Signing OCI containers (and other artifacts) using Sigstore!
Cosign aims to make signatures invisible infrastructure.
Cosign supports:
- "Keyless signing" with the Sigstore public good Fulcio certificate authority and Rekor transparency log (default)
- Hardware and KMS signing
- Signing with a cosign generated encrypted private/public keypair
- Container Signing, Verification and Storage in an OCI registry.
- Bring-your-own PKI
Cosign
is developed as part of the sigstore
project.
We also use a slack channel!
Click here for the invite link.
For Homebrew, Arch, Nix, GitHub Action, and Kubernetes installs see the installation docs.
For Linux and macOS binaries see the GitHub release assets.
If you have Go 1.19+, you can setup a development environment:
$ git clone https://github.com/sigstore/cosign
$ cd cosign
$ go install ./cmd/cosign
$ $(go env GOPATH)/bin/cosign
If you are interested in contributing to cosign
, please read the contributing documentation.
Here is how to install and use cosign inside a Dockerfile through the gcr.io/projectsigstore/cosign image:
FROM gcr.io/projectsigstore/cosign:v1.13.0 as cosign-bin
# Source: https://github.com/chainguard-images/static
FROM cgr.dev/chainguard/static:latest
COPY --from=cosign-bin /ko-app/cosign /usr/local/bin/cosign
ENTRYPOINT [ "cosign" ]
This shows how to:
- sign a container image with the default "keyless signing" method (see KEYLESS.md)
- verify the container image
Note that you should always sign images based on their digest (@sha256:...
)
rather than a tag (:latest
) because otherwise you might sign something you
didn't intend to!
cosign sign $IMAGE
Generating ephemeral keys...
Retrieving signed certificate...
Note that there may be personally identifiable information associated with this signed artifact.
This may include the email address associated with the account with which you authenticate.
This information will be used for signing this artifact and will be stored in public transparency logs and cannot be removed later.
By typing 'y', you attest that you grant (or have permission to grant) and agree to have this information stored permanently in transparency logs.
Are you sure you would like to continue? [y/N] y
Your browser will now be opened to:
https://oauth2.sigstore.dev/auth/auth?access_type=online&client_id=sigstore&code_challenge=OrXitVKUZm2lEWHVt1oQWR4HZvn0rSlKhLcltglYxCY&code_challenge_method=S256&nonce=2KvOWeTFxYfxyzHtssvlIXmY6Jk&redirect_uri=http%3A%2F%2Flocalhost%3A57102%2Fauth%2Fcallback&response_type=code&scope=openid+email&state=2KvOWfbQJ1caqScgjwibzK2qJmb
Successfully verified SCT...
tlog entry created with index: 12086900
Pushing signature to: $IMAGE
Cosign will prompt you to authenticate via OIDC, where you'll sign in with your email address. Under the hood, cosign will request a code signing certificate from the Fulcio certificate authority. The subject of the certificate will match the email address you logged in with. Cosign will then store the signature and certificate in the Rekor transparency log, and upload the signature to the OCI registry alongside the image you're signing.
To verify the image, you'll need to pass in the expected certificate issuer and certificate subject via the --certificate-identity
and --certificate-oidc-issuer
flags:
cosign verify $IMAGE --certificate-identity=$IDENTITY --certificate-oidc-issuer=$OIDC_ISSUER
You can also pass in a regex for the certificate identity and issuer flags, --certificate-identity-regexp
and --certificate-oidc-issuer-regexp
.
This command returns 0
if at least one cosign
formatted signature for the image is found
matching the public key.
See the detailed usage below for information and caveats on other signature formats.
Any valid payloads are printed to stdout, in json format. Note that these signed payloads include the digest of the container image, which is how we can be sure these "detached" signatures cover the correct image.
$ cosign verify --key cosign.pub $IMAGE_URI:1h
The following checks were performed on these signatures:
- The cosign claims were validated
- The signatures were verified against the specified public key
{"Critical":{"Identity":{"docker-reference":""},"Image":{"Docker-manifest-digest":"sha256:87ef60f558bad79beea6425a3b28989f01dd417164150ab3baab98dcbf04def8"},"Type":"cosign container image signature"},"Optional":null}
While parts of cosign
are stable, we are continuing to experiment and add new features.
