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
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
Please help test and file bugs if you see issues! Instructions can be found in the tracking issue.
Note: this is an experimental feature
To publish signed artifacts to a Rekor transparency log and verify their existence in the log
COSIGN_EXPERIMENTAL=1 environment variable.
COSIGN_EXPERIMENTAL=1 cosign sign --key cosign.key user/demo COSIGN_EXPERIMENTAL=1 cosign verify --key cosign.pub user/demo
Cosign defaults to using the public instance of rekor at rekor.sigstore.dev.
To configure the rekor server, use the -
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 “racy” 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:
export COSIGN_REPOSITORY=gcr.io/my-new-repo gcr.io/user-vmtest2/demo -> gcr.io/my-new-repo/demo:sha256-DIGEST.sig
So the signature for
gcr.io/user-vmtest2/demo will be stored in