforms.) + + - The build platform implementer SHOULD define a security model for the build + platform in order to clearly identify the platform's boundaries, actors, + and interfaces. This model SHOULD then be used to identify the transitive + closure of the trusted build platform for the `builder.id` as well as the + trusted control plane. + +- The build process is defined by a parameterized template, identified by + `buildType`. This encapsulates the process that ran, regardless of what + platform ran it. Often the build type is specific to the build platform + because most build platforms have their own unique interfaces. + +- All top-level, independent inputs are captured by the parameters to the + template. There are two types of parameters: + + - `externalParameters`: the external interface to the build. In SLSA, + these values are untrusted; they MUST be included in the provenance and + MUST be verified downstream. + + - `internalParameters`: set internally by the platform. In SLSA, these + values are trusted because the platform is trusted; they are OPTIONAL + and need not be verified downstream. They MAY be included to enable + reproducible builds, debugging, or incident response. + +- All artifacts fetched during initialization or execution of the build + process are considered dependencies, including those referenced directly by + parameters. The `resolvedDependencies` captures these dependencies, if + known. For example, a build that takes a git repository URI as a parameter + might record the specific git commit that the URI resolved to as a + dependency. + +- During execution, the build process might communicate with the build + platform's control plane and/or build caches. This communication is not + captured directly in the provenance, but is instead implied by `builder.id` + and subject to [SLSA Requirements](requirements.md). Such + communication SHOULD NOT influence the definition of the build; if it does, + it SHOULD go in `resolvedDependencies` instead. + +- Finally, the build process outputs one or more artifacts, identified by + `subject`. + +For concrete examples, see [index of build types](#index-of-build-types). + +## Parsing rules + +This predicate follows the in-toto attestation [parsing rules]. Summary: + +- Consumers MUST ignore unrecognized fields unless otherwise noted. +- The `predicateType` URI includes the major version number and will always + change whenever there is a backwards incompatible change. +- Minor version changes are always backwards compatible and "monotonic." + Such changes do not update the `predicateType`. +- Unset, null, and empty field values MUST be interpreted equivalently. + +## Schema + +*NOTE: This section describes the fields within `predicate`. For a description +of the other top-level fields, such as `subject`, see [Statement].* + + + +```javascript +{% include_relative schema/provenance.cue %} +``` + +
+Protocol buffer schema + +Link: [provenance.proto](schema/provenance.proto) + +```proto +{% include_relative schema/provenance.proto %} +``` + +
+ +### Provenance + +[Provenance]: #provenance + +REQUIRED for SLSA Build L1: `buildDefinition`, `runDetails` + + +
FieldTypeDescription + +
buildDefinition +BuildDefinition + +The input to the build. The accuracy and completeness are implied by +`runDetails.builder.id`. + +
runDetails +RunDetails + +Details specific to this particular execution of the build. + +
+ +### BuildDefinition + +[BuildDefinition]: #builddefinition + +REQUIRED for SLSA Build L1: `buildType`, `externalParameters` + + +
FieldTypeDescription + +
buildType +string (TypeURI) + +Identifies the template for how to perform the build and interpret the +parameters and dependencies. + +The URI SHOULD resolve to a human-readable specification that includes: overall +description of the build type; schema for `externalParameters` and +`internalParameters`; unambiguous instructions for how to initiate the build given +this BuildDefinition, and a complete example. Example: +https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1 + +
externalParameters +object + +The parameters that are under external control, such as those set by a user or +tenant of the build platform. They MUST be complete at SLSA Build L3, meaning that +that there is no additional mechanism for an external party to influence the +build. (At lower SLSA Build levels, the completeness MAY be best effort.) + +The build platform SHOULD be designed to minimize the size and complexity of +`externalParameters`, in order to reduce fragility and ease [verification]. +Consumers SHOULD have an expectation of what "good" looks like; the more +information that they need to check, the harder that task becomes. + +Verifiers SHOULD reject unrecognized or unexpected fields within +`externalParameters`. + +
internalParameters +object + +The parameters that are under the control of the entity represented by +`builder.id`. The primary intention of this field is for debugging, incident +response, and vulnerability management. The values here MAY be necessary for +reproducing the build. There is no need to [verify][Verification] these +parameters because the build platform is already trusted, and in many cases it is +not practical to do so. + +
resolvedDependencies +array (ResourceDescriptor) + +Unordered collection of artifacts needed at build time. Completeness is best +effort, at least through SLSA Build L3. For example, if the build script +fetches and executes "example.com/foo.sh", which in turn fetches +"example.com/bar.tar.gz", then both "foo.sh" and "bar.tar.gz" SHOULD be +listed here. + +
+ +The BuildDefinition describes all of the inputs to the build. It SHOULD contain +all the information necessary and sufficient to initialize the build and begin +execution. + +The `externalParameters` and `internalParameters` are the top-level inputs to the +template, meaning inputs not derived from another input. Each is an arbitrary +JSON object, though it is RECOMMENDED to keep the structure simple with string +values to aid verification. The same field name SHOULD NOT be used for both +`externalParameters` and `internalParameters`. + +The parameters SHOULD only contain the actual values passed in through the +interface to the build platform. Metadata about those parameter values, +particularly digests of artifacts referenced by those parameters, SHOULD instead +go in `resolvedDependencies`. The documentation for `buildType` SHOULD explain +how to convert from a parameter to the dependency `uri`. For example: + +```json +"externalParameters": { + "repository": "https://github.com/octocat/hello-world", + "ref": "refs/heads/main" +}, +"resolvedDependencies": [{ + "uri": "git+https://github.com/octocat/hello-world@refs/heads/main", + "digest": {"gitCommit": "7fd1a60b01f91b314f59955a4e4d4e80d8edf11d"} +}] +``` + +Guidelines: + +- Maximize the amount of information that is implicit from the meaning of + `buildType`. In particular, any value that is boilerplate and the same + for every build SHOULD be implicit. + +- Reduce parameters by moving configuration to input artifacts whenever + possible. For example, instead of passing in compiler flags via an external + parameter that has to be [verified][Verification] separately, require the + flags to live next to the source code or build configuration so that + verifying the latter automatically verifies the compiler flags. + +- In some cases, additional external parameters might exist that do not impact + the behavior of the build, such as a deadline or priority. These extra + parameters SHOULD be excluded from the provenance after careful analysis + that they indeed pose no security impact. + +- If possible, architect the build platform to use this definition as its + sole top-level input, in order to guarantee that the information is + sufficient to run the build. + +- When build configuration is evaluated client-side before being sent to the + server, such as transforming version-controlled YAML into ephemeral JSON, + some solution is needed to make [verification] practical. Consumers need a + way to know what configuration is expected and the usual way to do that is + to map it back to version control, but that is not possible if the server + cannot verify the configuration's origins. Possible solutions: + + - (RECOMMENDED) Rearchitect the build platform to read configuration + directly from version control, recording the server-verified URI in + `externalParameters` and the digest in `resolvedDependencies`. + + - Record the digest in the provenance[^digest-param] and use a separate + provenance attestation to link that digest back to version control. In + this solution, the client-side evaluation is considered a separate + "build" that SHOULD be independently secured using SLSA, though securing + it can be difficult since it usually runs on an untrusted workstation. + +- The purpose of `resolvedDependencies` is to facilitate recursive analysis of + the software supply chain. Where practical, it is valuable to record the + URI and digest of artifacts that, if compromised, could impact the build. At + SLSA Build L3, completeness is considered "best effort". + +[^digest-param]: The `externalParameters` SHOULD reflect reality. If clients + send the evaluated configuration object directly to the build server, record + the digest directly in `externalParameters`. If clients upload the + configuration object to a temporary storage location and send that location + to the build server, record the location in `externalParameters` as a URI + and record the `uri` and `digest` in `resolvedDependencies`. + +### RunDetails + +[RunDetails]: #rundetails + +REQUIRED for SLSA Build L1: `builder` + + +
FieldTypeDescription + +
builder +Builder + +Identifies the build platform that executed the invocation, which is trusted to +have correctly performed the operation and populated this provenance. + +
metadata +BuildMetadata + +Metadata about this particular execution of the build. + +
byproducts +array (ResourceDescriptor) + +Additional artifacts generated during the build that are not considered +the "output" of the build but that might be needed during debugging or +incident response. For example, this might reference logs generated during +the build and/or a digest of the fully evaluated build configuration. + +In most cases, this SHOULD NOT contain all intermediate files generated during +the build. Instead, this SHOULD only contain files that are likely to be useful +later and that cannot be easily reproduced. + +
+ +### Builder + +[Builder]: #builder + +REQUIRED for SLSA Build L1: `id` + + +
FieldTypeDescription + +
id +string (TypeURI) + +URI indicating the transitive closure of the trusted build platform. This is +[intended](/spec/v1.0/verifying-artifacts#step-1-check-slsa-build-level) +to be the sole determiner of the SLSA Build level. + +If a build platform has multiple modes of operations that have differing +security attributes or SLSA Build levels, each mode MUST have a different +`builder.id` and SHOULD have a different signer identity. This is to minimize +the risk that a less secure mode compromises a more secure one. + +The `builder.id` URI SHOULD resolve to documentation explaining: + +- The scope of what this ID represents. +- The claimed SLSA Build level. +- The accuracy and completeness guarantees of the fields in the provenance. +- Any fields that are generated by the tenant-controlled build process and not + verified by the trusted control plane, except for the `subject`. +- The interpretation of any extension fields. + +
builderDependencies +array (ResourceDescriptor) + +Dependencies used by the orchestrator that are not run within the workload +and that do not affect the build, but might affect the provenance generation +or security guarantees. + +
version +map (string→string) + +Map of names of components of the build platform to their version. + +
+ +The build platform, or builder for short, represents the transitive +closure of all the entities that are, by necessity, [trusted] to faithfully run +the build and record the provenance. This includes not only the software but the +hardware and people involved in running the service. For example, a particular +instance of [Tekton](https://tekton.dev/) could be a build platform, while +Tekton itself is not. For more info, see [Build +model](/spec/v1.0/terminology#build-model). + +The `id` MUST reflect the trust base that consumers care about. How detailed to +be is a judgement call. For example, GitHub Actions supports both GitHub-hosted +runners and self-hosted runners. The GitHub-hosted runner might be a single +identity because it's all GitHub from the consumer's perspective. Meanwhile, +each self-hosted runner might have its own identity because not all runners are +trusted by all consumers. + +Consumers MUST accept only specific signer-builder pairs. For example, "GitHub" +can sign provenance for the "GitHub Actions" builder, and "Google" can sign +provenance for the "Google Cloud Build" builder, but "GitHub" cannot sign for +the "Google Cloud Build" builder. + +Design rationale: The builder is distinct from the signer in order to support +the case where one signer generates attestations for more than one builder, as +in the GitHub Actions example above. The field is REQUIRED, even if it is +implicit from the signer, to aid readability and debugging. It is an object to +allow additional fields in the future, in case one URI is not sufficient. + +### BuildMetadata + +[BuildMetadata]: #buildmetadata + +REQUIRED: (none) + + +
FieldTypeDescription + +
invocationId +string + +Identifies this particular build invocation, which can be useful for finding +associated logs or other ad-hoc analysis. The exact meaning and format is +defined by `builder.id`; by default it is treated as opaque and case-sensitive. +The value SHOULD be globally unique. + +
startedOn +string (Timestamp) + +The timestamp of when the build started. + +
finishedOn +string (Timestamp) + +The timestamp of when the build completed. + +