The following feature set is not considered stable yet, but we are committed to stabilizing it over time!
While the cosign
code for uploading, signing, retrieving, and verifying several artifact types is stable,
the format specifications for some of those types may not be considered stable yet.
Some of these are developed outside of the cosign
project, so we are waiting for them to stabilize first.
These include:
- The SBOM specification for storing SBOMs in a container registry
- The In-Toto attestation format
OCI registries are useful for storing more than just container images!
Cosign
also includes some utilities for publishing generic artifacts, including binaries, scripts, and configuration files using the OCI protocol.
This section shows how to leverage these for an easy-to-use, backwards-compatible artifact distribution system that integrates well with the rest of Sigstore.
You can publish an artifact with cosign upload blob
:
$ echo "my first artifact" > artifact
$ BLOB_SUM=$(shasum -a 256 artifact | cut -d' ' -f 1)
c69d72c98b55258f9026f984e4656f0e9fd3ef024ea3fac1d7e5c7e6249f1626 artifact
BLOB_NAME=my-artifact-(uuidgen | head -c 8 | tr 'A-Z' 'a-z')
$ BLOB_URI=ttl.sh/$BLOB_NAME:1h
$ BLOB_URI_DIGEST=$(cosign upload blob -f artifact $BLOB_URI)
Uploading file from [artifact] to [ttl.sh/my-artifact-f42c22e0:5m] with media type [text/plain]
File [artifact] is available directly at [ttl.sh/v2/my-artifact-f42c22e0/blobs/sha256:c69d72c98b55258f9026f984e4656f0e9fd3ef024ea3fac1d7e5c7e6249f1626]
Uploaded image to:
ttl.sh/my-artifact-f42c22e0@sha256:790d47850411e902aabebc3a684eeb78fcae853d4dd6e1cc554d70db7f05f99f
Your users can download it from the "direct" url with standard tools like curl or wget:
$ curl -L ttl.sh/v2/$BLOB_NAME/blobs/sha256:$BLOB_SUM > artifact-fetched
The digest is baked right into the URL, so they can check that as well:
$ cat artifact-fetched | shasum -a 256
c69d72c98b55258f9026f984e4656f0e9fd3ef024ea3fac1d7e5c7e6249f1626 -
You can sign it with the normal cosign sign
command and flags:
$ cosign sign --key cosign.key $BLOB_URI_DIGEST
Enter password for private key:
Pushing signature to: ttl.sh/my-artifact-f42c22e0
As usual, make sure to reference any images you sign by their digest to make sure you don't sign the wrong thing!
We also include the sget
command for safer, automatic verification of signatures and integration with our binary transparency log, Rekor.
To install sget
, if you have Go 1.16+, you can directly run:
$ go install github.com/sigstore/cosign/v2/cmd/sget@latest
and the resulting binary will be placed at $GOPATH/bin/sget
(or $GOBIN/sget
, if set).
Just like curl
, sget
can be used to fetch artifacts by digest using the OCI URL.
Digest verification is automatic:
$ sget us.gcr.io/dlorenc-vmtest2/readme@sha256:4aa3054270f7a70b4528f2064ee90961788e1e1518703592ae4463de3b889dec > artifact
You can also use sget
to fetch contents by tag.
Fetching contents without verifying them is dangerous, so we require the artifact be signed in this case:
$ sget gcr.io/dlorenc-vmtest2/artifact
error: public key must be specified when fetching by tag, you must fetch by digest or supply a public key
$ sget --key cosign.pub us.gcr.io/dlorenc-vmtest2/readme > foo
Verification for us.gcr.io/dlorenc-vmtest2/readme --
The following checks were performed on each of these signatures:
- The cosign claims were validated
- Existence of the claims in the transparency log was verified offline
- The signatures were verified against the specified public key
- The code-signing certificate was verified using trusted certificate authority certificates
The signature, claims and transparency log proofs are all verified automatically by sget as part of the download.
curl | bash
isn't a great idea, but sget | bash
is less-bad.
