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

steiza · 2025-07-24T14:28:37Z

Summary

Cosign was previously very opinionated about what kinds of in-toto statements it attests, and would only verify an attestation if you provided a path to the attested file.

There's a number of community issues created due to these constraints:

Update supported in-toto Statement version to v1 #4238
- This change allows people to supply an in-toto v1 statement to cosign attest-blob via --statement
Support signing 'raw' in-toto statements #4019 and Cosign support for SLSA Source Track #4210
- People want to be able to use cosign to create and verify the upcoming SLSA Source attestations, as well as other cases where an in-toto statement might reference something other than a file on disk.

To test this PR, I did things like:

# Attesting a blob in the "old" way
$ go run cmd/cosign/main.go attest-blob --identity-token="..." --new-bundle-format=true --bundle="digest-test.sigstore.json" --type=something --predicate="../sigstore-go/examples/sigstore-go-signing/intoto.txt" ../sigstore-go/examples/sigstore-go-signing/hello_world.txt

# Verify "old" attest-blob can be verified the new way
$ go run cmd/cosign/main.go verify-blob-attestation --bundle="digest-test.sigstore.json" --certificate-oidc-issuer="https://token.actions.githubusercontent.com" --certificate-identity="https://github.com/sigstore-conformance/extremely-dangerous-public-oidc-beacon/.github/workflows/extremely-dangerous-oidc-beacon.yml@refs/heads/main" --type=something --digest="b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9" --digestAlg="sha256"

# Attest a blob just by providing a statement (and using a key instead of keyless flow)
$ go run cmd/cosign/main.go attest-blob --new-bundle-format=true --bundle="digest-key-test.sigstore.json" --key="cosign.key" --statement="../sigstore-go/examples/sigstore-go-signing/intoto.txt"

# Verify the new way; testing both attesting with just a statement (as well as the key flow instead of keyless)
$ go run cmd/cosign/main.go verify-blob-attestation --bundle="digest-key-test.sigstore.json" --key=cosign.pub --type=something --digest="b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9" --digestAlg="sha256"

Release Note

attest-blob modified to accept a full in-toto statement with --statement (use instead of --predicate, --type, and providing a path to a blob)
verify-blob-attestation modified to accept --digest and --digestAlg that correspond to the subject of your in-toto statement (use instead of providing a path to a blob)

Documentation

I ran make docgen to include cosign documentation updates in the pull request

Signed-off-by: Cody Soyland <[email protected]>

Signed-off-by: Zach Steindler <[email protected]>

codecov · 2025-07-24T14:30:31Z

Codecov Report

❌ Patch coverage is 39.49580% with 72 lines in your changes missing coverage. Please review.
✅ Project coverage is 35.03%. Comparing base (2ef6022) to head (877b6f2).
⚠️ Report is 448 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/cosign/cli/attest/attest_blob.go	44.82%	21 Missing and 11 partials ⚠️
cmd/cosign/cli/verify/verify_blob_attestation.go	58.33%	10 Missing and 5 partials ⚠️
cmd/cosign/cli/attest_blob.go	0.00%	9 Missing ⚠️
cmd/cosign/cli/options/verify.go	0.00%	7 Missing ⚠️
cmd/cosign/cli/options/predicate.go	0.00%	5 Missing ⚠️
cmd/cosign/cli/verify.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4306      +/-   ##
==========================================
- Coverage   40.10%   35.03%   -5.08%     
==========================================
  Files         155      214      +59     
  Lines       10044    14621    +4577     
==========================================
+ Hits         4028     5122    +1094     
- Misses       5530     8840    +3310     
- Partials      486      659     +173

☔ View full report in Codecov by Sentry.
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Signed-off-by: Zach Steindler <[email protected]>

haydentherapper

This is fantastic, thanks for getting this in and thank you Cody for getting this started! Just a few small remarks.

haydentherapper · 2025-07-25T18:20:04Z

cmd/cosign/cli/attest/attest_blob.go

-	payload, err := json.Marshal(sh)
-	if err != nil {
-		return err
+	fmt.Println("Using statement from:", c.StatementPath)


duplicated println with 117

haydentherapper · 2025-07-25T18:21:49Z

cmd/cosign/cli/attest/attest_blob.go

 }
+
+func validateStatement(payload []byte) (string, error) {
+	var statement *in_toto.Statement


This is noted as deprecated - https://github.com/in-toto/in-toto-golang/blob/201dc1160c44793371028e186e808467464bd44e/in_toto/attestations.go#L63

Should we use the generated Go code in https://github.com/in-toto/attestation/tree/main/go/v1 instead?

haydentherapper · 2025-07-25T18:23:28Z

cmd/cosign/cli/attest/attest_blob.go

+
+	if c.StatementPath != "" {
+		fmt.Fprintln(os.Stderr, "Using statement from:", c.StatementPath)
+		statement, err := predicateReader(c.StatementPath)


predicateReader has some output specific to predicates rather than statements, can we make this generic, or just read the file, I don't think predicateReader is needed.

haydentherapper · 2025-07-25T18:26:23Z

Is there also an e2e test we can add to e2e_test.go for generation and verification?

haydentherapper · 2025-07-25T18:28:55Z

Also, can we create an issue to track figuring out --attest with custom predicates (so we can close out some of the open issues and have a more tightly scoped one)?

Also minor fixes from code review. Signed-off-by: Zach Steindler <[email protected]>

steiza · 2025-07-25T20:17:24Z

Also, can we create an issue to track figuring out --attest with custom predicates (so we can close out some of the open issues and have a more tightly scoped one)?

Sure, I have made #4308.

haydentherapper

Fantastic!!

wolfv · 2025-09-04T15:06:31Z

When is this going to be released?

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. --- - [ ] If you want to rebase/retry this MR, check this box --- This MR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).

codysoyland and others added 3 commits July 23, 2025 16:11

Add support for attesting with complete statement

3c9ffef

Signed-off-by: Cody Soyland <[email protected]>

Back out changes to cosign attest

8f2f099

Signed-off-by: Zach Steindler <[email protected]>

Add digest support to verify-blob-attestation

2d42498

Signed-off-by: Zach Steindler <[email protected]>

steiza requested a review from a team as a code owner July 24, 2025 14:28

steiza mentioned this pull request Jul 24, 2025

Add support for attesting with complete statement #4032

Closed

steiza added 2 commits July 24, 2025 10:34

Add tests and linter fix

2b9e5ec

Signed-off-by: Zach Steindler <[email protected]>

Update make lint to match version run by GitHub Action

69e0cc8

Signed-off-by: Zach Steindler <[email protected]>

haydentherapper reviewed Jul 25, 2025

View reviewed changes

Add end-to-end test for attesting and verifying entire intoto statement

877b6f2

Also minor fixes from code review. Signed-off-by: Zach Steindler <[email protected]>

steiza requested a review from a team as a code owner July 25, 2025 20:05

steiza mentioned this pull request Jul 25, 2025

Figure out what to do with in-toto statements for cosign attest #4308

Open

haydentherapper approved these changes Jul 25, 2025

View reviewed changes

steiza merged commit fc4b1a2 into sigstore:main Jul 25, 2025
29 checks passed

steiza deleted the attest-intoto branch October 6, 2025 14:34

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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

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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

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steiza commented Jul 24, 2025

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Documentation

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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

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

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