+ +### Extension fields + +[Extension fields]: #extension-fields + +Implementations MAY add extension fields to any JSON object to describe +information that is not captured in a standard field. Guidelines: + +- Extension fields SHOULD use names of the form `_`, e.g. + `examplebuilder_isCodeReviewed`. This practice avoids field name collisions + by namespacing each vendor. Non-extension field names never contain an + underscore. +- Extension fields MUST NOT alter the meaning of any other field. In other + words, an attestation with an absent extension field MUST be interpreted + identically to an attestation with an unrecognized (and thus ignored) + extension field. +- Extension fields SHOULD follow the [monotonic principle][parsing rules], + meaning that deleting or ignoring the extension SHOULD NOT turn a DENY + decision into an ALLOW. + +## Verification + +[Verification]: /spec/v1.0/verifying-artifacts + +Please see [Verifying Artifacts][Verification] for a detailed discussion of +provenance verification. + +## Index of build types + +The following is a partial index of build type definitions. Each contains a +complete example predicate. + + + +- [GitHub Actions Workflow (community-maintained)](https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1) +- [Google Cloud Build (community-maintained)](https://slsa-framework.github.io/gcb-buildtypes/triggered-build/v1) + +To add an entry here, please send a pull request on GitHub. + +## Migrating from 0.2 + +To migrate from [version 0.2](/provenance/v0.2) (`old`), use the following +pseudocode. The meaning of each field is unchanged unless otherwise noted. + +```javascript +{ + "buildDefinition": { + // The `buildType` MUST be updated for v1.0 to describe how to + // interpret `inputArtifacts`. + "buildType": /* updated version of */ old.buildType, + "externalParameters": + old.invocation.parameters + { + // It is RECOMMENDED to rename "entryPoint" to something more + // descriptive. + "entryPoint": old.invocation.configSource.entryPoint, + // It is OPTIONAL to rename "source" to something more descriptive, + // especially if "source" is ambiguous or confusing. + "source": old.invocation.configSource.uri, + }, + "internalParameters": old.invocation.environment, + "resolvedDependencies": + old.materials + [ + { + "uri": old.invocation.configSource.uri, + "digest": old.invocation.configSource.digest, + } + ] + }, + "runDetails": { + "builder": { + "id": old.builder.id, + "builderDependencies": null, // not in v0.2 + "version": null, // not in v0.2 + }, + "metadata": { + "invocationId": old.metadata.buildInvocationId, + "startedOn": old.metadata.buildStartedOn, + "finishedOn": old.metadata.buildFinishedOn, + }, + "byproducts": null, // not in v0.2 + }, +} +``` + +The following fields from v0.2 are no longer present in v1.0: + +- `entryPoint`: Use `externalParameters[]` instead. +- `buildConfig`: No longer inlined into the provenance. Instead, either: + - If the configuration is a top-level input, record its digest in + `externalParameters["config"]`. + - Else if there is a known use case for knowing the exact resolved + build configuration, record its digest in `byproducts`. An example use + case might be someone who wishes to parse the configuration to look for + bad patterns, such as `curl | bash`. + - Else omit it. +- `metadata.completeness`: Now implicit from `builder.id`. +- `metadata.reproducible`: Now implicit from `builder.id`. + +## Change history + +### v1.0 + +Major refactor to reduce misinterpretation, including a minor change in model. + +- Significantly expanded all documentation. +- Altered the model slightly to better align with real-world build platforms, + align with reproducible builds, and make verification easier. +- Grouped fields into `buildDefinition` vs `runDetails`. +- Renamed: + - `parameters` -> `externalParameters` (slight change in semantics) + - `environment` -> `internalParameters` (slight change in semantics) + - `materials` -> `resolvedDependencies` (slight change in semantics) + - `buildInvocationId` -> `invocationId` + - `buildStartedOn` -> `startedOn` + - `buildFinishedOn` -> `finishedOn` +- Removed: + - `configSource`: No longer special-cased. Now represented as + `externalParameters` + `resolvedDependencies`. + - `buildConfig`: No longer inlined into the provenance. Can be replaced + with a reference in `externalParameters` or `byproducts`, depending on + the semantics, or omitted if not needed. + - `completeness` and `reproducible`: Now implied by `builder.id`. +- Added: + - ResourceDescriptor: `annotations`, `content`, `downloadLocation`, + `mediaType`, `name` + - Builder: `builderDependencies` and `version` + - `byproducts` +- Changed naming convention for extension fields. + +Differences from RC1 and RC2: + +- Renamed `systemParameters` (RC1 + RC2) -> `internalParameters` (final). +- Changed naming convention for extension fields (in RC2). +- Renamed `localName` (RC1) -> `name` (RC2). +- Added `annotations` and `content` (in RC2). + +### v0.2 + +Refactored to aid clarity and added `buildConfig`. The model is unchanged. + +- Replaced `definedInMaterial` and `entryPoint` with `configSource`. +- Renamed `recipe` to `invocation`. +- Moved `invocation.type` to top-level `buildType`. +- Renamed `arguments` to `parameters`. +- Added `buildConfig`, which can be used as an alternative to `configSource` + to validate the configuration. + +### rename: slsa.dev/provenance + +Renamed to "slsa.dev/provenance". + +### v0.1.1 + +- Added `metadata.buildInvocationId`. + +### v0.1 + +Initial version, named "in-toto.io/Provenance" + +[Statement]: https://github.com/in-toto/attestation/blob/main/spec/v1/statement.md +[in-toto attestation]: https://github.com/in-toto/attestation +[parsing rules]: https://github.com/in-toto/attestation/blob/main/spec/v1/README.md#parsing-rules +[purl]: https://github.com/package-url/purl-spec +[threats]: /spec/v1.0/threats +[trusted]: /spec/v1.0/principles#trust-systems-verify-artifacts diff --git a/docs/spec/v1.1/requirements.md b/docs/spec/v1.1/requirements.md new file mode 100644 index 000000000..23827046f --- /dev/null +++ b/docs/spec/v1.1/requirements.md @@ -0,0 +1,338 @@ +--- +title: Producing artifacts +description: This page covers the detailed technical requirements for producing artifacts at each SLSA level. The intended audience is platform implementers and security engineers. +--- + + +This page covers the detailed technical requirements for producing artifacts at +each SLSA level. The intended audience is platform implementers and security +engineers. + +For an informative description of the levels intended for all audiences, see +[Levels](levels.md). For background, see [Terminology](terminology.md). To +better understand the reasoning behind the requirements, see +[Threats and mitigations](threats.md). + +The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", +"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be +interpreted as described in [RFC 2119](https://www.rfc-editor.org/rfc/rfc2119). + +## Overview + +### Build levels + +In order to produce artifacts with a specific build level, responsibility is +split between the [Producer] and [Build platform]. The build platform MUST +strengthen the security controls in order to achieve a specific level while the +producer MUST choose and adopt a build platform capable of achieving a desired +build level, implementing any controls as specified by the chosen platform. + + + + + + + + + + + +
Implementer + Requirement + Degree + L1L2L3 +
Producer + Choose an appropriate build platform + ✓✓✓ +
Follow a consistent build process + ✓✓✓ +
Distribute provenance + ✓✓✓ +
Build platform + Provenance generation + Exists + ✓✓✓ +
Authentic + ✓✓ +
Unforgeable + ✓ +
Isolation strength + Hosted + ✓✓ +
Isolated + ✓ +
+ +### Security Best Practices + +While the exact definition of what constitutes a secure platform is beyond the +scope of this specification, all implementations MUST use industry security +best practices to be conformant to this specification. This includes, but is +not limited to, using proper access controls, securing communications, +implementing proper management of cryptographic secrets, doing frequent updates, +and promptly fixing known vulnerabilities. + +Various relevant standards and guides can be consulted for that matter such as +the [CIS Critical Security +Controls](https://www.cisecurity.org/controls/cis-controls-list). + +## Producer + +[Producer]: #producer + +A package's producer is the organization that owns and releases the +software. It might be an open-source project, a company, a team within a +company, or even an individual. + +NOTE: There were more requirements for producers in the initial +[draft version (v0.1)](../v0.1/requirements.md#scripted-build) which impacted +how a package can be built. These were removed in the v1.0 specification and +will be reassessed and re-added as indicated in the +[future directions](future-directions.md). + +### Choose an appropriate build platform + +The producer MUST select a build platform that is capable of reaching their +desired SLSA Build Level. + +For example, if a producer wishes to produce a Build Level 3 artifact, they MUST +choose a builder capable of producing Build Level 3 provenance. + +### Follow a consistent build process + +The producer MUST build their artifact in a consistent +manner such that verifiers can form expectations about the build process. In +some implemenatations, the producer MAY provide explicit metadata to a verifier +about their build process. In others, the verifier will form their expectations +implicitly (e.g. trust on first use). + +If a producer wishes to distribute their artifact through a [package ecosystem] +that requires explicit metadata about the build process in the form of a +configuration file, the producer MUST complete the configuration file and keep +it up to date. This metadata might include information related to the artifact's +source repository and build parameters. + +### Distribute provenance + +The producer MUST distribute provenance to artifact consumers. The producer +MAY delegate this responsibility to the +[package ecosystem], provided that the package ecosystem is capable of +distributing provenance. + +## Build Platform + +[Build platform]: #build-platform + +A package's build platform is the infrastructure used to transform the +software from source to package. This includes the transitive closure of all +hardware, software, persons, and organizations that can influence the build. A +build platform is often a hosted, multi-tenant build service, but it could be a +system of multiple independent rebuilders, a special-purpose build platform used +by a single software project, or even an individual's workstation. Ideally, one +build platform is used by many different software packages so that consumers can +[minimize the number of trusted platforms](principles.md). For more background, +see [Build Model](terminology.md#build-model). + +The build platform is responsible for providing two things: [provenance +generation] and [isolation between builds]. The [Build level](levels.md#build-track) describes +the degree to which each of these properties is met. + +### Provenance generation + +[Provenance generation]: #provenance-generation + +The build platform is responsible for generating provenance describing how the +package was produced. + +The SLSA Build level describes the overall provenance integrity according to +minimum requirements on its: + +- *Completeness:* What information is contained in the provenance? +- *Authenticity:* How strongly can the provenance be tied back to the builder? +- *Accuracy:* How resistant is the provenance generation to tampering within + the build process? + + +
RequirementDescriptionL1L2L3 + +
Provenance Exists + +The build process MUST generate provenance that unambiguously identifies the +output package by cryptographic digest and describes how that package was +produced. The format MUST be acceptable to the [package ecosystem] and/or +[consumer](verifying-artifacts.md#consumer). + +It is RECOMMENDED to use the [SLSA Provenance] format and [associated suite] +because it is designed to be interoperable, universal, and unambiguous when +used for SLSA. See that format's documentation for requirements and +implementation guidelines. + +If using an alternate format, it MUST contain the equivalent information as SLSA +Provenance at each level and SHOULD be bi-directionally translatable to SLSA +Provenance. + +- *Completeness:* Best effort. The provenance at L1 SHOULD contain sufficient + information to catch mistakes and simulate the user experience at higher + levels in the absence of tampering. In other words, the contents of the + provenance SHOULD be the same at all Build levels, but a few fields MAY be + absent at L1 if they are prohibitively expensive to implement. +- *Authenticity:* No requirements. +- *Accuracy:* No requirements. + +[SLSA Provenance]: provenance.md +[associated suite]: ../../attestation-model#recommended-suite + +✓✓✓ +
Provenance is Authentic + +*Authenticity:* Consumers MUST be able to validate the authenticity of the +provenance attestation in order to: + +- *Ensure integrity:* Verify that the digital signature of the provenance + attestation is valid and the provenance was not tampered with after the + build. +- *Define trust:* Identify the build platform and other entities that are + necessary to trust in order to trust the artifact they produced. + +This SHOULD be through a digital signature from a private key accessible only +to the build platform component that generated the provenance attestation. + +While many constraints affect choice of signing methodologies, it is +RECOMMENDED that build platforms use signing methodologies which improve the +ability to detect and remediate key compromise, such as methods which rely on +transparency logs or, when transparency isn't appropriate, time stamping +services. + +Authenticity allows the consumer to trust the contents of the provenance +attestation, such as the identity of the build platform. + +*Accuracy:* The provenance MUST be generated by the control plane (i.e. within +the trust boundary [identified in the provenance]) and not by a tenant of the +build platform (i.e. outside the trust boundary), except as noted below. + +- The data in the provenance MUST be obtained from the build platform, either + because the generator *is* the build platform or because the provenance + generator reads the data directly from the build platform. +- The build platform MUST have some security control to prevent tenants from + tampering with the provenance. However, there is no minimum bound on the + strength. The purpose is to deter adversaries who might face legal or + financial risk from evading controls. +- Exceptions for fields that MAY be generated by a tenant of the build platform: + - The names and cryptographic digests of the output artifacts, i.e. + `subject` in [SLSA Provenance]. See [forge output digest of the + provenance](threats#forged-digest) for explanation of why this is + acceptable. + - Any field that is not marked as REQUIRED for Build L2. For example, + `resolvedDependencies` in [SLSA Provenance] MAY be tenant-generated at + Build L2. Builders SHOULD document any such cases of tenant-generated + fields. + +*Completeness:* SHOULD be complete. + +- There MAY be [external parameters] that are not sufficiently captured in + the provenance. +- Completeness of resolved dependencies is best effort. + + ✓✓ +
Provenance is Unforgeable + +*Accuracy:* Provenance MUST be strongly resistant to forgery by tenants. + +- Any secret material used for authenticating the provenance, for example the + signing key used to generate a digital signature, MUST be stored in a secure + management system appropriate for such material and accessible only to the + build service account. +- Such secret material MUST NOT be accessible to the environment running + the user-defined build steps. +- Every field in the provenance MUST be generated or verified by the build + platform in a trusted control plane. The user-controlled build steps MUST + NOT be able to inject or alter the contents, except as noted in [Provenance + is Authentic](#provenance-authentic). (Build L3 does not require additional + fields beyond those of L2.) + +*Completeness:* SHOULD be complete. + +- [External parameters] MUST be fully enumerated. +- Completeness of resolved dependencies is best effort. + +Note: This requirement was called "non-falsifiable" in the initial +[draft version (v0.1)](../v0.1/requirements.md#non-falsifiable). + + ✓ +
+ +### Isolation strength + +[Isolation strength]: #isolation-strength +[Isolation between builds]: #isolation-strength + +The build platform is responsible for isolating between builds, even within the +same tenant project. In other words, how strong of a guarantee do we have that +the build really executed correctly, without external influence? + +The SLSA Build level describes the minimum bar for isolation strength. For more +information on assessing a build platform's isolation strength, see +[Verifying build platforms](verifying-systems.md). + + + + +
RequirementDescriptionL1L2L3 + +
