Add release artifact signing KEP

Signed-off-by: Sascha Grunert <[email protected]>

keps/sig-release/3031-signing-release-artifacts/README.md

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+# KEP-3031: Signing release artifacts
+
+<!-- toc -->
+
+- [Release Signoff Checklist](#release-signoff-checklist)
+- [Summary](#summary)
+- [Motivation](#motivation)
+  - [Goals](#goals)
+  - [Non-Goals](#non-goals)
+- [Proposal](#proposal)
+  - [User Stories (Optional)](#user-stories-optional)
+  - [Risks and Mitigations](#risks-and-mitigations)
+  - [Graduation Criteria](#graduation-criteria)
+    - [Alpha](#alpha)
+    - [Beta](#beta)
+    - [GA](#ga)
+- [Drawbacks](#drawbacks)
+- [Alternatives](#alternatives)
+- [Implementation History](#implementation-history)
+<!-- /toc -->
+
+## Release Signoff Checklist
+
+<!--
+**ACTION REQUIRED:** In order to merge code into a release, there must be an
+issue in [kubernetes/enhancements] referencing this KEP and targeting a release
+milestone **before the [Enhancement Freeze](https://git.k8s.io/sig-release/releases)
+of the targeted release**.
+
+For enhancements that make changes to code or processes/procedures in core
+Kubernetes—i.e., [kubernetes/kubernetes], we require the following Release
+Signoff checklist to be completed.
+
+Check these off as they are completed for the Release Team to track. These
+checklist items _must_ be updated for the enhancement to be released.
+-->
+
+Items marked with (R) are required _prior to targeting to a milestone / release_.
+
+- [ ] (R) Enhancement issue in release milestone, which links to KEP dir in [kubernetes/enhancements] (not the initial KEP PR)
+- [ ] (R) KEP approvers have approved the KEP status as `implementable`
+- [ ] (R) Design details are appropriately documented
+- [ ] (R) Test plan is in place, giving consideration to SIG Architecture and SIG Testing input (including test refactors)
+  - [ ] e2e Tests for all Beta API Operations (endpoints)
+  - [ ] (R) Ensure GA e2e tests for meet requirements for [Conformance Tests](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/conformance-tests.md)
+  - [ ] (R) Minimum Two Week Window for GA e2e tests to prove flake free
+- [ ] (R) Graduation criteria is in place
+  - [ ] (R) [all GA Endpoints](https://github.com/kubernetes/community/pull/1806) must be hit by [Conformance Tests](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/conformance-tests.md)
+- [ ] (R) Production readiness review completed
+- [ ] (R) Production readiness review approved
+- [ ] "Implementation History" section is up-to-date for milestone
+- [ ] User-facing documentation has been created in [kubernetes/website], for publication to [kubernetes.io]
+- [ ] Supporting documentation—e.g., additional design documents, links to mailing list discussions/SIG meetings, relevant PRs/issues, release notes
+
+<!--
+**Note:** This checklist is iterative and should be reviewed and updated every time this enhancement is being considered for a milestone.
+-->
+
+[kubernetes.io]: https://kubernetes.io/
+[kubernetes/enhancements]: https://git.k8s.io/enhancements
+[kubernetes/kubernetes]: https://git.k8s.io/kubernetes
+[kubernetes/website]: https://git.k8s.io/website
+
+## Summary
+
+Target of this enhancement is to define which technology the Kubernetes
+community is using to signs release artifacts.
+
+## Motivation
+
+Signing artifacts provides end users a chance to verify the integrity of the
+downloaded resource. It allows to mitigate man-in-the-middle attacks directly on
+the client side and therefore ensures the trustfulness of the remote serving the
+artifacts.
+
+### Goals
+
+- Defining the used tooling for signing all Kubernetes related artifacts
+- Providing a standard signing process for related projects (like k/release)
+
+### Non-Goals
+
+- Discussing not user-facing internal technical implementation details
+
+## Proposal
+
+Every Kubernetes release produces a set of artifacts. We define artifacts as
+something consumable by end users. Artifacts can be binaries, container images,
+checksum files, documentation, provenance metadata, or the software bill of
+materials. None of those end-user resources are signed right now.
+
+The overall goal of SIG Release is to unify the way how to sign artifacts. This
+will be done by relying on the tools of the Linux Foundations digital signing
+project [sigstore](https://www.sigstore.dev). This goal aligns with the
+[Roadmap and Vision](https://github.com/kubernetes/sig-release/blob/f62149/roadmap.md)
+of SIG Release to provide a secure software supply chain for Kubernetes. It also
+joins the effort of gaining full SLSA Compliance in the Kubernetes Release
+Process ([KEP-3027](https://github.com/kubernetes/enhancements/issues/3027)).
+Because of that, the future [SLSA](https://slsa.dev) compliance of artifacts
+produced by SIG release will require signing artifacts starting from level 2.
+
+[cosign](https://github.com/sigstore/cosign) will be the tool of our choice when
+speaking about the technical aspects of the solution. How we integrate the
+projects into our build process in k/release is out of scope of this KEP and
+will be discussed in the Release Engineering subproject of SIG Release. A
+pre-evaluation of the tool has been done already to ensure that it meets the
+requirements.
+
+An [ongoing discussion](https://github.com/kubernetes/release/issues/2227) about
+using cosign already exists in k/release. This issue contains technical
+discussions about how to utilize the existing Google infrastructure as well as
+consider utilizing keyless signing via workload identities. Nevertheless, this
+KEP focuses more on the "What" aspects rather than the "How".
+
+### User Stories (Optional)
+
+- As an end user, I would like to be able to verify the Kubernetes release
+  artifacts, so that I can mitigate possible resource modifications by the
+  network.
+
+### Risks and Mitigations
+
+- **Risk:** Unauthorized access to the signing key or its infrastructure
+
+  **Mitigation:** Storing the credentials in a secure Google Cloud Project with
+  limited access for SIG Release. Enabling the cosign [transparency log
+  (Rekor)](https://github.com/sigstore/cosign#rekor-support) to make the key
+  usage publicly auditable.
+
+### Graduation Criteria
+
+#### Alpha
+
+- Outline and integrate an example process for signing Kubernetes release
+  artifacts.
+
+#### Beta
+
+- Standard Kubernetes release artifacts (binaries and container images) are
+  signed.
+
+#### GA
+
+- All Kubernetes artifacts are signed. This does exclude everything which gets
+  build outside of the main Kubernetes repository.
+
+## Drawbacks
+
+- The initial implementation effort from the release engineering perspective
+  requires adding an additional layer of complexity to the Kubernetes build
+  pipeline.
+
+## Alternatives
+
+- Using the [OCI Registry As Storage (ORAS) project](https://github.com/oras-project/oras)
+
+## Implementation History
+
+- 2021-11-29 Initial Draft