Tekton bundles can be uploaded and managed within an OCI registry.
The specification is here.
This means they can also be signed and verified with cosign
.
Tekton Bundles can currently be uploaded with the tkn cli, but we may add this support to
cosign
in the future.
$ tkn bundle push us.gcr.io/dlorenc-vmtest2/pipeline:latest -f task-output-image.yaml
Creating Tekton Bundle:
- Added TaskRun: to image
Pushed Tekton Bundle to us.gcr.io/dlorenc-vmtest2/pipeline@sha256:124e1fdee94fe5c5f902bc94da2d6e2fea243934c74e76c2368acdc8d3ac7155
$ cosign sign --key cosign.key us.gcr.io/dlorenc-vmtest2/pipeline@sha256:124e1fdee94fe5c5f902bc94da2d6e2fea243934c74e76c2368acdc8d3ac7155
Enter password for private key:
tlog entry created with index: 5086
Pushing signature to: us.gcr.io/dlorenc-vmtest2/demo:sha256-124e1fdee94fe5c5f902bc94da2d6e2fea243934c74e76c2368acdc8d3ac7155.sig
Web Assembly Modules can also be stored in an OCI registry, using this specification.
Cosign can upload these using the cosign wasm upload
command:
$ cosign upload wasm -f hello.wasm us.gcr.io/dlorenc-vmtest2/wasm
$ cosign sign --key cosign.key us.gcr.io/dlorenc-vmtest2/wasm@sha256:9e7a511fb3130ee4641baf1adc0400bed674d4afc3f1b81bb581c3c8f613f812
Enter password for private key:
tlog entry created with index: 5198
Pushing signature to: us.gcr.io/dlorenc-vmtest2/wasm:sha256-9e7a511fb3130ee4641baf1adc0400bed674d4afc3f1b81bb581c3c8f613f812.sig
eBPF modules can also be stored in an OCI registry, using this specification.
The image below was built using the bee
tool. More information can be found here
Cosign can then sign these images as they can any other OCI image.
$ bee build ./examples/tcpconnect/tcpconnect.c localhost:5000/tcpconnect:test
$ bee push localhost:5000/tcpconnect:test
$ cosign sign --key cosign.key localhost:5000/tcpconnect@sha256:7a91c50d922925f152fec96ed1d84b7bc6b2079c169d68826f6cf307f22d40e6
Enter password for private key:
Pushing signature to: localhost:5000/tcpconnect
$ cosign verify --key cosign.pub localhost:5000/tcpconnect:test
Verification for localhost:5000/tcpconnect:test --
The following checks were performed on each of these signatures:
- The cosign claims were validated
- The signatures were verified against the specified public key
[{"critical":{"identity":{"docker-reference":"localhost:5000/tcpconnect"},"image":{"docker-manifest-digest":"sha256:7a91c50d922925f152fec96ed1d84b7bc6b2079c169d68826f6cf307f22d40e6"},"type":"cosign container image signature"},"optional":null}]
Cosign also has built-in support for in-toto attestations. The specification for these is defined here.
You can create and sign one from a local predicate file using the following commands:
$ cosign attest --predicate <file> --key cosign.key $IMAGE_URI_DIGEST
All of the standard key management systems are supported. Payloads are signed using the DSSE signing spec, defined here.
To verify:
$ cosign verify-attestation --key cosign.pub $IMAGE_URI
See the Usage documentation for more commands!
See the Hardware Tokens documentation for information on how to use cosign
with hardware.
๐จ ๐จ ๐จ See here for info on the experimental Keyless signatures mode. ๐จ ๐จ ๐จ
cosign
uses go-containerregistry for registry
interactions, which has generally excellent compatibility, but some registries may have quirks.