Hosted + + +All build steps ran using a hosted build platform on shared or dedicated +infrastructure, not on an individual's workstation. + +Examples: GitHub Actions, Google Cloud Build, Travis CI. + + ✓✓ +
Isolated + + +The build platform ensured that the build steps ran in an isolated environment, +free of unintended external influence. In other words, any external influence on +the build was specifically requested by the build itself. This MUST hold true +even between builds within the same tenant project. + +The build platform MUST guarantee the following: + +- It MUST NOT be possible for a build to access any secrets of the build + platform, such as the provenance signing key, because doing so would + compromise the authenticity of the provenance. +- It MUST NOT be possible for two builds that overlap in time to influence one + another, such as by altering the memory of a different build process running + on the same machine. +- It MUST NOT be possible for one build to persist or influence the build + environment of a subsequent build. In other words, an ephemeral build + environment MUST be provisioned for each build. +- It MUST NOT be possible for one build to inject false entries into a build + cache used by another build, also known as "cache poisoning". In other + words, the output of the build MUST be identical whether or not the cache is + used. +- The build platform MUST NOT open services that allow for remote influence + unless all such interactions are captured as `externalParameters` in the + provenance. + +There are no sub-requirements on the build itself. Build L3 is limited to +ensuring that a well-intentioned build runs securely. It does not require that +a build platform prevents a producer from performing a risky or insecure build. In +particular, the "Isolated" requirement does not prohibit a build from calling +out to a remote execution service or a "self-hosted runner" that is outside the +trust boundary of the build platform. + +NOTE: This requirement was split into "Isolated" and "Ephemeral Environment" +in the initial [draft version (v0.1)](../v0.1/requirements.md). + +NOTE: This requirement is not to be confused with "Hermetic", which roughly +means that the build ran with no network access. Such a requirement requires +substantial changes to both the build platform and each individual build, and is +considered in the [future directions](future-directions.md). + + ✓ +
+ +[external parameters]: provenance.md#externalParameters +[identified in the provenance]: provenance.md#model +[package ecosystem]: verifying-artifacts.md#package-ecosystem diff --git a/docs/spec/v1.1/schema/provenance.cue b/docs/spec/v1.1/schema/provenance.cue new file mode 100644 index 000000000..c4e308628 --- /dev/null +++ b/docs/spec/v1.1/schema/provenance.cue @@ -0,0 +1,46 @@ +{ + // Standard attestation fields: + "_type": "https://in-toto.io/Statement/v1", + "subject": [...], + + // Predicate: + "predicateType": "https://slsa.dev/provenance/v1", + "predicate": { + "buildDefinition": { + "buildType": string, + "externalParameters": object, + "internalParameters": object, + "resolvedDependencies": [ ...#ResourceDescriptor ], + }, + "runDetails": { + "builder": { + "id": string, + "builderDependencies": [ ...#ResourceDescriptor ], + "version": { ...string }, + }, + "metadata": { + "invocationId": string, + "startedOn": #Timestamp, + "finishedOn": #Timestamp, + }, + "byproducts": [ ...#ResourceDescriptor ], + } + } +} + +#ResourceDescriptor: { + "uri": string, + "digest": { + "sha256": string, + "sha512": string, + "gitCommit": string, + [string]: string, + }, + "name": string, + "downloadLocation": string, + "mediaType": string, + "content": bytes, // base64-encoded + "annotations": object, +} + +#Timestamp: string // --
T::Z diff --git a/docs/spec/v1.1/schema/provenance.proto b/docs/spec/v1.1/schema/provenance.proto new file mode 100644 index 000000000..231702598 --- /dev/null +++ b/docs/spec/v1.1/schema/provenance.proto @@ -0,0 +1,50 @@ +syntax = "proto3"; + +package slsa.v1; + +import "google/protobuf/struct.proto"; +import "google/protobuf/timestamp.proto"; + +// NOTE: While file uses snake_case as per the Protocol Buffers Style Guide, the +// provenance is always serialized using JSON with lowerCamelCase. Protobuf +// tooling performs this case conversion automatically. + +message Provenance { + BuildDefinition build_definition = 1; + RunDetails run_details = 2; +} + +message BuildDefinition { + string build_type = 1; + google.protobuf.Struct external_parameters = 2; + google.protobuf.Struct internal_parameters = 3; + repeated ResourceDescriptor resolved_dependencies = 4; +} + +message ResourceDescriptor { + string uri = 1; + map digest = 2; + string name = 3; + string download_location = 4; + string media_type = 5; + bytes content = 6; + google.protobuf.Struct annotations = 7; +} + +message RunDetails { + Builder builder = 1; + BuildMetadata metadata = 2; + repeated ResourceDescriptor byproducts = 3; +} + +message Builder { + string id = 1; + map version = 2; + repeated ResourceDescriptor builder_dependencies = 3; +} + +message BuildMetadata { + string invocation_id = 1; + google.protobuf.Timestamp started_on = 2; + google.protobuf.Timestamp finished_on = 3; +} diff --git a/docs/spec/v1.1/terminology.md b/docs/spec/v1.1/terminology.md new file mode 100644 index 000000000..0ddfa76e3 --- /dev/null +++ b/docs/spec/v1.1/terminology.md @@ -0,0 +1,339 @@ +--- +title: Terminology +description: Before diving into the SLSA specification levels, we need to establish a core set of terminology and models to describe what we're protecting. +--- + + +Before diving into the [SLSA Levels](levels.md), we need to establish a core set +of terminology and models to describe what we're protecting. + +## Software supply chain + +SLSA's framework addresses every step of the software supply chain - the +sequence of steps resulting in the creation of an artifact. We represent a +supply chain as a [directed acyclic graph] of sources, builds, dependencies, and +packages. One artifact's supply chain is a combination of its dependencies' +supply chains plus its own sources and builds. + +[directed acyclic graph]: https://en.wikipedia.org/wiki/Directed_acyclic_graph + +![Software Supply Chain Model](images/supply-chain-model.svg) + +| Term | Description | Example | +| --- | --- | --- | +| Artifact | An immutable blob of data; primarily refers to software, but SLSA can be used for any artifact. | A file, a git commit, a directory of files (serialized in some way), a container image, a firmware image. | +| Attestation | An authenticated statement (metadata) about a software artifact or collection of software artifacts. | A signed [SLSA Provenance] file. | +| Source | Artifact that was directly authored or reviewed by persons, without modification. It is the beginning of the supply chain; we do not trace the provenance back any further. | Git commit (source) hosted on GitHub (platform). | +| [Build] | Process that transforms a set of input artifacts into a set of output artifacts. The inputs may be sources, dependencies, or ephemeral build outputs. | .travis.yml (process) run by Travis CI (platform). | +| [Package] | Artifact that is "published" for use by others. In the model, it is always the output of a build process, though that build process can be a no-op. | Docker image (package) distributed on DockerHub (platform). A ZIP file containing source code is a package, not a source, because it is built from some other source, such as a git commit. | +| Dependency | Artifact that is an input to a build process but that is not a source. In the model, it is always a package. | Alpine package (package) distributed on Alpine Linux (platform). | + +[build]: #build-model +[package]: #package-model +[SLSA Provenance]: /provenance/v1 + +### Roles + +Throughout the specification, you will see reference to the following roles +that take part in the software supply chain. Note that in practice a role may +be filled by more than one person or an organization. Similarly, a person or +organization may act as more than one role in a particular software supply +chain. + +| Role | Description | Examples +| --- | --- | --- +| Producer | A party who creates software and provides it to others. Producers are often also consumers. | An open source project's maintainers. A software vendor. +| Verifier | A party who inspect an artifact's provenance to determine the artifact's authenticity. | A business's software ingestion system. A programming language ecosystem's package registry. +| Consumer | A party who uses software provided by a producer. The consumer may verify provenance for software they consume or delegate that responsibility to a separate verifier. | A developer who uses open source software distributions. A business that uses a point of sale system. +| Infrastructure provider | A party who provides software or services to other roles. | A package registry's maintainers. A build platform's maintainers. + +### Build model + +

Model Build

+ +We model a build as running on a multi-tenant *build platform*, where each +execution is independent. + +1. A tenant invokes the build by specifying *external parameters* through an + *interface*, either directly or via some trigger. Usually, at least one of + these external parameters is a reference to a *dependency*. (External + parameters are literal values while dependencies are artifacts.) +2. The build platform's *control plane* interprets these external parameters, + fetches an initial set of dependencies, initializes a *build environment*, + and then starts the execution within that environment. +3. The build then performs arbitrary steps, which might include fetching + additional dependencies, and then produces one or more *output* artifacts. + The steps within the build environment are under the tenant's control. + The build platform isolates build environments from one another to some + degree (which is measured by the SLSA Build Level). +4. Finally, for SLSA Build L2+, the control plane outputs *provenance* + describing this whole process. + +Notably, there is no formal notion of "source" in the build model, just external +parameters and dependencies. Most build platforms have an explicit "source" +artifact to build from, which is often a git repository; in the build model, the +reference to this artifact is an external parameter while the artifact itself is +a dependency. + +For examples of how this model applies to real-world build platforms, see [index +of build types](/provenance/v1#index-of-build-types). + +| Primary Term | Description +| --- | --- +| Platform | System that allows tenants to run builds. Technically, it is the transitive closure of software and services that must be trusted to faithfully execute the build. It includes software, hardware, people, and organizations. +| Admin | A privileged user with administrative access to the platform, potentially allowing them to tamper with builds or the control plane. +| Tenant | An untrusted user that builds an artifact on the platform. The tenant defines the build steps and external parameters. +| Control plane | Build platform component that orchestrates each independent build execution and produces provenance. The control plane is managed by an admin and trusted to be outside the tenant's control. +| Build | Process that converts input sources and dependencies into output artifacts, defined by the tenant and executed within a single build environment on a platform. +| Steps | The set of actions that comprise a build, defined by the tenant. +| Build environment | The independent execution context in which the build runs, initialized by the control plane. In the case of a distributed build, this is the collection of all such machines/containers/VMs that run steps. +| Build caches | An intermediate artifact storage managed by the platform that maps intermediate artifacts to their explicit inputs. A build may share build caches with any subsequent build running on the platform. +| External parameters | The set of top-level, independent inputs to the build, specified by a tenant and used by the control plane to initialize the build. +| Dependencies | Artifacts fetched during initialization or execution of the build process, such as configuration files, source artifacts, or build tools. +| Outputs | Collection of artifacts produced by the build. +| Provenance | Attestation (metadata) describing how the outputs were produced, including identification of the platform and external parameters. + +
Ambiguous terms to avoid + +- *Build recipe:* Could mean *external parameters,* but may include concrete + steps of how to perform a build. To avoid implementation details, we don't + define this term, but always use "external parameters" which is the + interface to a build platform. Similar terms are *build configuration + source* and *build definition*. +- *Builder:* Usually means *build platform*, but might be used for *build + environment*, the user who invoked the build, or a build tool from + *dependencies*. To avoid confusion, we always use "build platform". The only + exception is in the [provenance](/provenance/v1), where `builder` is used as + a more concise field name. + +
+ +### Package model + +Software is distributed in identifiable units called packages +according the rules and conventions of a package ecosystem. +Examples of formal ecosystems include [Python/PyPA](https://www.pypa.io), +[Debian/Apt](https://wiki.debian.org/DebianRepository/Format), and +[OCI](https://github.com/opencontainers/distribution-spec), while examples of +informal ecosystems include links to files on a website or distribution of +first-party software within a company. + +Abstractly, a consumer locates software within an ecosystem by asking a +package registry to resolve a mutable package name into an +immutable package artifact.[^label] To publish a package +artifact, the software producer asks the registry to update this mapping to +resolve to the new artifact. The registry represents the entity or entities with +the power to alter what artifacts are accepted by consumers for a given package +name. For example, if consumers only accept packages signed by a particular +public key, then it is access to that public key that serves as the registry. + +The package name is the primary security boundary within a package ecosystem. +Different package names represent materially different pieces of +software---different owners, behaviors, security properties, and so on. +Therefore, **the package name is the primary unit being protected in SLSA**. +It is the primary identifier to which consumers attach expectations. + +[^label]: This resolution might include a version number, label, or some other + selector in addition to the package name, but that is not important to SLSA. + +| Term | Description | +| ---- | ----------- | +| Package | An identifiable unit of software intended for distribution, ambiguously meaning either an "artifact" or a "package name". Only use this term when the ambiguity is acceptable or desirable. | +| Package artifact | A file or other immutable object that is intended for distribution. | +| Package ecosystem | A set of rules and conventions governing how packages are distributed, including how clients resolve a package name into one or more specific artifacts. | +| Package manager client | Client-side tooling to interact with a package ecosystem. | +| Package name |

The primary identifier for a mutable collection of artifacts that all represent different versions of the same software. This is the primary identifier that consumers use to obtain the software.

