Add support for SigningConfig for sign-blob/attest-blob, support Rekor v2 #4319
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Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
## main #4319 +/- ##
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Verified working against our staging Rekor v2 instance: And for attestations... |
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Proof it's using Rekor v2: |
cmurphy
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Aug 4, 2025
cmd/cosign/cli/attest/attest_blob.go
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| if c.SigningConfig != nil { | ||
| // TODO: Only ephemeral keys are currently supported |
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Discussed offline but will still note here, I think it's important to get this added quickly as it's a bigger use case in cosign than in sigstore-go.
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Created issues to track this, will get this implemented right after.
| opts.TrustedRoot = trustedMaterial | ||
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| if idToken != "" { |
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Could fetching the idToken be moved here, instead of duplicating in sign_blob.go and attest_blob.go? This is already where the rest of the SelectService logic seems to be happening.
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Refactored identity token retrieval into its own method that's now called from sign_blob and attest_blob. When we move this out into a shared library and work towards v3, I'll want to refactor this a bit more - for example, providing an identity token via flag that's either the token itself or a path isn't the cleanest UX.
This was referenced Aug 4, 2025
This will allow these functions to be reused by other parts of the codebase, and eventually we can move these into an external package for use by other libraries. Signed-off-by: Hayden B <[email protected]>
Signed-off-by: Hayden B <[email protected]>
Signed-off-by: Hayden B <[email protected]>
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steiza
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| // TODO(#4327): Only ephemeral keys are currently supported | ||
| // Need to add support for self-managed keys (e.g. PKCS11, KMS, on disk) | ||
| // and determine if we want to store certificates for those as well. |
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In the meantime, should we check for key flags like --key, --sk, or --slot and return an error to the user? Otherwise I'm worried we're silently ignoring those options if you're using signing config.
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Good idea, returning an error if any self-managed key is provided with a signing config.
Tracking this in #4324. My plan would be to merge this PR and your PR, then I'll circle back to add support for |
Signed-off-by: Hayden B <[email protected]>
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This MR contains the following updates: | Package | Update | Change | |---|---|---| | [cosign](https://github.com/sigstore/cosign) | minor | `2.5.3` -> `2.6.0` | MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot). **Proposed changes to behavior should be submitted there as MRs.** --- ### Release Notes <details> <summary>sigstore/cosign (cosign)</summary> ### [`v2.6.0`](https://github.com/sigstore/cosign/blob/HEAD/CHANGELOG.md#v260) [Compare Source](sigstore/cosign@v2.5.3...v2.6.0) v2.6.0 introduces a number of new features, including: - Signing an in-toto statement rather than Cosign constructing one from a predicate, along with verifying a statement's subject using a digest and digest algorithm rather than providing a file reference ([#​4306](sigstore/cosign#4306)) - Uploading a signature and its verification material (a ["bundle"](https://github.com/sigstore/protobuf-specs/blob/main/protos/sigstore_bundle.proto)) as an OCI Image 1.1 referring artifact, completing [#​3927](sigstore/cosign#3927) ([#​4316](sigstore/cosign#4316)) - Providing service URLs for signing and attesting using a [SigningConfig](https://github.com/sigstore/protobuf-specs/blob/4df5baadcdb582a70c2bc032e042c0a218eb3841/protos/sigstore_trustroot.proto#L185). Note that this is required when using a [Rekor v2](https://github.com/sigstore/rekor-tiles) instance ([#​4319](sigstore/cosign#4319)) Example generation and verification of a signed in-toto statement: ``` cosign attest-blob --new-bundle-format=true --bundle="digest-key-test.sigstore.json" --key="cosign.key" --statement="../sigstore-go/examples/sigstore-go-signing/intoto.txt" cosign verify-blob-attestation --bundle="digest-key-test.sigstore.json" --key=cosign.pub --type=unused --digest="b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9" --digestAlg="sha256" ``` Example container signing and verification using the new bundle format and referring artifacts: ``` cosign sign --new-bundle-format=true ghcr.io/user/alpine@sha256:a19367999603840546b8612572e338ec076c6d1f2fec61760a9e11410f546733 cosign verify --new-bundle-format=true ghcr.io/user/alpine@sha256:a19367999603840546b8612572e338ec076c6d1f2fec61760a9e11410f546733 ``` Example usage of a signing config provided by the public good instance's TUF repository: ``` cosign sign-blob --use-signing-config --bundle sigstore.json README.md cosign verify-blob --new-bundle-format --bundle sigstore.json --certificate-identity $EMAIL --certificate-oidc-issuer $ISSUER --use-signed-timestamps README.md ``` v2.6.0 leverages sigstore-go's signing and verification APIs gated behind these new flags. In an upcoming major release, we will be updating Cosign to default to producing and consuming bundles to align with all other Sigstore SDKs. #### Features - Add to `attest-blob` the ability to supply a complete in-toto statement, and add to `verify-blob-attestation` the ability to verify with just a digest ([#​4306](sigstore/cosign#4306)) - Have cosign sign support bundle format ([#​4316](sigstore/cosign#4316)) - Add support for SigningConfig for sign-blob/attest-blob, support Rekor v2 ([#​4319](sigstore/cosign#4319)) - Add support for SigningConfig in sign/attest ([#​4371](sigstore/cosign#4371)) - Support self-managed keys when signing with sigstore-go ([#​4368](sigstore/cosign#4368)) - Don't require timestamps when verifying with a key ([#​4337](sigstore/cosign#4337)) - Don't load content from TUF if trusted root path is specified ([#​4347](sigstore/cosign#4347)) - Add a terminal spinner while signing with sigstore-go ([#​4402](sigstore/cosign#4402)) - Require exclusively a SigningConfig or service URLs when signing ([#​4403](sigstore/cosign#4403)) - Remove SHA256 assumption in sign-blob/verify-blob ([#​4050](sigstore/cosign#4050)) - Bump sigstore-go, support alternative hash algorithms with keys ([#​4386](sigstore/cosign#4386)) #### Breaking API Changes - `sign.SignerFromKeyOpts` no longer generates a key. Instead, it returns whether or not the client needs to generate a key, and if so, clients should call `sign.KeylessSigner`. This allows clients to more easily manage key generation. #### Bug Fixes - Verify subject with bundle only when checking claims ([#​4320](sigstore/cosign#4320)) - Fixes to cosign sign / verify for the new bundle format ([#​4346](sigstore/cosign#4346)) </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this MR and you won't be reminded about this update again. --- - [ ] <!-- rebase-check -->If you want to rebase/retry this MR, check this box --- This MR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate). <!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0MS4xMTMuNSIsInVwZGF0ZWRJblZlciI6IjQxLjExMy41IiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6WyJSZW5vdmF0ZSBCb3QiXX0=-->
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Summary
This is the first PR to leverage sigstore-go's signing API, which is gated on whether or not a signing config is provided. While we could continue to reuse Cosign's signing APIs by passing in the signing config URLs to KeyOpts, we would not have support for Rekor v2 signing, which has only been implemented in sigstore-go. When a SigningConfig is provided, it will also force usage of the new bundle format.
You can see how much simpler sign/attest-blob will be once we start refactoring the CLI code.
There are two follow ups for this PR: Adding support for SigningConfig for attest (and eventually sign) and adding support for self-managed keys, which just requires a few Keypair implementations that wrap SignerVerifier.
This PR is split into two commits. The first refactors the authentication layer so it can be reused without Cosign's fulcio.Signer (which we can eventually move out to a utilities library), and the second adds support for SigningConfig.
Release Note
Documentation