Today, cosign
has been tested and works against the following registries:
- AWS Elastic Container Registry
- GCP's Artifact Registry and Container Registry
- Docker Hub
- Azure Container Registry
- JFrog Artifactory Container Registry
- The CNCF distribution/distribution Registry
- GitLab Container Registry
- GitHub Container Registry
- The CNCF Harbor Registry
- Digital Ocean Container Registry
- Sonatype Nexus Container Registry
- Alibaba Cloud Container Registry
- Red Hat Quay Container Registry 3.6+ / Red Hat quay.io
- Elastic Container Registry
- IBM Cloud Container Registry
- Cloudsmith Container Registry
We aim for wide registry support. To sign
images in registries which do not yet fully support OCI media types, one may need to use COSIGN_DOCKER_MEDIA_TYPES
to fall back to legacy equivalents. For example:
COSIGN_DOCKER_MEDIA_TYPES=1 cosign sign --key cosign.key legacy-registry.example.com/my/image@$DIGEST
Please help test and file bugs if you see issues! Instructions can be found in the tracking issue.
cosign
only generates ECDSA-P256 keys and uses SHA256 hashes.
Keys are stored in PEM-encoded PKCS8 format.
However, you can use cosign
to store and retrieve signatures in any format, from any algorithm.
cosign
will integrate with transparency logs!
See sigstore#34 for more info.
cosign
will integrate with even more transparency logs, and a PKI.
See https://github.com/sigStore/fulcio for more info.
cosign
will also support The Update Framework for delegations, key discovery and expiration.
See sigstore#86 for more info!
cosign
only supports Red Hat's simple signing
format for payloads.
That looks like:
{
"critical": {
"identity": {
"docker-reference": "testing/manifest"
},
"image": {
"Docker-manifest-digest": "sha256:20be...fe55"
},
"type": "cosign container image signature"
},
"optional": {
"creator": "Bob the Builder",
"timestamp": 1458239713
}
}
Note: This can be generated for an image reference using cosign generate $IMAGE_URI_DIGEST
.
I'm happy to switch this format to something else if it makes sense. See notaryproject/notation#40 for one option.
cosign
signatures are stored as separate objects in the OCI registry, with only a weak
reference back to the object they "sign".
This means this relationship is opaque to the registry, and signatures will not be deleted
or garbage-collected when the image is deleted.
Similarly, they can easily be copied from one environment to another, but this is not
automatic.
Multiple signatures are stored in a list which is unfortunately a race condition today. To add a signature, clients orchestrate a "read-append-write" operation, so the last write will win in the case of contention.
cosign
will default to storing signatures in the same repo as the image it is signing.
To specify a different repo for signatures, you can set the COSIGN_REPOSITORY
environment variable.
This will replace the repo in the provided image like this:
$ export COSIGN_REPOSITORY=gcr.io/my-new-repo
$ cosign sign --key cosign.key $IMAGE_URI_DIGEST
So the signature for gcr.io/dlorenc-vmtest2/demo
will be stored in gcr.io/my-new-repo/demo:sha256-DIGEST.sig
.
Note: different registries might expect different formats for the "repository."
-
To use GCR, a registry name like
gcr.io/$REPO
is sufficient, as in the example above. -
To use Artifact Registry, specify a full image name like
$LOCATION-docker.pkg.dev/$PROJECT/$REPO/$STORAGE_IMAGE
, not just a repository. For example,$ export COSIGN_REPOSITORY=us-docker.pkg.dev/my-new-repo/demo $ cosign sign --key cosign.key $IMAGE_URI_DIGEST
where the
sha256-DIGEST
will match the digest forgcr.io/dlorenc-vmtest2/demo
. Specifying just a repo like$LOCATION-docker.pkg.dev/$PROJECT/$REPO
will not work in Artifact Registry.
cosign
is inspired by tools like minisign and
signify.
Generated private keys are stored in PEM format. The keys encrypted under a password using scrypt as a KDF and nacl/secretbox for encryption.
They have a PEM header of ENCRYPTED SIGSTORE PRIVATE KEY
:
-----BEGIN ENCRYPTED SIGSTORE PRIVATE KEY-----
...