A package name is specific to an ecosystem + registry, has a maintainer, is more general than a specific hash or version, and has a "correct" source location. A package ecosystem may group package names into some sort of hierarchy, such as the Group ID in Maven, though SLSA does not have a special term for this. | +| Package registry | An entity responsible for mapping package names to artifacts within a packaging ecosystem. Most ecosystems support multiple registries, usually a single global registry and multiple private registries. | +| Publish [a package] | Make an artifact available for use by registering it with the package registry. In technical terms, this means associating an artifact to a package name. This does not necessarily mean making the artifact fully public; an artifact may be published for only a subset of users, such as internal testing or a closed beta. | + +

Ambiguous terms to avoid + +- *Package repository:* Could mean either package registry or package name, + depending on the ecosystem. To avoid confusion, we always use "repository" + exclusively to mean "source repository", where there is no ambiguity. +- *Package manager* (without "client"): Could mean either package ecosystem, + package registry, or client-side tooling. + +
+ +### Mapping to real-world ecosystems + +Most real-world ecosystems fit the package model above but use different terms. +The table below attempts to document how various ecosystems map to the SLSA +Package model. There are likely mistakes and omissions; corrections and +additions are welcome! + + + + + + + + + + + + + + + + + + + + + + + + + + +
Package ecosystem + Package registry + Package name + Package artifact +
Languages +
Cargo (Rust) + Registry + Crate name + Artifact +
CPAN (Perl) + Upload server + Distribution + Release (or Distribution) +
Go + Module proxy + Module path + Module +
Maven (Java) + Repository + Group ID + Artifact ID + Artifact +
npm (JavaScript) + Registry + Package Name + Package +
NuGet (C#) + Host + Project + Package +
PyPA (Python) + Index + Project Name + Distribution +
Operating systems +
Dpkg (e.g. Debian) + ? + Package name + Package +
Flatpak + Repository + Application + Bundle +
Homebrew (e.g. Mac) + Repository (Tap) + Package name (Formula) + Binary package (Bottle) +
Pacman (e.g. Arch) + Repository + Package name + Package +
RPM (e.g. Red Hat) + Repository + Package name + Package +
nix (e.g. NixOS) + ? + Store Object? + Package or Derivation +
Storage systems +
GCS + n/a + Object name + Object +
OCI/Docker + Registry + Repository + Object +
Meta +
deps.dev: System + Packaging authority + Package + n/a +
purl: type + Namespace + Name + n/a +
+ +Notes: + +- Go uses a significantly different distribution model than other ecosystems. + In go, the package name is a source repository URL. While clients can fetch + directly from that URL---in which case there is no "package" or + "registry"---they usually fetch a zip file from a *module proxy*. The module + proxy acts as both a builder (by constructing the package artifact from + source) and a registry (by mapping package name to package artifact). People + trust the module proxy because builds are independently reproducible and a + *checksum database* guarantees that all clients receive the same artifact + for a given URL. + +### Verification model + +Verification in SLSA is performed in two ways. Firstly, the build platform is +certified to ensure conformance with the requirements at the level claimed by +the build platform. This certification should happen on a recurring cadence with +the outcomes published by the platform operator for their users to review and +make informed decisions about which builders to trust. + +Secondly, artifacts are verified to ensure they meet the producer defined +expectations of where the package source code was retrieved from and on what +build platform the package was built. + +![Verification Model](images/verification-model.svg) + +| Term | Description | +|--------------|---- | +| Expectations | A set of constraints on the package's provenance metadata. The package producer sets expectations for a package, whether explicitly or implicitly. | +| Provenance verification | Artifacts are verified by the package ecosystem to ensure that the package's expectations are met before the package is used. | +| Build platform certification | [Build platforms are certified](verifying-systems.md) for their conformance to the SLSA requirements at the stated level. | + +The examples below suggest some ways that expectations and verification may be +implemented for different, broadly defined, package ecosystems. + +
Example: Small software team + +| Term | Example | +| ---- | ------- | +| Expectations | Defined by the producer's security personnel and stored in a database. | +| Provenance verification | Performed automatically on cluster nodes before execution by querying the expectations database. | +| Build platform certification | The build platform implementer follows secure design and development best practices, does annual penetration testing exercises, and self-certifies their conformance to SLSA requirements. | + +
+ +
Example: Open source language distribution + +| Term | Example | +| ---- | ------- | +| Expectations | Defined separately for each package and stored in the package registry. | +| Provenance verification | The language distribution registry verifies newly uploaded packages meet expectations before publishing them. Further, the package manager client also verifies expectations prior to installing packages. | +| Build platform certification | Performed by the language ecosystem packaging authority. | + +
diff --git a/docs/spec/v1.1/threats-overview.md b/docs/spec/v1.1/threats-overview.md new file mode 100644 index 000000000..e06cab75e --- /dev/null +++ b/docs/spec/v1.1/threats-overview.md @@ -0,0 +1,110 @@ +--- +title: Supply chain threats +description: Attacks can occur at every link in a typical software supply chain, and these kinds of attacks are increasingly public, disruptive, and costly in today's environment. This page is an introduction to possible attacks throughout the supply chain and how SLSA can help. +--- + +Attacks can occur at every link in a typical software supply chain, and these +kinds of attacks are increasingly public, disruptive, and costly in today's +environment. + +This page is an introduction to possible attacks throughout the supply chain and how +SLSA can help. For a more technical discussion, see [Threats & mitigations](threats.md). + +## Summary + +![Supply Chain Threats](images/supply-chain-threats.svg) + +See [Terminology](terminology.md) for an explanation of the supply chain +model. + +SLSA's primary focus is supply chain integrity, with a secondary focus on +availability. Integrity means protection against tampering or unauthorized +modification at any stage of the software lifecycle. Within SLSA, we divide +integrity into source integrity vs build integrity. + +**Source integrity:** Ensure that all changes to the source code reflect the +intent of the software producer. Intent of an organization is difficult to +define, so SLSA approximates this as approval from two authorized +representatives. + +**Build integrity:** Ensure that the package is built from the correct, +unmodified sources and dependencies according to the build recipe defined by the +software producer, and that artifacts are not modified as they pass between +development stages. + +**Availability:** Ensure that the package can continue to be built and +maintained in the future, and that all code and change history is available for +investigations and incident response. + +### Real-world examples + +Many recent high-profile attacks were consequences of supply chain integrity vulnerabilities, and could have been prevented by SLSA's framework. For example: + + + + + + + + + + + + + +
+Integrity threat +Known example +How SLSA can help +
A +Submit unauthorized change (to source repo) +SushiSwap: Contractor with repository access pushed a malicious commit redirecting cryptocurrency to themself. +Two-person review could have caught the unauthorized change. +
B +Compromise source repo +PHP: Attacker compromised PHP's self-hosted git server and injected two malicious commits. +A better-protected source code platform would have been a much harder target for the attackers. +
C +Build from modified source (not matching source repo) +Webmin: Attacker modified the build infrastructure to use source files not matching source control. +A SLSA-compliant build server would have produced provenance identifying the actual sources used, allowing consumers to detect such tampering. +
D +Use compromised dependency (i.e. A-H, recursively) +event-stream: Attacker added an innocuous dependency and then later updated the dependency to add malicious behavior. The update did not match the code submitted to GitHub (i.e. attack F). +Applying SLSA recursively to all dependencies would have prevented this particular vector, because the provenance would have indicated that it either wasn't built from a proper builder or that the source did not come from GitHub. +
E +Compromise build process +SolarWinds: Attacker compromised the build platform and installed an implant that injected malicious behavior during each build. +Higher SLSA levels require stronger security controls for the build platform, making it more difficult to compromise and gain persistence. +
F +Upload modified package (not matching build process) +CodeCov: Attacker used leaked credentials to upload a malicious artifact to a GCS bucket, from which users download directly. +Provenance of the artifact in the GCS bucket would have shown that the artifact was not built in the expected manner from the expected source repo. +
G +Compromise package repo +Attacks on Package Mirrors: Researcher ran mirrors for several popular package repositories, which could have been used to serve malicious packages. +Similar to above (F), provenance of the malicious artifacts would have shown that they were not built as expected or from the expected source repo. +
H +Use compromised package +Browserify typosquatting: Attacker uploaded a malicious package with a similar name as the original. +SLSA does not directly address this threat, but provenance linking back to source control can enable and enhance other solutions. +
+ + + + + + +
+Availability threat +Known example +How SLSA can help +
D +Dependency becomes unavailable +Mimemagic: Producer intentionally removes package or version of package from repository with no warning. Network errors or service outages may also make packages unavailable temporarily. +SLSA does not directly address this threat. +
+ +A SLSA level helps give consumers confidence that software has not been tampered +with and can be securely traced back to source—something that is difficult, if +not impossible, to do with most software today. diff --git a/docs/spec/v1.1/threats.md b/docs/spec/v1.1/threats.md new file mode 100644 index 000000000..0e6e7f6a1 --- /dev/null +++ b/docs/spec/v1.1/threats.md @@ -0,0 +1,524 @@ +--- +title: Threats & mitigations +description: A comprehensive technical analysis of supply chain threats and their corresponding mitigations in SLSA. +--- + +What follows is a comprehensive technical analysis of supply chain threats and +their corresponding mitigations in SLSA. For an introduction to the +supply chain threats that SLSA protects agains, see [Supply chain threats]. + +The examples on this page are meant to: + +- Explain the reasons for each of the SLSA [requirements](requirements.md). +- Increase confidence that the SLSA requirements are sufficient to achieve the + desired [level](levels.md) of integrity protection. +- Help implementers better understand what they are protecting against so that + they can better design and implement controls. + +
+ +![Supply Chain Threats](images/supply-chain-threats.svg) + +See [Terminology](terminology.md) for an explanation of supply chain model. + +## Source threats + +A source integrity threat is a potential for an adversary to introduce a change +to the source code that does not reflect the intent of the software producer. +This includes the threat of an authorized individual introducing an unauthorized +change---in other words, an insider threat. + +SLSA v1.0 does not address source threats, but we anticipate doing so in a +[future version](future-directions.md#source-track). In the meantime, the +threats and potential mitigations listed here show how SLSA v1.0 can fit into a +broader supply chain security program. + +### (A) Submit unauthorized change + +An adversary introduces a change through the official source control management +interface without any special administrator privileges. + +SLSA v1.0 does not address this threat, but it may be addressed in a [future +version](future-directions.md). + +### (B) Compromise source repo + +An adversary introduces a change to the source control repository through an +administrative interface, or through a compromise of the underlying +infrastructure. + +SLSA v1.0 does not address this threat, but it may be addressed in a [future +version](future-directions.md). + +### (C) Build from modified source + +An adversary builds from a version of the source code that does not match the +official source control repository. + +The mitigation here is to compare the provenance against expectations for the +package, which depends on SLSA Build L1 for provenance. (Threats against the +provenance itself are covered by (E) and (F).) + +
Build from unofficial fork of code (expectations) + +*Threat:* Build using the expected CI/CD process but from an unofficial fork of +the code that may contain unauthorized changes. + +*Mitigation:* Verifier requires the provenance's source location to match an +expected value. + +*Example:* MyPackage is supposed to be built from GitHub repo `good/my-package`. +Instead, it is built from `evilfork/my-package`. Solution: Verifier rejects +because the source location does not match. + +
+
Build from unofficial branch or tag (expectations) + +*Threat:* Build using the expected CI/CD process and source location, but +checking out an "experimental" branch or similar that may contain code not +intended for release. + +*Mitigation:* Verifier requires that the provenance's source branch/tag matches +an expected value, or that the source revision is reachable from an expected +branch. + +*Example:* MyPackage's releases are tagged from the `main` branch, which has +branch protections. Adversary builds from the unprotected `experimental` branch +containing unofficial changes. Solution: Verifier rejects because the source +revision is not reachable from `main`. + +
+
Build from unofficial build steps (expectations) + +*Threat:* Build the package using the proper CI/CD platform but with unofficial +build steps. + +*Mitigation:* Verifier requires that the provenance's build configuration source +matches an expected value. + +*Example:* MyPackage is expected to be built by Google Cloud Build using the +build steps defined in the source's `cloudbuild.yaml` file. Adversary builds +with Google Cloud Build, but using custom build steps provided over RPC. +Solution: Verifier rejects because the build steps did not come from the +expected source. + +
+
Build from unofficial parameters (expectations) + +*Threat:* Build using the expected CI/CD process, source location, and +branch/tag, but using a parameter that injects unofficial behavior. + +*Mitigation:* Verifier requires that the provenance's external parameters all +match expected values. + +*Example 1:* MyPackage is supposed to be built from the `release.yml` workflow. +Adversary builds from the `debug.yml` workflow. Solution: Verifier rejects +because the workflow parameter does not match the expected value. + +*Example 2:* MyPackage's GitHub Actions Workflow uses `github.event.inputs` to +allow users to specify custom compiler flags per invocation. Adversary sets a +compiler flag that overrides a macro to inject malicious behavior into the +output binary. Solution: Verifier rejects because the `inputs` parameter was not +expected. + +
