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sigstore / Cosign⚓︎

sigstore is a Linux Foundation project that aims to provide public software signing and transparency to improve open source supply chain security. As part of the sigstore project, Cosign allows seamless container signing, verification and storage. You can read more about it here.

Connaisseur currently supports the elementary function of verifying Cosign-generated signatures based on the following types of keys:

We plan to expose further features of Cosign and sigstore in upcoming releases, so stay tuned!

Basic usage⚓︎

Getting started with Cosign is very well described in the docs. You can download Cosign from its GitHub repository. In short: After installation, a keypair is generated via:

cosign generate-key-pair

You will be prompted to set a password, after which a private (cosign.key) and public (cosign.pub) key are created. You can then use Cosign to sign a container image using:

# Here, ${IMAGE} is REPOSITORY/IMAGE_NAME:TAG
cosign sign -key cosign.key ${IMAGE}

The created signature can be verfied via:

cosign verify -key cosign.pub ${IMAGE}

To use Connaisseur with Cosign, configure a validator in helm/values.yaml with the generated public key (cosign.pub) as a trust root. The entry in .validators should look something like this (make sure to add your own public key to trust root default):

- name: customvalidator
  type: cosign
  trust_roots:
  - name: default
    key: |  # YOUR PUBLIC KEY BELOW
      -----BEGIN PUBLIC KEY-----
      MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEvtc/qpHtx7iUUj+rRHR99a8mnGni
      qiGkmUb9YpWWTS4YwlvwdmMDiGzcsHiDOYz6f88u2hCRF5GUCvyiZAKrsA==
      -----END PUBLIC KEY-----

In .policy, add a pattern to match your public key to your own repository:

- pattern: "docker.io/securesystemsengineering/testimage:co*"  # YOUR REPOSITORY
  validator: customvalidator

After installation, you are ready to verify your images against your public key:

helm install connaisseur helm --atomic --create-namespace --namespace connaisseur

A quick guide for installation and testing is available in getting started. In case you just use the default values for the validator and image policy given above, you are able to successfully validate our signed testimage:

kubectl run signed --image=docker.io/securesystemsengineering/testimage:co-signed

And compare this to the unsigned image:

kubectl run unsigned --image=docker.io/securesystemsengineering/testimage:co-unsigned

Or signed with a different key:

kubectl run altsigned --image=docker.io/securesystemsengineering/testimage:co-signed-alt

Configuration options⚓︎

.validators[*] in helm/values.yaml supports the following keys for Cosign (refer to basics for more information on default keys):

Key Default Required Description
name ✔ See basics.
type ✔ cosign; the validator type must be set to cosign.
trust_roots[*].name ✔ See basics.
trust_roots[*].key ✔ See basics. ECDSA public key from cosign.pub file or KMS URI. See additional notes below.
host Not yet implemented.
auth. Authentication credentials for private registries.
auth.secret_name Name of a Kubernetes secret in Connaisseur namespace that contains dockerconfigjson for registry authentication. See additional notes below.

Example⚓︎

validators:
- name: myvalidator
  type: cosign
  trust_roots:
  - name: mykey
    key: |
      -----BEGIN PUBLIC KEY-----
      MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEvtc/qpHtx7iUUj+rRHR99a8mnGni
      qiGkmUb9YpWWTS4YwlvwdmMDiGzcsHiDOYz6f88u2hCRF5GUCvyiZAKrsA==
      -----END PUBLIC KEY-----

policy:
- pattern: "docker.io/securesystemsengineering/testimage:co-*"
  validator: myvalidator
  with:
    key: mykey

Additional notes⚓︎

Authentication⚓︎

When using a private registry for images and signature data, the credentials need to be provided to Connaisseur. This is done by creating a dockerconfigjson Kubernetes secret in the Connaisseur namespace and passing the secret name to Connaisseur as auth.secret_name. The secret can for example be created directly from your local config.json (for docker this resides in ~/.docker/config.json):

kubectl create secret generic my-secret \
  --from-file=.dockerconfigjson=path/to/config.json \
  --type=kubernetes.io/dockerconfigjson -n connaisseur

In the above case, the secret name in Connaisseur configuration would be secret_name: my-secret. It is possible to provide one Kubernetes secret with a config.json for authentication to multiple private registries and referencing this in multiple validators.

KMS Support⚓︎

⚠ This is currently an experimental feature that might unstable over time. As such, it is not part of our semantic versioning guarantees and we take the liberty to adjust or remove it with any version at any time without incrementing MAJOR or MINOR.

Connaisseur supports Cosign's URI-based KMS integration to manage the signing and verification keys. Simply configure the trust root key value as the respective URI. In case of a Kubernetes secret, this would take the following form:

- name: myvalidator
  type: cosign
  trust_roots:
  - name: mykey
    key: k8s://connaisseur/cosignkeys

For that specific case of a Kubernetes secret, make sure to place it in a suitable namespace and grant Connaisseur access to it1.

Most other KMS will require credentials for authentication that must be provided via environment variables. Such environment variables can be injected into Connaisseur via deployment.envs in helm/values.yaml, e.g.:

  envs: 
    VAULT_ADDR: myvault.com
    VAULT_TOKEN: secrettoken

Verification against transparency log⚓︎

Connaisseur already verifies signatures against the transparency log. However, optional enforcement of transparency log is only planned in upcoming releases.

Keyless signatures⚓︎

Keyless signatures have not yet been implemented but are planned in upcoming releases.

  1. The corresponding role and rolebinding should look similar to the following: 

    apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: connaisseur-kms-role
  namespace: connaisseur  # namespace of respective k8s secret, might have to change that
  labels:
    app.kubernetes.io/name: connaisseur
rules:
- apiGroups: ["*"]
  resources: ["secrets"]
  verbs: ["get"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: connaisseur-kms-rolebinding
  namespace: connaisseur  # namespace of respective k8s secret, might have to change that
  labels:
    app.kubernetes.io/name: connaisseur
subjects:
- kind: ServiceAccount
  name: connaisseur-serviceaccount
  namespace: connaisseur  # Connaisseur's namespace, might have to change that
roleRef:
  kind: Role
  name: connaisseur-kms-role
  apiGroup: rbac.authorization.k8s.io
    Make sure to adjust it as needed. ↩

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