-----END ENCRYPTED SIGSTORE PRIVATE KEY-----
Public keys are stored on disk in PEM-encoded standard PKIX format with a header of PUBLIC KEY
.
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAELigCnlLNKgOglRTx1D7JhI7eRw99
QolE9Jo4QUxnbMy5nUuBL+UZF9qqfm/Dg1BNeHRThHzWh2ki9vAEgWEDOw==
-----END PUBLIC KEY-----
cosign
stores signatures in an OCI registry, and uses a naming convention (tag based
on the sha256 of what we're signing) for locating the signature index.
reg.example.com/ubuntu@sha256:703218c0465075f4425e58fac086e09e1de5c340b12976ab9eb8ad26615c3715
has signatures located at reg.example.com/ubuntu:sha256-703218c0465075f4425e58fac086e09e1de5c340b12976ab9eb8ad26615c3715.sig
Roughly (ignoring ports in the hostname): s/:/-/g
and s/@/:/g
to find the signature index.
See Race conditions for some caveats around this strategy.
Alternative implementations could use transparency logs, local filesystem, a separate repository registry, an explicit reference to a signature index, a new registry API, grafeas, etc.
cosign
only works for artifacts stored as "manifests" in the registry today.
The proposed mechanism is flexible enough to support signing arbitrary things.
cosign
supports using a KMS provider to generate and sign keys.
Right now cosign supports Hashicorp Vault, AWS KMS, GCP KMS, Azure Key Vault and we are hoping to support more in the future!
See the KMS docs for more details.
Push an artifact to a registry using oras (in this case, cosign
itself!):
$ oras push us-central1-docker.pkg.dev/dlorenc-vmtest2/test/artifact ./cosign
Uploading f53604826795 cosign
Pushed us-central1-docker.pkg.dev/dlorenc-vmtest2/test/artifact
Digest: sha256:551e6cce7ed2e5c914998f931b277bc879e675b74843e6f29bc17f3b5f692bef
Now sign it! Using cosign
of course:
$ cosign sign --key cosign.key us-central1-docker.pkg.dev/dlorenc-vmtest2/test/artifact@sha256:551e6cce7ed2e5c914998f931b277bc879e675b74843e6f29bc17f3b5f692bef
Enter password for private key:
Pushing signature to: us-central1-docker.pkg.dev/dlorenc-vmtest2/test/artifact:sha256-551e6cce7ed2e5c914998f931b277bc879e675b74843e6f29bc17f3b5f692bef.sig
Finally, verify cosign
with cosign
again:
$ cosign verify --key cosign.pub us-central1-docker.pkg.dev/dlorenc-vmtest2/test/artifact@sha256:551e6cce7ed2e5c914998f931b277bc879e675b74843e6f29bc17f3b5f692bef
The following checks were performed on each of these signatures:
- The cosign claims were validated
- The claims were present in the transparency log
- The signatures were integrated into the transparency log when the certificate was valid
- The signatures were verified against the specified public key
- The code-signing certificate was verified using trusted certificate authority certificates
{"Critical":{"Identity":{"docker-reference":""},"Image":{"Docker-manifest-digest":"sha256:551e6cce7ed2e5c914998f931b277bc879e675b74843e6f29bc17f3b5f692bef"},"Type":"cosign container image signature"},"Optional":null}
It's hard to answer this briefly. This post contains some comparisons:
If you find other comparison posts, please send a PR here and we'll link them all.
containers/image
signing is close to cosign
, and we reuse payload formats.
cosign
differs in that it signs with ECDSA-P256 keys instead of PGP, and stores
signatures in the registry.
I believe this tool is complementary to TUF, and they can be used together. I haven't tried yet, but think we can also reuse a registry for TUF storage.
Just kidding. Nobody actually asked this. Don't be that person.
See the next section, Requirements. I designed this tool to meet a few specific requirements, and didn't find anything else that met all of these. If you're aware of another system that does meet these, please let me know!
- No external services for signature storage, querying, or retrieval
- We aim for as much registry support as possible
- Everything should work over the registry API
- PGP should not be required at all.
