Play in a content trust sandbox

Estimated reading time: 8 minutes

This page explains how to set up and use a sandbox for experimenting with trust. The sandbox allows you to configure and try trust operations locally without impacting your production images.

Before working through this sandbox, you should have read through the trust overview.

Prerequisites

These instructions assume you are running in Linux or macOS. You can run this sandbox on a local machine or on a virtual machine. You need to have privileges to run docker commands on your local machine or in the VM.

This sandbox requires you to install two Docker tools: Docker Engine >= 1.10.0 and Docker Compose >= 1.6.0. To install the Docker Engine, choose from the list of supported platforms. To install Docker Compose, see the detailed instructions here.

What is in the sandbox?

If you are just using trust out-of-the-box you only need your Docker Engine client and access to the Docker Hub. The sandbox mimics a production trust environment, and sets up these additional components.

Container Description
trustsandbox A container with the latest version of Docker Engine and with some preconfigured certificates. This is your sandbox where you can use the docker client to test trust operations.
Registry server A local registry service.
Notary server The service that does all the heavy-lifting of managing trust

This means you run your own content trust (Notary) server and registry. If you work exclusively with the Docker Hub, you would not need with these components. They are built into the Docker Hub for you. For the sandbox, however, you build your own entire, mock production environment.

Within the trustsandbox container, you interact with your local registry rather than the Docker Hub. This means your everyday image repositories are not used. They are protected while you play.

When you play in the sandbox, you also create root and repository keys. The sandbox is configured to store all the keys and files inside the trustsandbox container. Since the keys you create in the sandbox are for play only, destroying the container destroys them as well.

By using a docker-in-docker image for the trustsandbox container, you also don’t pollute your real Docker daemon cache with any images you push and pull. The images are stored in an anonymous volume attached to this container, and can be destroyed after you destroy the container.

Build the sandbox

In this section, you use Docker Compose to specify how to set up and link together the trustsandbox container, the Notary server, and the Registry server.

  1. Create a new trustsandbox directory and change into it.

     $ mkdir trustsandbox
 $ cd trustsandbox

  2. Create a file called docker-compose.yml with your favorite editor. For example, using vim:

     $ touch docker-compose.yml
 $ vim docker-compose.yml

  3. Add the following to the new file.

     version: "2"
 services:
   notaryserver:
     image: dockersecurity/notary_autobuilds:server-v0.5.1
     volumes:
       - notarycerts:/var/lib/notary/fixtures
     networks:
       - sandbox
     environment:
       - NOTARY_SERVER_STORAGE_TYPE=memory
       - NOTARY_SERVER_TRUST_SERVICE_TYPE=local
   sandboxregistry:
     image: registry:2.4.1
     networks:
       - sandbox
     container_name: sandboxregistry
   trustsandbox:
     image: docker:dind
     networks:
       - sandbox
     volumes:
       - notarycerts:/notarycerts
     privileged: true
     container_name: trustsandbox
     entrypoint: ""
     command: |-
         sh -c '
             cp /notarycerts/root-ca.crt /usr/local/share/ca-certificates/root-ca.crt &&
             update-ca-certificates &&
             dockerd-entrypoint.sh --insecure-registry sandboxregistry:5000'
 volumes:
   notarycerts:
     external: false
 networks:
   sandbox:
     external: false

  4. Save and close the file.

  5. Run the containers on your local system.

     $ docker-compose up -d

    The first time you run this, the docker-in-docker, Notary server, and registry images are downloaded from Docker Hub.

Play in the sandbox

Now that everything is setup, you can go into your trustsandbox container and start testing Docker content trust. From your host machine, obtain a shell in the trustsandbox container.

$ docker container exec -it trustsandbox sh
/ #

Test some trust operations

Now, pull some images from within the trustsandbox container.

  1. Download a docker image to test with.

     / # docker pull docker/trusttest
 docker pull docker/trusttest
 Using default tag: latest
 latest: Pulling from docker/trusttest

 b3dbab3810fc: Pull complete
 a9539b34a6ab: Pull complete
 Digest: sha256:d149ab53f8718e987c3a3024bb8aa0e2caadf6c0328f1d9d850b2a2a67f2819a
 Status: Downloaded newer image for docker/trusttest:latest

  2. Tag it to be pushed to our sandbox registry:

     / # docker tag docker/trusttest sandboxregistry:5000/test/trusttest:latest

  3. Enable content trust.

     / # export DOCKER_CONTENT_TRUST=1

  4. Identify the trust server.

     / # export DOCKER_CONTENT_TRUST_SERVER=https://notaryserver:4443

    This step is only necessary because the sandbox is using its own server. Normally, if you are using the Docker Public Hub this step isn’t necessary.

  5. Pull the test image.

     / # docker pull sandboxregistry:5000/test/trusttest
 Using default tag: latest
 Error: remote trust data does not exist for sandboxregistry:5000/test/trusttest: notaryserver:4443 does not have trust data for sandboxregistry:5000/test/trusttest

    You see an error, because this content doesn’t exist on the notaryserver yet.