+
Build from modified version of code modified after checkout (expectations) + +*Threat:* Build from a version of the code that includes modifications after +checkout. + +*Mitigation:* Build platform pulls directly from the source repository and +accurately records the source location in provenance. + +*Example:* Adversary fetches from MyPackage's source repo, makes a local commit, +then requests a build from that local commit. Builder records the fact that it +did not pull from the official source repo. Solution: Verifier rejects because +the source repo does not match the expected value. + +
+ +## Dependency threats + +A dependency threat is a vector for an adversary to introduce behavior to an +artifact through external software that the artifact requires to function. + +SLSA mitigates dependency threats when you verify your dependencies' SLSA +provenance. + +### (D) Use compromised dependency + +
Use a compromised build dependency + +*Threat:* The adversary injects malicious code into software required to build +the artifact. + +*Mitigation:* N/A - This threat is out of scope of SLSA v1.0, though the build +provenance may list build dependencies on a best-effort basis for forensic +analysis. You may be able to mitigate this threat by pinning your build +dependencies, preferably by digest rather than version number. Alternatively, +you can [apply SLSA recursively](verifying-artifacts.md#step-3-optional-check-dependencies-recursively), +but we have not yet standardized how to do so. + +*Example:* The artifact uses `libFoo` and requires its source code to compile. +The adversary compromises `libFoo`'s source repository and inserts malicious +code. When your artifact builds, it contains the adversary's malicious code. + +
+ +
Use a compromised runtime dependency + +*Threat:* The adversary injects malicious code into software required to run the +artifact. + +*Mitigation:* N/A - This threat is out of scope of SLSA v1.0. However, you can +mitigate this threat by verifying SLSA provenance for all of your runtime +dependencies that provide provenance. + +*Example:* The artifact dynamically links `libBar` and requires a binary version +to run. The adversary compromises `libBar`'s build process and inserts malicious +code. When your artifact runs, it contains the adversary's malicious code. + +
+ +## Build threats + +A build integrity threat is a potential for an adversary to introduce behavior +to an artifact without changing its source code, or to build from a +source, dependency, and/or process that is not intended by the software +producer. + +The SLSA Build track mitigates these threats when the consumer +[verifies artifacts](verifying-artifacts.md) against expectations, confirming +that the artifact they recieved was built in the expected manner. + +### (E) Compromise build process + +An adversary introduces an unauthorized change to a build output through +tampering of the build process; or introduces false information into the +provenance. + +These threats are directly addressed by the SLSA Build track. + +
Forge values of the provenance (other than output digest) (Build L2+) + +*Threat:* Generate false provenance and get the trusted control plane to sign +it. + +*Mitigation:* At Build L2+, the trusted control plane [generates][authentic] all +information that goes in the provenance, except (optionally) the output artifact +hash. At Build L3+, this is [hardened][unforgeable] to prevent compromise even +by determined adversaries. + +*Example 1 (Build L2):* Provenance is generated on the build worker, which the +adversary has control over. Adversary uses a malicious process to get the build +platform to claim that it was built from source repo `good/my-package` when it +was really built from `evil/my-package`. Solution: Builder generates and signs +the provenance in the trusted control plane; the worker reports the output +artifacts but otherwise has no influence over the provenance. + +*Example 2 (Build L3):* Provenance is generated in the trusted control plane, +but workers can break out of the container to access the signing material. +Solution: Builder is hardened to provide strong isolation against tenant +projects. + +
+
Forge output digest of the provenance (n/a) + +*Threat:* The tenant-controlled build process sets output artifact digest +(`subject` in SLSA Provenance) without the trusted control plane verifying that +such an artifact was actually produced. + +*Mitigation:* None; this is not a problem. Any build claiming to produce a given +artifact could have actually produced it by copying it verbatim from input to +output.[^preimage] (Reminder: Provenance is only a claim that a particular +artifact was *built*, not that it was *published* to a particular registry.) + +*Example:* A legitimate MyPackage artifact has digest `abcdef` and is built +from source repo `good/my-package`. A malicious build from source repo +`evil/my-package` claims that it built artifact `abcdef` when it did not. +Solution: Verifier rejects because the source location does not match; the +forged digest is irrelevant. + +[^preimage]: Technically this requires the artifact to be known to the + adversary. If they only know the digest but not the actual contents, they + cannot actually build the artifact without a [preimage attack] on the digest + algorithm. However, even still there are no known concerns where this is a + problem. + +[preimage attack]: https://en.wikipedia.org/wiki/Preimage_attack + +
+
Compromise project owner (Build L2+) + +*Threat:* An adversary gains owner permissions for the artifact's build project. + +*Mitigation:* The build project owner must not have the ability to influence the +build process or provenance generation. + +*Example:* MyPackage is built on Awesome Builder under the project "mypackage". +Adversary is an administrator of the "mypackage" project. Awesome Builder allows +administrators to debug build machines via SSH. An adversary uses this feature +to alter a build in progress. + +
+
Compromise other build (Build L3) + +*Threat:* Perform a malicious build that alters the behavior of a benign +build running in parallel or subsequent environments. + +*Mitigation:* Builds are [isolated] from one another, with no way for one to +affect the other or persist changes. + +*Example 1:* A build platform runs all builds for project MyPackage on +the same machine as the same Linux user. An adversary starts a malicious build +that listens for another build and swaps out source files, then starts a benign +build. The benign build uses the malicious build's source files, but its +provenance says it used benign source files. Solution: The build platform +changes architecture to isolate each build in a separate VM or similar. + +*Example 2:* A build platform uses the same machine for subsequent +builds. An adversary first runs a build that replaces the `make` binary with a +malicious version, then subsequently runs an otherwise benign build. Solution: +The builder changes architecture to start each build with a clean machine image. + +
+
Steal cryptographic secrets (Build L3) + +*Threat:* Use or exfiltrate the provenance signing key or some other +cryptographic secret that should only be available to the build platform. + +*Mitigation:* Builds are [isolated] from the trusted build platform control +plane, and only the control plane has [access][unforgeable] to cryptographic +secrets. + +*Example:* Provenance is signed on the build worker, which the adversary has +control over. Adversary uses a malicious process that generates false provenance +and signs it using the provenance signing key. Solution: Builder generates and +signs provenance in the trusted control plane; the worker has no access to the +key. + +
+
Poison the build cache (Build L3) + +*Threat:* Add a malicious artifact to a build cache that is later picked up by a +benign build process. + +*Mitigation:* Build caches must be [isolate][isolated] between builds to prevent +such cache poisoning attacks. + +*Example:* Build platform uses a build cache across builds, keyed by the hash of +the source file. Adversary runs a malicious build that creates a "poisoned" +cache entry with a falsified key, meaning that the value wasn't really produced +from that source. A subsequent build then picks up that poisoned cache entry. + +
+
Compromise build platform admin (verification) + +*Threat:* An adversary gains admin permissions for the artifact's build platform. + +*Mitigation:* The build platform must have controls in place to prevent and +detect abusive behavior from administrators (e.g. two-person approvals, audit +logging). + +*Example:* MyPackage is built on Awesome Builder. Awesome Builder allows +engineers on-call to SSH into build machines to debug production issues. An +adversary uses this access to modify a build in progress. Solution: Consumers +do not accept provenance from the build platform unless they trust sufficient +controls are in place to prevent abusing admin privileges. + +
+ +### (F) Upload modified package + +An adversary uploads a package not built from the proper build process. + +
Build with untrusted CI/CD (expectations) + +*Threat:* Build using an unofficial CI/CD pipeline that does not build in the +correct way. + +*Mitigation:* Verifier requires provenance showing that the builder matched an +expected value. + +*Example:* MyPackage is expected to be built on Google Cloud Build, which is +trusted up to Build L3. Adversary builds on SomeOtherBuildPlatform, which is only +trusted up to Build L2, and then exploits SomeOtherBuildPlatform to inject +malicious behavior. Solution: Verifier rejects because builder is not as +expected. + +
+
Upload package without provenance (Build L1) + +*Threat:* Upload a package without provenance. + +*Mitigation:* Verifier requires provenance before accepting the package. + +*Example:* Adversary uploads a malicious version of MyPackage to the package +repository without provenance. Solution: Verifier rejects because provenance is +missing. + +
+
Tamper with artifact after CI/CD (Build L1) + +*Threat:* Take a benign version of the package, modify it in some way, then +re-upload it using the original provenance. + +*Mitigation:* Verifier checks that the provenance's `subject` matches the hash +of the package. + +*Example:* Adversary performs a proper build, modifies the artifact, then +uploads the modified version of the package to the repository along with the +provenance. Solution: Verifier rejects because the hash of the artifact does not +match the `subject` found within the provenance. + +
+
Tamper with provenance (Build L2) + +*Threat:* Perform a build that would not meet expectations, then modify the +provenance to make the expectations checks pass. + +*Mitigation:* Verifier only accepts provenance with a valid [cryptographic +signature][authentic] or equivalent proving that the provenance came from an +acceptable builder. + +*Example:* MyPackage is expected to be built by GitHub Actions from the +`good/my-package` repo. Adversary builds with GitHub Actions from the +`evil/my-package` repo and then modifies the provenance so that the source looks +like it came from `good/my-package`. Solution: Verifier rejects because the +cryptographic signature is no longer valid. + +
+ +### (G) Compromise package repo + +An adversary modifies the package on the package repository using an +administrative interface or through a compromise of the infrastructure. + +
De-list artifact + +*Threat:* The package repository stops serving the artifact. + +*Mitigation:* N/A - This threat is out of scope of SLSA v1.0. + +
+ +
De-list provenance + +*Threat:* The package repository stops serving the provenance. + +*Mitigation:* N/A - This threat is out of scope of SLSA v1.0. + +
+ +### (H) Use compromised package + +An adversary modifies the package after it has left the package repository, or +tricks the user into using an unintended package. + +
Typosquatting + +*Threat:* Register a package name that is similar looking to a popular package +and get users to use your malicious package instead of the benign one. + +*Mitigation:* **Mostly outside the scope of SLSA.** That said, the requirement +to make the source available can be a mild deterrent, can aid investigation or +ad-hoc analysis, and can complement source-based typosquatting solutions. + +
+ +## Availability threats + +An availability threat is a potential for an adversary to deny someone from +reading a source and its associated change history, or from building a package. + +SLSA v1.0 does not address availability threats, though future versions might. + +
(A)(B) Delete the code + +*Threat:* Perform a build from a particular source revision and then delete that +revision or cause it to get garbage collected, preventing anyone from inspecting +the code. + +*Mitigation:* Some system retains the revision and its version control history, +making it available for inspection indefinitely. Users cannot delete the +revision except as part of a transparent legal or privacy process. + +*Example:* An adversary submits malicious code to the MyPackage GitHub repo, +builds from that revision, then does a force push to erase that revision from +history (or requests that GitHub delete the repo.) This would make the revision +unavailable for inspection. Solution: Verifier rejects the package because it +lacks a positive attestation showing that some system, such as GitHub, ensured +retention and availability of the source code. + +
+
(D) A dependency becomes temporarily or permanently unavailable to the build process + +*Threat:* Unable to perform a build with the intended dependencies. + +*Mitigation:* **Outside the scope of SLSA.** That said, some solutions to +support hermetic and reproducible builds may also reduce the impact of this +threat. + +
+ +## Verification threats + +Threats that can compromise the ability to prevent or detect the supply chain +security threats above. + +
Tamper with recorded expectations + +*Threat:* Modify the verifier's recorded expectations, causing the verifier to +accept an unofficial package artifact. + +*Mitigation:* Changes to recorded expectations requires some form of +authorization, such as two-party review. + +*Example:* The package ecosystem records its expectations for a given package +name in a configuration file that is modifiable by that package's producer. The +configuration for MyPackage expects the source repository to be +`good/my-package`. The adversary modifies the configuration to also accept +`evil/my-package`, and then builds from that repository and uploads a malicious +version of the package. Solution: Changes to the recorded expectations require +two-party review. + +
+
Forge change metadata + +*Threat:* Forge the change metadata to alter attribution, timestamp, or +discoverability of a change. + +*Mitigation:* Source control platform strongly authenticates actor identity, +timestamp, and parent revisions. + +*Example:* Adversary submits a git commit with a falsified author and timestamp, +and then rewrites history with a non-fast-forward update to make it appear to +have been made long ago. Solution: Consumer detects this by seeing that such +changes are not strongly authenticated and thus not trustworthy. + +
+
Exploit cryptographic hash collisions + +*Threat:* Exploit a cryptographic hash collision weakness to bypass one of the +other controls. + +*Mitigation:* Require cryptographically secure hash functions for commit +checksums and provenance subjects, such as SHA-256. + +*Examples:* Construct a benign file and a malicious file with the same SHA-1 +hash. Get the benign file reviewed and then submit the malicious file. +Alternatively, get the benign file reviewed and submitted and then build from +the malicious file. Solution: Only accept cryptographic hashes with strong +collision resistance. + +