- Users must be able to find all signatures for an image
- Signers can sign an image after push
- Multiple entities can sign an image
- Signing an image does not mutate the image
- Pure-go implementation
The naming convention and read-modify-write update patterns we use to store things in a registry are a bit, well, "hacky". I think they're the best (only) real option available today, but if the registry API changes we can improve these.
cosign
can sign anything in a registry.
These examples show signing a single image, but you could also sign a multi-platform Index
,
or any other type of artifact.
This includes Helm Charts, Tekton Pipelines, and anything else currently using OCI registries
for distribution.
This also means new artifact types can be uploaded to a registry and signed. One interesting type to store and sign would be TUF repositories. I haven't tried yet, but I'm fairly certain TUF could be implemented on top of this.
cosign
signatures protect the digests of objects stored in a registry.
The optional annotations
support (via the -a
flag to cosign sign
) can be used to add extra
data to the payload that is signed and protected by the signature.
One use-case for this might be to sign a tag->digest mapping.
If you would like to attest that a specific tag (or set of tags) should point at a digest, you can run something like:
$ docker push $IMAGE_URI
The push refers to repository [dlorenc/demo]
994393dc58e7: Pushed
5m: digest: sha256:1304f174557314a7ed9eddb4eab12fed12cb0cd9809e4c28f29af86979a3c870 size: 528
$ TAG=sign-me
$ cosign sign --key cosign.key -a tag=$TAG $IMAGE_URI_DIGEST
Enter password for private key:
Pushing signature to: dlorenc/demo:1304f174557314a7ed9eddb4eab12fed12cb0cd9809e4c28f29af86979a3c870.sig
Then you can verify that the tag->digest mapping is also covered in the signature, using the -a
flag to cosign verify
.
This example verifies that the digest $TAG
which points to (sha256:1304f174557314a7ed9eddb4eab12fed12cb0cd9809e4c28f29af86979a3c870
)
has been signed, and also that the tag
annotation has the value sign-me
:
$ cosign verify --key cosign.pub -a tag=$TAG $IMAGE_URI | jq .
{
"Critical": {
"Identity": {
"docker-reference": ""
},
"Image": {
"Docker-manifest-digest": "97fc222cee7991b5b061d4d4afdb5f3428fcb0c9054e1690313786befa1e4e36"
},
"Type": "cosign container image signature"
},
"Optional": {
"tag": "sign-me"
}
}
Timestamps could also be added here, to implement TUF-style freeze-attack prevention.
Again, cosign
can sign anything in a registry.
You could use cosign
to sign an image that is intended to be used as a base image,
and include that provenance metadata in resulting derived images.
This could be used to enforce that an image was built from an authorized base image.
Rough Idea:
- OCI manifests have an ordered list of
layer
Descriptors
, which can contain annotations. See here for the specification. - A base image is an ordered list of layers to which other layers are appended, as well as an
initial configuration object that is mutated.
- A derived image is free to completely delete/destroy/recreate the config from its base image, so signing the config would provided limited value.
- We can sign the full set of ordered base layers, and attach that signature as an annotation to the last layer in the resulting child image.
This example manifest manifest represents an image that has been built from a base image with two layers. One additional layer is added, forming the final image.
{
"schemaVersion": 2,
"config": {
"mediaType": "application/vnd.oci.image.config.v1+json",
"size": 7023,
"digest": "sha256:b5b2b2c507a0944348e0303114d8d93aaaa081732b86451d9bce1f432a537bc7"
},
"layers": [
{
"mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
"size": 32654,
"digest": "sha256:9834876dcfb05cb167a5c24953eba58c4ac89b1adf57f28f2f9d09af107ee8f0"
},
{
"mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
"size": 16724,
"digest": "sha256:3c3a4604a545cdc127456d94e421cd355bca5b528f4a9c1905b15da2eb4a4c6b",
"annotations": {
"dev.cosign.signature.baseimage": "Ejy6ipGJjUzMDoQFePWixqPBYF0iSnIvpMWps3mlcYNSEcRRZelL7GzimKXaMjxfhy5bshNGvDT5QoUJ0tqUAg=="
}
},
{
"mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
"size": 73109,
"digest": "sha256:ec4b8955958665577945c89419d1af06b5f7636b4ac3da7f12184802ad867736"
}
],
}
Note that this could be applied recursively, for multiple intermediate base images.