  6. Push and sign the trusted image.

     / # docker push sandboxregistry:5000/test/trusttest:latest
 The push refers to a repository [sandboxregistry:5000/test/trusttest]
 5f70bf18a086: Pushed
 c22f7bc058a9: Pushed
 latest: digest: sha256:ebf59c538accdf160ef435f1a19938ab8c0d6bd96aef8d4ddd1b379edf15a926 size: 734
 Signing and pushing trust metadata
 You are about to create a new root signing key passphrase. This passphrase
 will be used to protect the most sensitive key in your signing system. Please
 choose a long, complex passphrase and be careful to keep the password and the
 key file itself secure and backed up. It is highly recommended that you use a
 password manager to generate the passphrase and keep it safe. There will be no
 way to recover this key. You can find the key in your config directory.
 Enter passphrase for new root key with ID 27ec255:
 Repeat passphrase for new root key with ID 27ec255:
 Enter passphrase for new repository key with ID 58233f9 (sandboxregistry:5000/test/trusttest):
 Repeat passphrase for new repository key with ID 58233f9 (sandboxregistry:5000/test/trusttest):
 Finished initializing "sandboxregistry:5000/test/trusttest"
 Successfully signed "sandboxregistry:5000/test/trusttest":latest

    Because you are pushing this repository for the first time, Docker creates new root and repository keys and asks you for passphrases with which to encrypt them. If you push again after this, it only asks you for repository passphrase so it can decrypt the key and sign again.

  7. Try pulling the image you just pushed:

     / # docker pull sandboxregistry:5000/test/trusttest
 Using default tag: latest
 Pull (1 of 1): sandboxregistry:5000/test/trusttest:latest@sha256:ebf59c538accdf160ef435f1a19938ab8c0d6bd96aef8d4ddd1b379edf15a926
 sha256:ebf59c538accdf160ef435f1a19938ab8c0d6bd96aef8d4ddd1b379edf15a926: Pulling from test/trusttest
 Digest: sha256:ebf59c538accdf160ef435f1a19938ab8c0d6bd96aef8d4ddd1b379edf15a926
 Status: Downloaded newer image for sandboxregistry:5000/test/trusttest@sha256:ebf59c538accdf160ef435f1a19938ab8c0d6bd96aef8d4ddd1b379edf15a926
 Tagging sandboxregistry:5000/test/trusttest@sha256:ebf59c538accdf160ef435f1a19938ab8c0d6bd96aef8d4ddd1b379edf15a926 as sandboxregistry:5000/test/trusttest:latest

Test with malicious images

What happens when data is corrupted and you try to pull it when trust is enabled? In this section, you go into the sandboxregistry and tamper with some data. Then, you try and pull it.

  1. Leave the trustsandbox shell and container running.

  2. Open a new interactive terminal from your host, and obtain a shell into the sandboxregistry container.

    $ docker container exec -it sandboxregistry bash
root@65084fc6f047:/#

  3. List the layers for the test/trusttest image you pushed:

    root@65084fc6f047:/# ls -l /var/lib/registry/docker/registry/v2/repositories/test/trusttest/_layers/sha256
total 12
drwxr-xr-x 2 root root 4096 Jun 10 17:26 a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
drwxr-xr-x 2 root root 4096 Jun 10 17:26 aac0c133338db2b18ff054943cee3267fe50c75cdee969aed88b1992539ed042
drwxr-xr-x 2 root root 4096 Jun 10 17:26 cc7629d1331a7362b5e5126beb5bf15ca0bf67eb41eab994c719a45de53255cd

  4. Change into the registry storage for one of those layers (this is in a different directory):

    root@65084fc6f047:/# cd /var/lib/registry/docker/registry/v2/blobs/sha256/aa/aac0c133338db2b18ff054943cee3267fe50c75cdee969aed88b1992539ed042

  5. Add malicious data to one of the trusttest layers:

    root@65084fc6f047:/# echo "Malicious data" > data

  6. Go back to your trustsandbox terminal.

  7. List the trusttest image.

    / # docker image ls | grep trusttest
REPOSITORY                            TAG                 IMAGE ID            CREATED             SIZE
docker/trusttest                      latest              cc7629d1331a        11 months ago       5.025 MB
sandboxregistry:5000/test/trusttest   latest              cc7629d1331a        11 months ago       5.025 MB
sandboxregistry:5000/test/trusttest   <none>              cc7629d1331a        11 months ago       5.025 MB

  8. Remove the trusttest:latest image from our local cache.

    / # docker image rm -f cc7629d1331a
Untagged: docker/trusttest:latest
Untagged: sandboxregistry:5000/test/trusttest:latest
Untagged: sandboxregistry:5000/test/trusttest@sha256:ebf59c538accdf160ef435f1a19938ab8c0d6bd96aef8d4ddd1b379edf15a926
Deleted: sha256:cc7629d1331a7362b5e5126beb5bf15ca0bf67eb41eab994c719a45de53255cd
Deleted: sha256:2a1f6535dc6816ffadcdbe20590045e6cbf048d63fd4cc753a684c9bc01abeea
Deleted: sha256:c22f7bc058a9a8ffeb32989b5d3338787e73855bf224af7aa162823da015d44c

    Docker does not re-download images that it already has cached, but we want Docker to attempt to download the tampered image from the registry and reject it because it is invalid.

  9. Pull the image again. This downloads the image from the registry, because we don’t have it cached.

    / # docker pull sandboxregistry:5000/test/trusttest
Using default tag: latest
Pull (1 of 1): sandboxregistry:5000/test/trusttest:latest@sha256:35d5bc26fd358da8320c137784fe590d8fcf9417263ef261653e8e1c7f15672e
sha256:35d5bc26fd358da8320c137784fe590d8fcf9417263ef261653e8e1c7f15672e: Pulling from test/trusttest

aac0c133338d: Retrying in 5 seconds
a3ed95caeb02: Download complete
error pulling image configuration: unexpected EOF

    The pull did not complete because the trust system couldn’t verify the image.

More play in the sandbox

Now, you have a full Docker content trust sandbox on your local system, feel free to play with it and see how it behaves. If you find any security issues with Docker, feel free to send us an email at security@docker.com.

Clean up your sandbox

When you are done, and want to clean up all the services you’ve started and any anonymous volumes that have been created, just run the following command in the directory where you’ve created your Docker Compose file:

    $ docker-compose down -v
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