+ +
+ + + +[authentic]: requirements.md#provenance-authentic +[exists]: requirements.md#provenance-exists +[isolated]: requirements.md#isolated +[unforgeable]: requirements.md#provenance-unforgeable +[supply chain threats]: threats-overview diff --git a/docs/spec/v1.1/use-cases.md b/docs/spec/v1.1/use-cases.md new file mode 100644 index 000000000..af55cfc1e --- /dev/null +++ b/docs/spec/v1.1/use-cases.md @@ -0,0 +1,129 @@ +--- +title: Use cases +description: SLSA protects against tampering during the software supply chain, but how? The answer depends on the use case in which SLSA is applied. Here are descriptions of the three main use cases for SLSA. +layout: standard +--- + +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 + +
+ +
+
+ +### First party + + + +
+
+ +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)](https://cloud.google.com/docs/security/binary-authorization-for-borg) + +
+
+ +
+
+ +### Open source + + + +
+
+ +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](https://documentation.suse.com/sbp/server-linux/html/SBP-SLSA4/index.html) + +
+
+ +
+
+ +### Vendors + + + +
+
+ +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. + +
+
+ +
+
+ +
+
+ +
+ +## Motivating example + +
+ +For a look at how SLSA might be applied to open source in the future, see the +[hypothetical curl example](../../example.md). + +
+
diff --git a/docs/spec/v1.1/verification_summary.md b/docs/spec/v1.1/verification_summary.md new file mode 100644 index 000000000..f09b7f85d --- /dev/null +++ b/docs/spec/v1.1/verification_summary.md @@ -0,0 +1,291 @@ +--- +title: SLSA Verification Summary Attestation (VSA) +description: SLSA v1.0 specification for a verification summary of artifacts by a trusted verifier entity. +layout: standard +--- + +Verification summary attestations communicate that an artifact has been verified +at a specific SLSA level and details about that verification. + +This document defines the following predicate type within the [in-toto +attestation] framework: + +```json +"predicateType": "https://slsa.dev/verification_summary/v1" +``` + +> Important: Always use the above string for `predicateType` rather than what is +> in the URL bar. The `predicateType` URI will always resolve to the latest +> minor version of this specification. See [parsing rules](#parsing-rules) for +> more information. + +## Purpose + +Describe what SLSA level an artifact or set of artifacts was verified at +and other details about the verification process including what SLSA level +the dependencies were verified at. + +This allows software consumers to make a decision about the validity of an +artifact without needing to have access to all of the attestations about the +artifact or all of its transitive dependencies. They can use it to delegate +complex policy decisions to some trusted party and then simply trust that +party's decision regarding the artifact. + +It also allows software producers to keep the details of their build pipeline +confidential while still communicating that some verification has taken place. +This might be necessary for legal reasons (keeping a software supplier +confidential) or for security reasons (not revealing that an embargoed patch has +been included). + +## Model + +A Verification Summary Attestation (VSA) is an attestation that some entity +(`verifier`) verified one or more software artifacts (the `subject` of an +in-toto attestation [Statement]) by evaluating the artifact and a `bundle` +of attestations against some `policy`. Users who trust the `verifier` may +assume that the artifacts met the indicated SLSA level without themselves +needing to evaluate the artifact or to have access to the attestations the +`verifier` used to make its determination. + +The VSA also allows consumers to determine the verified levels of +all of an artifact’s _transitive_ dependencies. The verifier does this by +either a) verifying the provenance of each non-source dependency listed in +the [resolvedDependencies](/provenance/v1#resolvedDependencies) of the artifact +being verified (recursively) or b) matching the non-source dependency +listed in `resolvedDependencies` (`subject.digest` == +`resolvedDependencies.digest` and, ideally, `vsa.resourceUri` == +`resolvedDependencies.uri`) to a VSA _for that dependency_ and using +`vsa.verifiedLevels` and `vsa.dependencyLevels`. Policy verifiers wishing +to establish minimum requirements on dependencies SLSA levels may use +`vsa.dependencyLevels` to do so. + +## Schema + +```jsonc +// Standard attestation fields: +"_type": "https://in-toto.io/Statement/v1", +"subject": [{ + "name": , + "digest": { } +}], + +// Predicate +"predicateType": "https://slsa.dev/verification_summary/v1", +"predicate": { + // Required + "verifier": { + "id": "" + }, + "timeVerified": , + "resourceUri": , + "policy": { + "uri": "", + "digest": { /* DigestSet */ } + } + "inputAttestations": [ + { + "uri": "", + "digest": { } + }, + ... + ], + "verificationResult": "", + "verifiedLevels": [""], + "dependencyLevels": { + "": , + "": , + ... + }, + "slsaVersion": ".", +} +``` + +### Parsing rules + +This predicate follows the in-toto attestation [parsing rules]. Summary: + +- Consumers MUST ignore unrecognized fields. +- The `predicateType` URI includes the major version number and will always + change whenever there is a backwards incompatible change. +- Minor version changes are always backwards compatible and "monotonic." Such + changes do not update the `predicateType`. +- Producers MAY add extension fields using field names that are URIs. + +### Fields + +_NOTE: This section describes the fields within `predicate`. For a description +of the other top-level fields, such as `subject`, see [Statement]._ + + +`verifier` _object, required_ + +> Identifies the entity that performed the verification. +> +> The identity MUST reflect the trust base that consumers care about. How +> detailed to be is a judgment call. +> +> Consumers MUST accept only specific (signer, verifier) pairs. For example, +> "GitHub" can sign provenance for the "GitHub Actions" verifier, and "Google" +> can sign provenance for the "Google Cloud Deploy" verifier, but "GitHub" cannot +> sign for the "Google Cloud Deploy" verifier. +> +> The field is required, even if it is implicit from the signer, to aid readability and +> debugging. It is an object to allow additional fields in the future, in case one +> URI is not sufficient. + + +`verifier.id` _string ([TypeURI]), required_ + +> URI indicating the verifier’s identity. + + +`timeVerified` _string ([Timestamp]), required_ + +> Timestamp indicating what time the verification occurred. + + +`resourceUri` _string ([ResourceURI]), required_ + +> URI that identifies the resource associated with the artifact being verified. + + +`policy` _object ([ResourceDescriptor]), required_ + +> Describes the policy that the `subject` was verified against. +> +> The entry MUST contain a `uri`. + + +`inputAttestations` _array ([ResourceDescriptor]), optional_ + +> The collection of attestations that were used to perform verification. +> Conceptually similar to the `resolvedDependencies` field in [SLSA Provenance]. +> +> This field MAY be absent if the verifier does not support this feature. +> If non-empty, this field MUST contain information on _all_ the attestations +> used to perform verification. +> +> Each entry MUST contain a `digest` of the attestation and SHOULD contains a +> `uri` that can be used to fetch the attestation. + + +`verificationResult` _string, required_ + +> Either “PASSED” or “FAILED” to indicate if the artifact passed or failed the policy verification. + + +`verifiedLevels` _array ([SlsaResult]), required_ + +> Indicates the highest level of each track verified for the artifact (and not +> its dependencies), or "FAILED" if policy verification failed. +> +> Users MUST NOT include more than one level per SLSA track. Note that each SLSA +> level implies all levels below it (e.g. SLSA_BUILD_LEVEL_3 implies +> SLSA_BUILD_LEVEL_2 and SLSA_BUILD_LEVEL_1), so there is no need to +> include more than one level per track. + + +`dependencyLevels` _object, optional_ + +> A count of the dependencies at each SLSA level. +> +> Map from [SlsaResult] to the number of the artifact's _transitive_ dependencies +> that were verified at the indicated level. Absence of a given level of +> [SlsaResult] MUST be interpreted as reporting _0_ dependencies at that level. +> +> Users MUST count each dependency only once per SLSA track, at the highest +> level verified. For example, if a dependency meets SLSA_BUILD_LEVEL_2, +> you include it with the count for SLSA_BUILD_LEVEL_2 but not the count for +>SLSA_BUILD_LEVEL_1. + + +`slsaVersion` _string, optional_ + +> Indicates the version of the SLSA specification that the verifier used, in the +> form `.`. Example: `1.0`. If unset, the default is an +> unspecified minor version of `1.x`. + +## Example + +WARNING: This is just for demonstration purposes. + +```jsonc +"_type": "https://in-toto.io/Statement/v1", +"subject": [{ + "name": "out/example-1.2.3.tar.gz", + "digest": {"sha256": "5678..."} +}], + +// Predicate +"predicateType": "https://slsa.dev/verification_summary/v1", +"predicate": { + "verifier": { + "id": "https://example.com/publication_verifier" + }, + "timeVerified": "1985-04-12T23:20:50.52Z", + "resourceUri": "https://example.com/example-1.2.3.tar.gz", + "policy": { + "uri": "https://example.com/example_tarball.policy", + "digest": {"sha256": "1234..."} + }, + "inputAttestations": [ + { + "uri": "https://example.com/provenances/example-1.2.3.tar.gz.intoto.jsonl", + "digest": {"sha256": "abcd..."} + } + ], + "verificationResult": "PASSED", + "verifiedLevels": ["SLSA_LEVEL_3"], + "dependencyLevels": { + "SLSA_BUILD_LEVEL_3": 5, + "SLSA_BUILD_LEVEL_2": 7, + "SLSA_BUILD_LEVEL_1": 1, + }, + "slsaVersion": "1.0" +} +``` + +
+ +## _SlsaResult (String)_ + +
+ +The result of evaluating an artifact (or set of artifacts) against SLSA. +SHOULD be one of these values: + +- SLSA_BUILD_LEVEL_0 +- SLSA_BUILD_LEVEL_1 +- SLSA_BUILD_LEVEL_2 +- SLSA_BUILD_LEVEL_3 +- FAILED (Indicates policy evaluation failed) + +Note that each SLSA level implies the levels below it. For example, +SLSA_BUILD_LEVEL_3 means (SLSA_BUILD_LEVEL_1 + SLSA_BUILD_LEVEL_2 + +SLSA_BUILD_LEVEL_3). + +Users MAY use custom values here but MUST NOT use custom values starting with +`SLSA_`. + +## Change history + +- 1: + - Replaced `materials` with `resolvedDependencies`. + - Relaxed `SlsaResult` to allow other values. + - Converted to lowerCamelCase for consistency with [SLSA Provenance]. + - Added `slsaVersion` field. +- 0.2: + - Added `resource_uri` field. + - Added optional `input_attestations` field. +- 0.1: Initial version. + +[SLSA Provenance]: /provenance +[SlsaResult]: #slsaresult +[DigestSet]: https://github.com/in-toto/attestation/blob/main/spec/v1/digest_set.md +[ResourceURI]: https://github.com/in-toto/attestation/blob/main/spec/v1/field_types.md#ResourceURI +[ResourceDescriptor]: https://github.com/in-toto/attestation/blob/main/spec/v1/resource_descriptor.md +[Statement]: https://github.com/in-toto/attestation/blob/main/spec/v1/statement.md +[Timestamp]: https://github.com/in-toto/attestation/blob/main/spec/v1/field_types.md#Timestamp +[TypeURI]: https://github.com/in-toto/attestation/blob/main/spec/v1/field_types.md#TypeURI +[in-toto attestation]: https://github.com/in-toto/attestation +[parsing rules]: https://github.com/in-toto/attestation/blob/main/spec/v1/README.md#parsing-rules diff --git a/docs/spec/v1.1/verifying-artifacts.md b/docs/spec/v1.1/verifying-artifacts.md new file mode 100644 index 000000000..ad9e17db6 --- /dev/null +++ b/docs/spec/v1.1/verifying-artifacts.md @@ -0,0 +1,301 @@ +--- +title: Verifying artifacts +description: SLSA uses provenance to indicate whether an artifact is authentic or not, but provenance doesn't do anything unless somebody inspects it. SLSA calls that inspection verification, and this page describes how to verify artifacts and their SLSA provenenance. The intended audience is platform implementers, security engineers, and software consumers. +--- + +SLSA uses provenance to indicate whether an artifact is authentic or not, but +provenance doesn't do anything unless somebody inspects it. SLSA calls that +inspection **verification**, and this page describes recommendations for how to +verify artifacts and their SLSA provenance. + +This page is divided into several sections. The first describes the process +for verifying an artifact and its provenance against a set of expectations. The +second describes how to form the expectations used to verify provenance. The +third discusses architecture choices for where provenance verification can +happen. + +## How to verify + +Verification SHOULD include the following steps: + +- Ensuring that the builder identity is one of those in the map of trusted + builder id's to SLSA level. +- Verifying the signature on the provenance envelope. +- Ensuring that the values for `buildType` and `externalParameters` in the + provenance match the expected values. The package ecosystem MAY allow + an approved list of `externalParameters` to be ignored during verification. + Any unrecognized `externalParameters` SHOULD cause verification to fail. + +![Threats covered by each step](images/supply-chain-threats-build-verification.svg) + +See [Terminology](terminology.md) for an explanation of supply chain model and +[Threats & mitigations](threats.md) for a detailed explanation of each threat. + +**Note:** This section assumes that the provenance is in the recommended +[provenance format](/provenance/v1). If it is not, then the verifier SHOULD +perform equivalent checks on provenance fields that correspond to the ones +referenced here. + +### Step 1: Check SLSA Build level + +[Step 1]: #step-1-check-slsa-build-level + +First, check the SLSA Build level by comparing the artifact to its provenance +and the provenance to a preconfigured root of trust. The goal is to ensure that +the provenance actually applies to the artifact in question and to assess the +trustworthiness of the provenance. This mitigates some or all of [threats] "E", +"F", "G", and "H", depending on SLSA Build level and where verification happens. + +Once, when bootstrapping the verifier: + +- Configure the verifier's roots of trust, meaning the recognized builder + identities and the maximum SLSA Build level each builder is trusted up to. + Different verifiers might use different roots of trust, but usually a + verifier uses the same roots of trust for all packages. This configuration + is likely in the form of a map from (builder public key identity, + `builder.id`) to (SLSA Build level) drawn from the SLSA Conformance + Program (coming soon). + +
+ Example root of trust configuration + + The following snippet shows conceptually how a verifier's roots of trust + might be configured using made-up syntax. + + ```jsonc + "slsaRootsOfTrust": [ + // A builder trusted at SLSA Build L3, using a fixed public key. + { + "publicKey": "HKJEwI...", + "builderId": "https://somebuilder.example.com/slsa/l3", + "slsaBuildLevel": 3 + }, + // A different builder that claims to be SLSA Build L3, + // but this verifier only trusts it to L2. + { + "publicKey": "tLykq9...", + "builderId": "https://differentbuilder.example.com/slsa/l3", + "slsaBuildLevel": 2 + }, + // A builder that uses Sigstore for authentication. + { + "sigstore": { + "root": "global", // identifies fulcio/rekor roots + "subjectAlternativeNamePattern": "https://github.com/slsa-framework/slsa-github-generator/.github/workflows/generator_generic_slsa3.yml@refs/tags/v*.*.*" + } + "builderId": "https://github.com/slsa-framework/slsa-github-generator/.github/workflows/generator_generic_slsa3.yml@refs/tags/v*.*.*", + "slsaBuildLevel": 3, + } + ... + ], + ``` + +