Cosign signatures (and their protected payloads) are stored as artifacts in a registry. These signature objects can also be signed, resulting in a new, "counter-signature" artifact. This "counter-signature" protects the signature (or set of signatures) and the referenced artifact, which allows it to act as an attestation to the signature(s) themselves.
Before we sign the signature artifact, we first give it a memorable name so we can find it later.
$ cosign sign --key cosign.key -a sig=original $IMAGE_URI_DIGEST
Enter password for private key:
Pushing signature to: dlorenc/demo:sha256-97fc222cee7991b5b061d4d4afdb5f3428fcb0c9054e1690313786befa1e4e36.sig
$ cosign verify --key cosign.pub dlorenc/demo | jq .
{
"Critical": {
"Identity": {
"docker-reference": ""
},
"Image": {
"Docker-manifest-digest": "97fc222cee7991b5b061d4d4afdb5f3428fcb0c9054e1690313786befa1e4e36"
},
"Type": "cosign container image signature"
},
"Optional": {
"sig": "original"
}
}
Now give that signature a memorable name, then sign that:
$ crane tag $(cosign triangulate $IMAGE_URI) mysignature
2021/02/15 20:22:55 dlorenc/demo:mysignature: digest: sha256:71f70e5d29bde87f988740665257c35b1c6f52dafa20fab4ba16b3b1f4c6ba0e size: 556
$ cosign sign --key cosign.key -a sig=counter dlorenc/demo:mysignature
Enter password for private key:
Pushing signature to: dlorenc/demo:sha256-71f70e5d29bde87f988740665257c35b1c6f52dafa20fab4ba16b3b1f4c6ba0e.sig
$ cosign verify --key cosign.pub dlorenc/demo:mysignature
{"Critical":{"Identity":{"docker-reference":""},"Image":{"Docker-manifest-digest":"71f70e5d29bde87f988740665257c35b1c6f52dafa20fab4ba16b3b1f4c6ba0e"},"Type":"cosign container image signature"},"Optional":{"sig":"counter"}}
Finally, check the original signature:
$ crane manifest dlorenc/demo@sha256:71f70e5d29bde87f988740665257c35b1c6f52dafa20fab4ba16b3b1f4c6ba0e
{
"schemaVersion": 2,
"config": {
"mediaType": "application/vnd.oci.image.config.v1+json",
"size": 233,
"digest": "sha256:3b25a088710d03f39be26629d22eb68cd277a01673b9cb461c4c24fbf8c81c89"
},
"layers": [
{
"mediaType": "application/vnd.oci.descriptor.v1+json",
"size": 217,
"digest": "sha256:0e79a356609f038089088ec46fd95f4649d04de989487220b1a0adbcc63fadae",
"annotations": {
"dev.sigstore.cosign/signature": "5uNZKEP9rm8zxAL0VVX7McMmyArzLqtxMTNPjPO2ns+5GJpBeXg+i9ILU+WjmGAKBCqiexTxzLC1/nkOzD4cDA=="
}
}
]
}
We are intending to move to a monthly cadence for minor releases. Minor releases will be published around the beginning of the month. We may cut a patch release instead, if the changes are small enough not to warrant a minor release. We will also cut patch releases periodically as needed to address bugs.
Should you discover any security issues, please refer to sigstore's security process
The GitHub release assets for cosign contain a PEM file produced by GoReleaser while signing the cosign blob that is used to verify the integrity of the release binaries. This file is not used by cosign itself, but is provided for users who wish to verify the integrity of the release binaries.
By default, cosign output these PEM files in base64 encoded format, this approach might be good for air-gapped environments where the PEM file is stored in a file system. So, you should decode these PEM files before using them to verify the blobs.