Signing Images

Signing container images is a process that ensures their authenticity and integrity. This is achieved by adding a digital signature to the container image, which can be validated during deployment. The signature helps to verify that the image is from a trusted publisher and has not been modified.

Notation is an open-source supply chain tool developed by the Notary Project, which supports signing and verifying container images and other artifacts.

The following registries are compatible with the Notary Project OCI signature specification and its implementation in Notation:

  • Azure Container Registry
  • Amazon Elastic Container Registry
  • GitHub Container Registry
  • ORAS Distribution Registry
  • Zot registry

Akeyless can be used to store certificates with signing keys that can be used by Notation with the Akeyless plugin for Notation, to sign and verify container images and other artifacts for the supported container registries.

Install the Notation CLI

To install the Notation CLI, follow the relevant doc according to your environment OS as described in the Notation official docs. In the following example for simplicity, we will use Homebrew package manager.

brew install notation

Akeyless Plugin Installation

The plugin directory varies depending on the operating system being used. The directory path in our example assumes Ubuntu. Please read the Notation directory structure for system configuration for more information.

Create a folder for the Akeyless Notation plugin configuration:

mkdir -p ~/.config/notation/plugins/akeyless
mkdir $HOME/Library/Application Support/notation/plugins
mkdir %AppData%/notation/plugins

Download the Akeyless official Notation plugin for Akeyless public artifacts:

cd ~/.config/notation/plugins/akeyless
curl -o notation-akeyless https://rest.akeyless.io/Akeyless_Artifacts/Linux/notation-akeyless/notation-akeyless-linux-amd64
chmod +x notation-akeyless
cd $HOME/Library/Application Support/notation/plugins
curl https://rest.akeyless.io/Akeyless_Artifacts/MacOS/notation-akeyless/notation-akeyless-darwin-amd64
cd  %AppData%/notation/plugins
curl https://rest.akeyless.io/Akeyless_Artifacts/Windows/notation-akeyless/notation-akeyless-windows-amd64.exe

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Note

For ARM architecture download the relevant binaries from here

List the Notation Plugins list to verify that Akeyless is listed.

notation plugin ls

Configuration

Notation Plugins configuration supports the use of environment variables or static config file, our example will use a config file.

Depending on your OS type create the relevant config file accordingly:

cd /var/akeyless/conf
cat <<EOF > notation.conf
akeyless_url="https://<Your Gateway URL>:8081"
[auth]
access_id="<AccessID>"
access_key="<AccessKey>"
access_type="access_key"
EOF
cd C:\Users\<USER>\.akeyless\profiles
echo akeyless_url="https://<Your Gateway URL>:8081" > notation.conf
echo [auth] >> notation.conf
echo access_id="<AccessID>" >> notation.conf
echo access_key="<AccessKey>" >> notation.conf
echo access_type="access_key" >> notation.conf

Where:

  • akeyless_url - Your Akeyless Gateway API v2 endpoint (port 8081), if not set, by default will work with Akeyless public API endpoint https://api.akeyless.io.

  • access_type - The Authentication Method type, supporting:access_key,aws_iam,gcp,azure_ad certificate,jwt and k8s.

  • access_id - The Auth method Access ID.

  • access_key - Relevant only for API Key Auth method.

  • k8s_conf_name - Relevant only for Kubernetes Auth method.

Create a Self-Signed Certificate

The Notary project specified the requirements for different types of certificates, the following examples will use a Self Signed CA certificate.

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Note

It is possible to work with Akeyless PKI Issuer to generate the certificates, the PKI Issuer must be set with the Code Signing flag , and Key Usage List of critical,DigitalSignature.

Akeyless Supports both EC and RSA algorithms, run the following commands to create a key with a self signed certificate.

Create a CSR config file:

cat <<EOF > csr.conf
countryName				= US
stateOrProvinceName		= NY
localityName			= NY
organizationName        = Akeyless
organizationalUnitName	= Security
commonName				= akeylessSign

[ v3_req ]
basicConstraints        = critical, CA:FALSE
keyUsage                = critical, digitalSignature
EOF

Create a key with a self-signed certificate:

akeyless create-dfc-key -n CodeSign -a RSA2048 --generate-self-signed-certificate true --conf-file-path csr.conf --certificate-ttl 30

Set Notation Default Key

notation key add  --plugin akeyless  --id /CodeSign --default Akeyless

Where:

  • id- The full key name or the key item id, as stored inside Akeyless. In our example, we used the created key named CodeSign.

  • default - Optional, to mark this key for Notation as a default key, with a friendly name for notation, in this example, we simply named itAkeyless.

Verify that the key is added to the Notation keys:

notation key ls

Sign Image

For the simplicity of this example, the following steps will demonstrate the simple creation of a trust policy to sign docker artifacts.

docker run -d -p 5001:5000 ghcr.io/oras-project/registry:v1.0.0-rc.4

Use docker build and docker push to build and push a sample image to your registry.

docker build -t localhost:5001/net-monitor:v1 https://github.com/wabbit-networks/net-monitor.git#main
docker push localhost:5001/net-monitor:v1
IMAGE=$(docker inspect --format='{{index .RepoDigests 0}}' localhost:5001/net-monitor:v1)

Use notation ls to list the current signatures for your image. The following example sets the value of $IMAGE to the name of the image and its digest value.

notation ls $IMAGE

Confirm there are no signatures listed. And use notation sign command to sign the image:

notation sign $IMAGE

Verify Image Signatures

To verify the container image, add the root certificate that signs the leaf certificate to the trust store and create trust policies for verification. For the self-signed certificate used in this tutorial, the root certificate is the self-signed certificate itself.

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Note

Depending on your OS the follow the folder structure as described here

Get the certificate from Akeyless:

 akeyless describe-item -n CodeSign --json --jq-expression .certificates >> certificate.pem

Add the public certificate to a named trust store for signature verification:

notation certificate add --type ca --store selfSigned certificate.pem 

Create a trustpolicy.json with the following trust policy in the notation configuration directory.

Note: this is a very permissive trust policy. Read more on creating trust policies and trust stores here:

{
 "version": "1.0",
 "trustPolicies": [
     {
         "name": "trust-policy-example",
         "registryScopes": [ "*" ],
         "signatureVerification": {
             "level" : "strict" 
         },
         "trustStores": [ "ca:selfSigned" ],
         "trustedIdentities": [
             "*"
         ]
     }
 ]
}

Add the policy to notation

notation policy import trustpolicy.json

Verify the signature

notation verify $IMAGE