+ +Given an artifact and its provenance: + +1. [Verify][processing-model] the envelope's signature using the roots of + trust, resulting in a list of recognized public keys (or equivalent). +2. [Verify][processing-model] that statement's `subject` matches the digest of + the artifact in question. +3. Verify that the `predicateType` is `https://slsa.dev/provenance/v1`. +4. Look up the SLSA Build Level in the roots of trust, using the recognized + public keys and the `builder.id`, defaulting to SLSA Build L1. + +Resulting threat mitigation: + +- [Threat "E"]: SLSA Build L3 requires protection against compromise of the + build process and provenance generation by an external adversary, such as + persistence between builds or theft of the provenance signing key. In other + words, SLSA Build L3 establishes that the provenance is accurate and + trustworthy, assuming you trust the build platform. + - IMPORTANT: SLSA Build L3 does **not** cover compromise of the build + platform itself, such as by a malicious insider. Instead, verifiers + SHOULD carefully consider which build platforms are added to the roots + of trust. For advice on establishing trust in build platforms, see + [Verifying build platforms](verifying-systems). +- [Threat "F"]: SLSA Build L2 covers tampering of the artifact or provenance + after the build. This is accomplished by verifying the `subject` and + signature in the steps above. +- [Threat "G"]: Verification by the consumer or otherwise outside of the + package registry covers compromise of the registry itself. (Verifying within + the registry at publication time is also valuable, but does not cover Threat + "G" or "H".) +- [Threat "H"]: Verification by the consumer covers compromise of the package + in transit. (Many ecosystems also address this threat using package + signatures or checksums.) + - NOTE: SLSA does not cover adversaries tricking a consumer to use an + unintended package, such as through typosquatting. + +[Threat "E"]: threats#e-compromise-build-process +[Threat "F"]: threats#f-upload-modified-package +[Threat "G"]: threats#g-compromise-package-repo +[Threat "H"]: threats#h-use-compromised-package + +[processing-model]: https://github.com/in-toto/attestation/tree/main/spec#processing-model + +### Step 2: Check expectations + +[verify-step-2]: #check-expectations + +Next, check that the package's provenance meets your expectations for that +package in order to mitigate [threat "C"]. + +In our threat model, the adversary has ability to invoke a build and to publish +to the registry. The adversary is not able to write to the source repository, nor do +they have insider access to any trusted systems. Your expectations SHOULD be +sufficient to detect or prevent this adversary from injecting unofficial +behavior into the package. + +You SHOULD compare the provenance against expected values for at least the +following fields: + +| What | Why | +| ---- | --- | +| Builder identity from [Step 1] | To prevent an adversary from building the correct code on an unintended platform | +| Canonical source repository | To prevent an adversary from building from an unofficial fork (or other disallowed source) | +| `buildType` | To ensure that `externalParameters` are interpreted as intended | +| `externalParameters` | To prevent an adversary from injecting unofficial behavior | + +Verification tools SHOULD reject unrecognized fields in `externalParameters` to +err on the side of caution. It is acceptable to allow a parameter to have a +range of values (possibly any value) if it is known that any value in the range +is safe. JSON comparison is sufficient for verifying parameters. + +TIP: Difficulty in forming meaningful expectations about `externalParameters` can +be a sign that the `buildType`'s level of abstraction is too low. For example, +`externalParameters` that record a list of commands to run is likely impractical +to verify because the commands change on every build. Instead, consider a +`buildType` that defines the list of commands in a configuration file in a +source repository, then put only the source repository in +`externalParameters`. Such a design is easier to verify because the source +repository is constant across builds. + +[Threat "C"]: threats#c-build-from-modified-source + +### Step 3: (Optional) Check dependencies recursively + +[verify-step-3]: #step-3-optional-check-dependencies-recursively + +Finally, recursively check the `resolvedDependencies` as available and to the +extent desired. Note that SLSA v1.0 does not have any requirements on the +completeness or verification of `resolvedDependencies`. However, one might wish +to verify dependencies in order to mitigate [threat "E"] and protect against +threats further up the supply chain. If `resolvedDependencies` is incomplete, +these checks can be done on a best-effort basis. + +A [Verification Summary Attestation (VSA)][VSA] can make dependency verification +more efficient by recording the result of prior verifications. A trimming +heuristic or exception mechanism is almost always necessary when verifying +dependencies because there will be transitive dependencies that are SLSA Build +L0. (For example, consider the compiler's compiler's compiler's ... compiler.) + +[Threat "E"]: threats#e-use-compromised-dependency +[VSA]: /verification_summary +[threats]: threats + +## Forming Expectations + +Expectations are known provenance values that indicate the +corresponding artifact is authentic. For example, a package ecosystem may +maintain a mapping between package names and their canonical source +repositories. That mapping constitutes a set of expectations. + +Possible models for forming expectations include: + +- **Trust on first use:** Accept the first version of the package as-is. On + each version update, compare the old provenance to the new provenance and + alert on any differences. This can be augmented by having rules about what + changes are benign, such as a parameter known to be safe or a heuristic + about safe git branches or tags. + +- **Defined by producer:** The package producer tells the verifier what their + expectations ought to be. In this model, the verifier SHOULD provide an + authenticated communication mechanism for the producer to set the package's + expectations, and there SHOULD be some protection against an adversary + unilaterally modifying them. For example, modifications might require + two-party control, or consumers might have to accept each policy change + (another form of trust on first use). + +- **Defined in source:** The source repository tells the verifier what their + expectations ought to be. In this model, the package name is immutably bound + to a source repository and all other external parameters are defined in the + source repository. This is how the Go ecosystem works, for example, since + the package name *is* the source repository location. + +It is important to note that expectations are tied to a *package name*, whereas +provenance is tied to an *artifact*. Different versions of the same package name +will likely have different artifacts and therefore different provenance. Similarly, an +artifact might have different names in different package ecosystems but use the same +provenance file. + +## Architecture options + +There are several options (non-mutually exclusive) for where provenance verification +can happen: the package ecosystem at upload time, the consumers at download time, or +via a continuous monitoring system. Each option comes with its own set of +considerations, but all are valid and at least one SHOULD be used. + +More than one component can verify provenance. For example, even if a package +ecosystem verifies provenance, consumers who get artifacts from that package +ecosystem might wish to verify provenance themselves for defense in depth. They +can do so using either client-side verification tooling or by polling a +monitor. + + + +### Package ecosystem + +[Package ecosystem]: #package-ecosystem + +A package ecosystem is a set of rules and conventions governing +how packages are distributed. Every package artifact has an ecosystem, whether it is +formal or ad-hoc. Some ecosystems are formal, such as language distribution +(e.g. [Python/PyPA](https://www.pypa.io)), operating system distribution (e.g. +[Debian/Apt](https://wiki.debian.org/DebianRepository/Format)), or artifact +distribution (e.g. [OCI](https://github.com/opencontainers/distribution-spec)). +Other ecosystems are informal, such as a convention used within a company. Even +ad-hoc distribution of software, such as through a link on a website, is +considered an "ecosystem". For more background, see +[Package Model](terminology.md#package-model). + +During package upload, a package ecosystem can ensure that the artifact's +provenance matches the expected values for that package name's provenance before +accepting it into the package registry. This option is RECOMMENDED whenever +possible because doing so benefits all of the package ecosystem's clients. + +The package ecosystem is responsible for making its expectations available to +consumers, reliably redistributing artifacts and provenance, and providing tools +to enable safe artifact consumption (e.g. whether an artifact meets +expectations). + +### Consumer + +[Consumer]: #consumer + +A package artifact's consumer is the organization or individual that uses the +package artifact. + +Consumers can form their own expectations for artifacts or use the default +expectations provided by the package producer and/or package ecosystem. +When forming their own expectations, the consumer uses client-side verification tooling to ensure +that the artifact's provenance matches their expectations for that package +before use (e.g. during installation or deployment). Client-side verification +tooling can be either standalone, such as +[slsa-verifier](https://github.com/slsa-framework/slsa-verifier), or built into +the package ecosystem client. + +### Monitor + +[Monitor]: #monitor + +A monitor is a service that verifies provenance for a set +of packages and publishes the result of that verification. The set of +packages verified by a monitor is arbitrary, though it MAY mimic the set +of packages published through one or more package ecosystems. The monitor +SHOULD publish its expectations for all the packages it verifies. + +Consumers can continuously poll a monitor to detect artifacts that +do not meet the monitor's expectations. Detecting artifacts that fail +verification is of limited benefit unless a human or automated system takes +action in response to the failed verification. diff --git a/docs/spec/v1.1/verifying-systems.md b/docs/spec/v1.1/verifying-systems.md new file mode 100644 index 000000000..6e9d9c07b --- /dev/null +++ b/docs/spec/v1.1/verifying-systems.md @@ -0,0 +1,238 @@ +--- +title: Verifying build platforms +description: Guidelines for assessing build platform security. +--- + +One of SLSA's guiding [principles](principles.md) is to "trust platforms, verify +artifacts". However, consumers cannot trust platforms to produce Build L3 +artifacts and provenance unless they have some proof that the provenance is +[unforgeable](requirements.md#provenance-unforgeable) and the builds are +[isolated](requirements.md#isolated). + +This page describes the parts of a build platform that consumers SHOULD assess +and provides sample questions consumers can ask when assessing a build platform. +See also [Threats & mitigations](threats.md) and the +[build model](terminology.md#build-model). + +## Threats + +### Adversary goal + +The SLSA Build track defends against an adversary whose primary goal is to +inject unofficial behavior into a package artifact while avoiding detection. +Remember that [verifiers](verifying-artifacts.md) only accept artifacts whose +provenance matches expectations. To bypass this, the adversary tries to either +(a) tamper with a legitimate build whose provenance already matches +expectations, or (b) tamper with an illegitimate build's provenance to make it +match expectations. + +More formally, if a build with external parameters P would produce an artifact +with binary hash X and a build with external parameters P' would produce an +artifact with binary hash Y, they wish to produce provenance indicating a build +with external parameters P produced an artifact with binary hash Y. + +See threats [C], [D], [E], and [F] for examples of specific threats. + +Note: Platform abuse (e.g. running non-build workloads) and attacks against +builder availability are out of scope of this document. + +### Adversary profiles + +Consumers SHOULD also evaluate the build platform's ability to defend against the +following types of adversaries. + +1. Project contributors, who can: + - Create builds on the build platform. These are the adversary's controlled + builds. + - Modify one or more controlled builds' external parameters. + - Modify one or more controlled builds' environments and run arbitrary + code inside those environments. + - Read the target build's source repo. + - Fork the target build's source repo. + - Modify a fork of the target build's source repo and build from it. +2. Project maintainer, who can: + - Do everything listed under "project contributors". + - Create new builds under the target build's project or identity. + - Modify the target build's source repo and build from it. + - Modify the target build's configuration. +3. Build platform administrators, who can: + - Do everything listed under "project contributors" and "project + maintainers". + - Run arbitrary code on the build platform. + - Read and modify network traffic. + - Access the control plane's cryptographic secrets. + - Remotely access build environments (e.g. via SSH). + +[C]: threats.md#c-build-from-modified-source +[D]: threats.md#d-use-compromised-dependency +[E]: threats.md#e-compromise-build-process +[F]: threats.md#f-upload-modified-package + +## Build platform components + +Consumers SHOULD consider at least these five elements of the +[build model](terminology.md#build-model) when assessing build platforms for SLSA +conformance: external parameters, control plane, build environments, caches, +and outputs. + +![image](images/build-model.svg) + +The following sections detail these elements of the build model and give prompts +for assessing a build platform's ability to produce SLSA Build L3 provenance. The +assessment SHOULD take into account the security model used to identify the +transitive closure of the `builder.id` for the [provenance model], specifically +around the platform's boundaries, actors, and interfaces. + +### External parameters + +External parameters are the external interface to the builder and include all +inputs to the build process. Examples include the source to be built, the build +definition/script to be executed, user-provided instructions to the +control plane for how to create the build environment (e.g. which operating +system to use), and any additional user-provided strings. + +#### Prompts for assessing external parameters + +- How does the control plane process user-provided external parameters? + Examples: sanitizing, parsing, not at all +- Which external parameters are processed by the control plane and which are + processed by the build environment? +- What sort of external parameters does the control plane accept for + build environment configuration? +- How do you ensure that all external parameters are represented in the + provenance? +- How will you ensure that future design changes will not add additional + external parameters without representing them in the provenance? + +### Control plane + +The control plane is the build platform component that orchestrates each +independent build execution. It is responsible for setting up each build and +cleaning up afterwards. At SLSA Build L2+ the control plane generates and signs +provenance for each build performed on the build platform. The control plane is +operated by one or more administrators, who have privileges to modify the +control plane. + +#### Prompts for assessing the control plane + +- Administration + - What are the ways an employee can use privileged access to