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How to Use Docker Content Trust to Verify Docker Container Images

Last Updated : 19 Jan, 2024
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The world of containerized applications is based on trust. You rely on Docker images to be exactly what they say they are: secure, reliable, robust, and built with the right elements. But just like you can not just blindly trust any random ingredient in your kitchen, similarly the Docker image needs a kind of verification so we don’t need to be concerned about security issues.

DCT is an essential feature for your Docker container security. It allows you to focus on building and deploying amazing applications, while it takes care of the critical tasks of ensuring security.

Benefits of DCT

  • DCT verifies the publisher of your images, so you know exactly who builds them and if is it safe or not.
  • With DCT, you can confidently deploy your docker images, because you know they’re genuine and free from any kind of malicious modifications.
  • it enhances security by Protecting your systems from compromised or tampered images with a robust verification system.
  • Secure your entire container ecosystem, from individual images to complex deployments.
  • and you don’t need to concern about security and you can deploy with confidence, knowing your images are exactly what you expect them to be.

What is Docker Content Trust (DCT)?

Docker content trust (DCT) is a security functionality provided by the Docker. it verifies the authenticity of Docker images by using some security concern techniques like cryptography keys. It lowers the possibility of harmful or unauthorized alterations to the container images. and DCT makes sure that they come from an authorized source and have not been altered and it also enhances the security within the containerized environments. DCT keys play an important role for enhancing the security.

Beginner friendly example

we can understand the need for DCT and how it works with this Example: Imagine that you are making a delicious cake You carefully measure all the ingredients and you are ensuring everything is fresh and perfectly arranged. But what if someone exchange the flour for sawdust? Your cake would be ruined! That’s like a bad guy trying to mess with your software in a container. and you want to protect your Docker image from these unauthorized activities so here the DCT comes.

The Docker Content Trust (DCT) is like a trusted chef. It checks every ingredient like a professional chef who is concerned about their recipes similarly DCT is works as a gatekeeper and checks whether the person who is using the Docker image is authorized or not. it enhances the overall security of an image and gives more confidence about the image source.

How does Docker Content Trust (DCT) work?

The basic idea behind the DCT is cryptographic key technique used as a main component behind the Docker Content Trust (DCT). and it guarantees the Docker container images’ security integrity. and confirm that the pictures originate from a trustable source. since each image is given a distinct key that is supplied by trusted authorities. We are aware that each locker can only be unlocked with a special key, similarly The key serves as a signer, and you cannot pull or utilize an image without it. without the key you can not pull or use an image.

The DCT user generates a pair of cryptographic keys, one is used for the signing and the other one is used for the verification processes and the other for the public key that corresponds to it. because of these security feature clients feels more secure and they can rely on it.

The first stage in this process is image signing after that the private key is used by the repository owner or image signer to further creates an unique cryptographic code for your Docker image. This signature acts as a digital fingerprint which provide an unique identity to an image. and it offers a safe and authentic identification that enhance the security of an docker picture. The associated public key, which originates from the private key when the image is signed, is crucial for signature verification by Docker clients when retrieving or using images.

The signature is verified by clients (user of Docker image) by comparing it to the image’s content and making sure it has not been compromised by malicious activity since the signing procedure. This verification method is reliable and trustworthy. giving users the assurance that the image is authentic, that it comes from a reputable and authentic source, and that it hasn’t been altered over its whole lifecycle. Digital signatures can be used for data delivered to and received from remote Docker registries thanks to Docker Content Trust (DCT).

Docker Content Trust Keys

Trust is essential to the thriving world of containerized applications. we can not easily trust on any image because it results further causes like malicious attacks and the authenticity of each extracted image is still unclear. and we need to make sure that the image is what it seems to be or it carries something hidden which is not good for our system. and for solving this problem here. Enters the cryptographic security guards which ensures that the image is secure and authentic. which is called the Docker Content Trust (DCT) keys. The vital component of Docker’s security framework, Docker Content Trust (DCT) Keys guarantee the integrity and validity of container images in a Docker context. therefore it is essential to maintaining the security of the Docker image lifecycle. A safe and verifiable trust paradigm for Docker container images is established in large part thanks to Docker Content Trust Keys.

Types of DCT keys

Private Key

The owner or entity that signs Docker images is the one that keeps the private key safe. and it is recommend to keep it safe and private. It is still private and can be used to create distinct cryptographic signatures and sign pictures. private key is used for image signing and the image verification.

Public Key

The public key is the source of the public. for Docker clients to validate the signatures that are associated to it and the public key is shared and made available for users. It is a method used to verify the integrity and authenticity of signed Docker images.

It is an additional cryptographic key meant for public which is used for distribution and accessibility. and it is Safely stored inside a Docker Notary Server, which serving as a reliable source for trust artifacts. is utilized by customers to verify and decrypt picture signatures made using the matching private key.

To know about the difference between Public and Private Key, please refer this Article: Private vs Public Key

How to Generate Docker Content Trust Keys?

Firstly start with installation of Docker to your local system and Creating a key is an important task. Each Docker repository requires a different key pair to be created as part of the process of creating Docker Content Trust Keys. To make a distinct key pair for every Docker repository, a set of exact procedures must be followed in the DCT key generation process. The steps are as follows:

Initiating Key Generation

you can give any unique name to your key. and this is the syntax for generating the key.

docker trust key generate <repository-name>

in the place of <repository-name> replace with the name of the Docker repository.

Generating Private and Public Keys

A public key and private key are created using these command which is mentioned below. While the public key is added to the repository for image verification, the private key is kept safe.

following the creation of the keys using the command

docker trust key list --dir .