keps/sig-release/3031-signing-release-artifacts/kep.yaml

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+title: Signing release artifacts
+kep-number: 3031
+authors:
+  - "@saschagrunert"
+owning-sig: sig-release
+participating-sigs:
+  - sig-security
+status: provisional
+creation-date: 2021-11-02
+reviewers:
+  - TBD
+approvers:
+  - TBD
+
+##### WARNING !!! ######
+# prr-approvers has been moved to its own location
+# You should create your own in keps/prod-readiness
+# Please make a copy of keps/prod-readiness/template/nnnn.yaml
+# to keps/prod-readiness/sig-xxxxx/00000.yaml (replace with kep number)
+#prr-approvers:
+
+# see-also:
+#   - "/keps/sig-aaa/1234-we-heard-you-like-keps"
+#   - "/keps/sig-bbb/2345-everyone-gets-a-kep"
+# replaces:
+#   - "/keps/sig-ccc/3456-replaced-kep"
+
+# The target maturity stage in the current dev cycle for this KEP.
+stage: alpha
+
+# The most recent milestone for which work toward delivery of this KEP has been
+# done. This can be the current (upcoming) milestone, if it is being actively
+# worked on.
+latest-milestone: "v1.23"
+
+# The milestone at which this feature was, or is targeted to be, at each stage.
+milestone:
+  alpha: "v1.23"
+  # beta: "v1.20"
+  # stable: "v1.22"
+
+# The following PRR answers are required at beta release
+# metrics:
+#   - my_feature_metric