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.
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.
|trustsandbox||A container with the latest version of Docker Engine and with some preconfigured certificates. This is your sandbox where you can use the
|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 these components. They are built into the Docker Hub for you. For the sandbox, however, you build your own entire, mock production environment.
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
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
trustsandbox container, the Notary server, and the Registry server.
Create a new
trustsandboxdirectory and change into it.
$ mkdir trustsandbox $ cd trustsandbox
Create a file called
docker-compose.ymlwith your favorite editor. For example, using vim:
$ touch docker-compose.yml $ vim docker-compose.yml
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
Save and close the file.
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
$ docker container exec -it trustsandbox sh / #
Test some trust operations
Now, pull some images from within the
dockerimage 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
Tag it to be pushed to our sandbox registry:
/ # docker tag docker/trusttest sandboxregistry:5000/test/trusttest:latest
Enable content trust.
/ # export DOCKER_CONTENT_TRUST=1
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.
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
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.
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.
trustsandboxshell and container running.
Open a new interactive terminal from your host, and obtain a shell into the
$ docker container exec -it sandboxregistry bash root@65084fc6f047:/#
List the layers for the
test/trusttestimage 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
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
Add malicious data to one of the
root@65084fc6f047:/# echo "Malicious data" > data
Go back to your
/ # 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
trusttest:latestimage 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.
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 firstname.lastname@example.org.
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