influence a + build or provenance generation? Examples: physical access, terminal + access, access to cryptographic secrets + - What controls are in place to detect or prevent the employee from + abusing such access? Examples: two-person approvals, audit logging, + workload identities + - Roughly how many employees have such access? + - How are privileged accounts protected? Examples: two-factor + authentication, client device security policies + - What plans do you have for recovering from security incidents and platform + outages? Are they tested? How frequently? + +- Provenance generation + - How does the control plane observe the build to ensure the provenance's + accuracy? + - Are there situations in which the control plane will not generate + provenance for a completed build? What are they? + +- Development practices + - How do you track the control plane's software and configuration? + Example: version control + - How do you build confidence in the control plane's software supply + chain? Example: SLSA L3+ provenance, build from source + - How do you secure communications between builder components? Example: + TLS with certificate transparency. + - Are you able to perform forensic analysis on compromised build + environments? How? Example: retain base images indefinitely + +- Creating build environments + - How does the control plane share data with build environments? Example: + mounting a shared file system partition + - How does the control plane protect its integrity from build + environments? Example: not mount its own file system partitions on + build environments + - How does the control plane prevent build environments from accessing its + cryptographic secrets? Examples: dedicated secret storage, not mounting + its own file system partitions to build environments, hardware security + modules + +- Managing cryptographic secrets + - How do you store the control plane's cryptographic secrets? + - Which parts of the organization have access to the control plane's + cryptographic secrets? + - What controls are in place to detect or prevent employees abusing such + access? Examples: two-person approvals, audit logging + - How are secrets protected in memory? Examples: secrets are stored in + hardware security modules and backed up in secure cold storage + - How frequently are cryptographic secrets rotated? Describe the rotation + process. + - What is your plan for remediating cryptographic secret compromise? How + frequently is this plan tested? + +### Build environment + +The build environment is the independent execution context where the build +takes place. In the case of a distributed build, the build environment is the +collection of all execution contexts that run build steps. Each build +environment must be isolated from the control plane and from all other build +environments, including those running builds from the same tenant or project. +Tenants are free to modify the build environment arbitrarily. Build +environments must have a means to fetch input artifacts (source, dependencies, +etc). + +#### Prompts for assessing build environments + +- Isolation technologies + - How are build environments isolated from the control plane and each + other? Examples: VMs, containers, sandboxed processes + - How is separation achieved between trusted and untrusted processes? + - How have you hardened your build environments against malicious tenants? + Examples: configuration hardening, limiting attack surface + - How frequently do you update your isolation software? + - What is your process for responding to vulnerability disclosures? What + about vulnerabilities in your dependencies? + - What prevents a malicious build from gaining persistence and influencing + subsequent builds? + +- Creation and destruction + - What operating system and utilities are available in build environments + on creation? How were these elements chosen? Examples: A minimal Linux + distribution with its package manager, OSX with HomeBrew + - How long could a compromised build environment remain active in the + build platform? + +- Network access + - Are build environments able to call out to remote execution? If so, how + do you prevent them from tampering with the control plane or other build + environments over the network? + - Are build environments able to open services on the network? If so, how + do you prevent remote interference through these services? + +### Cache + +Builders may have zero or more caches to store frequently used dependencies. +Build environments may have either read-only or read-write access to caches. + +#### Prompts for assessing caches + +- What sorts of caches are available to build environments? +- How are those caches populated? +- How are cache contents validated before use? + +### Output storage + +Output Storage holds built artifacts and their provenance. Storage may either be +shared between build projects or allocated separately per-project. + +#### Prompts for assessing output storage + +- How do you prevent builds from reading or overwriting files that belong to + another build? Example: authorization on storage +- What processing, if any, does the control plane do on output artifacts? + +## Builder evaluation + +Organizations can either self-attest to their answers or seek certification from +a third-party auditor. Evidence for self-attestation should be published on +the internet and can include information such as the security model defined as +part of the provenance. Evidence submitted for third-party certification need not +be published. diff --git a/docs/spec/v1.1/whats-new.md b/docs/spec/v1.1/whats-new.md new file mode 100644 index 000000000..7ef772722 --- /dev/null +++ b/docs/spec/v1.1/whats-new.md @@ -0,0 +1,202 @@ +--- +title: What's new in SLSA v1.0 +description: SLSA v1.0 is the first stable release of SLSA. This document describes what has changed since v0.1. +--- + +SLSA v1.0 is the first stable release of SLSA, creating a solid foundation on +which future versions can expand. This document describes the major changes in +v1.0 relative to the prior release, [v0.1]. + +## Summary of changes + +SLSA v1.0 is a significant rework of the specification in response to ongoing +feedback, filed issues, suggestions for course corrections, and other input from +the SLSA community and early adopters. Overall, the changes prioritize +simplicity, practicality, and stability. + +Overall, SLSA v1.0 is more stable and better defined than v0.1, but less +ambitious. It corresponds roughly to the build and provenance requirements of +the prior version's SLSA Levels 1 through 3, deferring SLSA Level 4 and the +source and common requirements to a future version. The rationale is explained +[below][stability]. + +Other significant changes: + +- [Division of the levels into multiple tracks][tracks], which are separate + sets of levels that measure different aspects of software supply chain + security +- [Reorganization and simplification of the core specification][core-spec] to + make it easier to understand and to provide better guidance +- [New guidance on verification][verification] of artifacts and build systems +- [Updated provenance and VSA schemas][provenance-spec], with a clearer build + model + +## Stability and scope + +[stability]: #stability-and-scope + +The v1.0 release marks the first stable version of SLSA. We are confident that +the specification represents broad consensus and will not change significantly +in the future. Having a stable foundation enables organizations and ecosystems +to begin implementing and adopting SLSA with minimal risk of future breaking +changes. + +That said, some concepts from v0.1 had to be deferred to a [future +version][future] in order to allow us to release v1.0 in a reasonable time +frame. The deferred concepts---source requirements, hermetic builds (SLSA L4), +and common requirements---were at significant risk of breaking changes in the +future to address concerns from v0.1. We believed it was more valuable to +release a small but stable base now while we work towards solidifying those +concepts in a future version. + +Going forward, we commit to a consistent [versioning](/spec-stages#versioning) +scheme based on semantic versioning. Backwards-incompatible changes will result +in a major version increase (v2.0, v3.0, etc.); significant backwards-compatible +changes will result in a minor version increase (v1.1, v1.2, etc.), while +editorial changes may be made without a version increase. + +For further explanation of the decisions behind v1.0, see the [SLSA v1.0 +Proposal][proposal]. + +## Tracks + +[Tracks]: #tracks + +A significant conceptual change from v0.1 is the division of SLSA's level +requirements into multiple tracks. Previously, each SLSA level encompassed +requirements across multiple software supply chain aspects: there were source, +build, provenance, and common requirements. To reach a particular level, +adopters needed to meet [all requirements in each of the four areas][v0.1-reqs]. +Organizing the specification in that way made adoption cumbersome, since +requirements were split across unrelated domains—improvements in one area were +not recognized until improvements were made in all areas. + +Now, the requirements are divided into SLSA tracks that each focus on one area +of the software supply chain. We anticipate this division will make SLSA +adoption easier for users. Division into tracks also benefits the SLSA +community: developers contributing to SLSA can parallelize work on multiple +tracks without blocking each other, and members of the community can contribute +specifically to their areas of expertise. + +SLSA v1.0 defines the SLSA Build track to begin this separation of +requirements, with other tracks to come in future versions. The new +[SLSA Build track Levels 1-3](levels#build-track) roughly +correspond to [Levels 1-3 of v0.1](requirements#build-requirements), +minus the source requirements. We anticipate future versions of the +specification to continue building on requirements without changing the existing +requirements defined in v1.0. The specification will likely expand to +incorporate both new tracks and additional levels for existing tracks. We +currently have [plans][future] for Build Level 4 and a Source track. + +The v1.0 also defines the [principles](principles) behind SLSA track +requirements, which will guide future track additions. For more information +about the rationale for tracks, see the [proposal]. + +## Improvements to core specification + +[core-spec]: #improvements-to-core-specification + +We've simplified and reorganized the specification to make it easier to +understand and apply. We've also split the requirements into multiple pages to +better reflect the division of labor across the software supply chain: producing +artifacts, distributing provenance, verifying artifacts, and verifying build +platforms. + +[Terminology](terminology) has been expanded to fully define all necessary +concepts and to be consistent across the specification. + +[Security levels](levels) has been completely rewritten to provide a high +level overview of the SLSA [tracks] and levels. Importantly, it explains the +benefits provided by each level. + +[Producing artifacts](requirements) explains requirements for the software +producer and the build platform. While the requirements are largely the same as +before---aside from those [deferred][stability] to a future version---there are +some minor changes to make SLSA easier to adopt. These changes include: +renaming, simplifying, and merging some requirements; removing the redundant +"scripted build" and "config as code" requirements; merging of the provenance +requirements into the recommended [provenance format][provenance-spec]; and +splitting the requirements between those for the Producer and the Build +platform. + +[Distributing provenance](distributing-provenance) *(new for v1.0)* provides +guidance to software producers and package ecosystems on how to distribute +provenance alongside artifacts. We hope this brings consistency across open +source package ecosystems as they adopt SLSA. + +[Verifying artifacts](verifying-artifacts) *(new for v1.0)* provides guidance to +package ecosystems and consumers for how to verify provenance and compare it to +expectations. It is discussed more in the following section. + +[Verifying build platforms](verifying-systems) *(new for v1.0)* provides a list +of prompts for evaluating a build platform's SLSA conformance. It covers similar +ground as v0.1's common requirements, but in a different form. It is also +discussed in the following section. + +[Threats & mitigations](threats) has been updated for v1.0, filling out parts +that were missing in v0.1. Note that labels D and E have swapped positions from +v0.1 to align with the grouping of Source (A-C), Dependency (D), and Build (E-H) +threats. + +## Verification + +[verification]: #verification + +Another significant change in the v1.0 is documenting the need for provenance +verification. + +SLSA v0.1 specified guidance for how to produce provenance but not how to verify +it. This left a large gap as most threats targeted by SLSA are only mitigated by +verifying provenance and comparing it to expectations. + +SLSA v1.0 addresses this gap by providing more explicit guidance on how to +verify provenance. This is split between establishing +[trust in build platforms](verifying-systems) themselves versus establishing +[trust in artifacts](verifying-artifacts) produced by those build platforms. +Build platforms implement the requirements around isolation and provenance +generation, and consumers choose whether to trust those build platforms. Once +that trust is established, consumers or package managers can verify artifacts by +comparing the provenance to expectations for the package in question. + +Ecosystems are already creating verification tooling, such as [npm's forthcoming +SLSA support](https://github.com/github/roadmap/issues/612). Tooling for +organizations that need to protect first-party software is also available, such +as [slsa-verifier](https://github.com/slsa-framework/slsa-verifier). + +## Provenance and VSA formats + +[provenance-spec]: #provenance-and-vsa-formats + +SLSA v1.0 simplifies SLSA's build model and recommended provenance format to +make it easier to understand and apply to arbitrary build platforms. + +A major source of confusion for SLSA v0.1 was how to model a build and represent +it in provenance. The v0.1 spec and v0.x provenance formats were overly rigid +about a build's inputs, differentiating between "source", "build config", "entry +point", and so on. Many implementers found that their build platforms did not +clearly fit into this model, and the intent of each field was not clear. +Furthermore, provenance requirements were described both abstractly in the SLSA +specification and concretely in the provenance format, using different language. +Implementers needed to jump back and forth and mentally map one concept to +another. + +SLSA v1.0 and the recommended [provenance v1 format](/provenance/v1) attempt to +address this confusion by simplifying the model and aligning terminology between +the two. The main change is to represent all "external parameters" that are +exposed to the build platform's users, instead of differentiating between +various inputs. Now, you can represent arbitrary parameters, as long as it is +possible to compare these parameters to expectations. Other parts of the +provenance format were renamed, though most concepts translate from the old +format to the new format. For a detailed list of changes, see +[provenance change history](/provenance/v1#change-history). + +In addition, the recommended +[verification summary attestation (VSA)](/verification_summary/v1) has been +updated to v1.0. + + + +[future]: future-directions +[proposal]: https://github.com/slsa-framework/slsa-proposals/blob/main/0003/README.md +[v0.1-reqs]: /spec/v0.1/requirements +[v0.1]: /spec/v0.1/