An image is a package containing all necessary files and dependencies for running a service or application, such as an Apache server. These images, typically obtained from a container registry like Docker Hub or Google Container Registry, are digitally signed with a private key. This process involves hashing the image data and encrypting it with a secret key to produce a digital signature, providing the image with a verifiable identity.
Image verification involves examining this digital signature to ensure the image originated from a valid source and remained unaltered post-signing. This is achieved by comparing the image’s actual hash with its decoded hash; if they match, the image is deemed trustworthy and secure. This is crucial as images form the basis for deploying applications and services within a cluster. Ensuring their integrity helps prevent potential security breaches and protect sensitive data, as a compromised image or any of its components could pose significant risks.
Additionally, checking the accuracy of images may help in finding any unauthorized modifications done to the image during transfer or storage. By doing so, it will be easier to spot any security lapses or attacks and will be possible to act quickly to minimize any harm. Thus, image verification is essential in maintaining Kubernetes security.
How to Implement Image Signing and Verification?
Checking the integrity of Kubernetes images is an important security step that can help stop security breaches and protect sensitive data. By making sure that only trusted and secure images are used in the cluster, organizations can reduce the risk of security issues and protect the integrity and privacy of their data.
Let’s figure out how to implement image signing and verification.
Image signing can be implemented using the Docker Content Trust. In order to implement this you need to enable it. In order to enable it on Docker client, set the DOCKER_CONTENT_TRUST environment variable to “1”:
export DOCKER_CONTENT_TRUST=1
Once done, On your Docker registry, set the DOCKER_CONTENT_TRUST_SERVER environment variable to the URL of the notary server:
export DOCKER_CONTENT_TRUST_SERVER=https://notary.example.com
Now, the Docker Content Trust is ready and image singing is needed to be implemented using the private key and CA certificate.
Hence, generate a private key with root CA certificate using the docker trust. Run this command to generate the key as well as the CA certificate.
docker trust key generate org/root-ca
Once done load the private key in local key stores using the below command.
docker trust key load my-org/root-ca.key
After the keys have been loaded, publish the CA certificate to your registry.
docker trust signer add --key my-org/root-ca.pub my-org my-registry.com
So the image signing environment is now set, you just need to sign the images and implement the verification of them. Use this command to sign and image for the specific repository and tag.
docker push my-org/my-image:my-tag
Once signed you can push the images to the registry and can implement the signing verification. Once done, you can easily perform the image singing verification using this command.
docker trust verify my-org/my-image:my-tag
Best Practices for Managing and Distributing Signed Images
Once images are signed, doesn’t mean that all the images are secure. Since there are different things such as private keys as well as CA certificates involved, there is a lot of management that needs to be done in managing the signed images. Let’s discuss them properly.
Always Use a Private Registry
A private registry is similar to having a simple private location which can be used to save all securely signed images. It is usually recommended to utilize a private registry rather than a public one, since this will protect the privacy and security of any images that have been signed digitally. When you use the private registry, you will have control over the images that are saved in it, and you will be able to push or update the images according to your preferences. As a result, maintaining a private registry rather than a public one is the advice that should always be followed.
Rotate Keys Regularly
A private key is being used to sign the images that are now being managed. These private keys may be kept in a variety of locations, including the repository itself or the Secrets manager hosted on the cloud. It is crucial to rotate the signing keys on a regular basis in order to assist reduce the danger of a compromised key being used to sign harmful images that could be deployed within the organization. This is necessary in order to ensure that signed images can be managed and signed in a safe manner.
Use Image Vulnerability Scanning
The vulnerability scanning that goes all the way through the images can be implemented by organizations. Before an image was allowed to be pushed to a cluster or container, it went through this image vulnerability scanner to ensure that it was secure. Therefore, it is vital to implement vulnerability scanning in order to discover any vulnerabilities in the image before deployment. This will help in detecting any malicious images that may have been deployed inadvertently.
Conclusion
There are a lot of security best practices that can be applied within the kubernetes cluster. Image singing and verification can be used to verify the image that has been deployed. Using a private key, image signing involves creating a digital signature for a container image. The image’s digital signature, which is specific to it, can be used to later confirm the image’s legitimacy.
Organizations can defend their environment from potential security vulnerabilities which can occur due to modified container images or its dependencies by adopting image signing and verification in Kubernetes. It is easy to implement, can lead to great security measures and might protect the organizations from supply chain attacks as well.