You can Use the docker trust key list command which list the produced keys details and make sure to specify the`–dir . ` option to point to the keys’ storage directory. This gives details about the generated key pair, such as key IDs and cryptographic information. which helps you understand the process in more easy way.

Roles of Docker Content Trust (DCT) Keys:

Image Signing process

when you docker image is signed with the keys then the private key which is connected with your repository is utilized and further create a cryptographic code for that image. This code signature work as an unique identifier which concern that the image comes from the authentic source and it is trustworthy.

Image Verification

DCT client uses the public key which is connected with the docker repository which is used for verifying the key is match with unique signature of the DCT image when we are pulling or working on the Docker image. This verification process make sure that the image has not been having malicious activities. and follows the security rules.

Trust on First Use (TOFU)

DCT is working on the model called “Trust on first use” the public key is obtained and cached the first time an image from a particular repository is encountered. furthermore this cached key is applied to more verifications. by using this technique DCT knows the image is in use or not and easily keep tracks on the suspicious activities which gradually enhancing the reliability of the Docker images

Additional Tips for Managing Docker Content Trust Keys

  • Secure Storage: Store private keys securely and make sure you store it somewhere as a backup because there is no other way for signing the image. ensuring access is limited to authorized personnel which enhance security.
  • Regular Key Rotation: Periodically rotate Docker Content Trust Keys to enhance security and mitigate potential risks associated with prolonged key usage .
  • Key Backup: Implement a robust key backup strategy to prevent data loss. and the best way you can note down it offline where it is safe and you access it easily.
  • Secure Key Distribution: Use secure channels to distribute public keys in order to guard against manipulation. Public keys are critical for Docker clients to verify image authenticity.

How to use Docker Content Trust(DCT)?

Step 1: Enabling DCT

Firstly you need to set up an environment variable at the top. which enables the DCT and then you can enable it by setting it’s value 1 as mentioned below.

The DOCKER_CONTENT_TRUST = 1 is used for setting up DCT . for enabling setting its value = 1 as mentioned below you can also disable it by setting up its value = 0.

export "DOCKER_CONTENT_TRUST=1

and make if you are trying to pull the image. so the image is not present in your system locally. otherwise it gives an error message.

Enabling DCT environment

Step 2: Creation and set up of DCT keys

The authentication process works on the basis of unique keys so in the second step firstly you need to generate it. Signing keys are the important part of the DCT firstly you need to generate and then if you want to you can attach it with some tags follows the process as mentioned below.

The following command is used for creating key:

 "docker trust key generate <Your_key> "  to create signing key pairs.

generating key

Step 3: Sign your Docker Image

Signing is an important process for Docker images and you need to be concern about its authenticity before you pushing them to a registry. And by you need add your key as a signer by following command mentioned below:

docker trust signer add --key <"Key">/ <repository>

add-a-signer

A key pair is required in order to sign a Docker image. The images are signed to prove the authenticity and verify the Docker images.We can now sign our docker image by running this command.

if everything goes well then the a message of success comes on the console as showed in the image below

docker trust sign <name-of-image

sign docker image

Step 4: Push your images to Registry

now in this step you push your image to a Docker registry using docker hub after that you signed. Make sure the images you signed is pushed to the respective registry. furthermore if you want so you can sign a specific tag and push it up to the registry the key generated by you.

Alternatively, this command can be used to push an image after the keys have been imported.

docker image push <registry>/<image>

pushing the image

Step 5: Verify Signed Images

if you want to know that the DCT is working well so. we can verify the signed Docker Images. Verifying signed images is important for confirming the authenticity and trustworthiness of Docker images. if you verify the signed image so it lower the chances of unwanted outcomes.

We can use this command to confirm the our images is properly signed.

docker trust inspect --pretty <image-name>

by using this command you can also check the details like signer keys, details about ID’s and status about the specified image. It also display details about the entity who signed the image, so you can take surety about its origin.

it also shows Signing Status which Indicates whether the image has been successfully signed or not and if the image is properly signed so you can view it in console in readable format.

Additional Tips

  • Self-Hosted Registries: you can also Set up your Notary server for signature management.
  • other tools: if you want so you can also explores Cosign for better signing experience.
  • Automation: you can add with DCT with CI/CD pipelines for automation and better process.

Conclusion

DCT is an effective method for verifying the authenticity of Docker images is provided by Docker. This security feature make containerization process more secure and reliable. and clients doesn’t need to worry about image security and as we now that the maintaining security best practices. because “prevention is better than cure” just like it if you want to provide more security to your image you must need to enable DCT in your Docker image. Docker images, Docker Content Trust is an essential tool for safeguarding containerized applications and significantly improves security.

Docker Content Trust – FAQs

Why Is Docker Content Trust Is Important?

Docker Content Trust ensures that only verified and unaltered images are used,
and it enhancing the security of containerized applications against
 unethical activities. and provide a robust security.

What are the benefits of using DCT?

DCT enhance the security against malicious activities and secure the image. 
so you can deploy your images securely with confidence. and it provide the security 
to your whole container ecosystem. and Protects against compromised or malicious images.

Can Docker Content Trust Be Disabled After Enabling It?

Yes, you can  disable Docker Content Trust but it's
good practice to keep it enabled to maintain image security.

How do I generate DCT keys?

you can generate DCT keys  docker trust key generate "key-name"

Can Docker Content Trust work with private Docker registries?

Yes, Docker Content Trust can work with private registries.



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