Verifying container image signatures

Digital signatures provide a way for consumers of content to ensure that what they download is both authentic (it originated from the expected source) and has integrity (it is what we expect it to be). All images for the Event Streams certified container in the IBM Entitled Registry are signed following the approach from Red Hat.

You can use the signature to verify that the images came from IBM when they are pulled onto the system.

Before you begin

Ensure that the following command-line tools are installed on your computer. On Linux systems, these images can typically be installed by using the package manager.

On the computer where the command-line tools are installed, copy the following version-specific text block exactly as shown into a text editor, and save it in a file named acecc-public.gpg. The following text block represents the Event Streams-certified container public key in the GNU Privacy Guard format.

Obtaining the container images

Obtain the list of Event Streams-certified container images to verify as described in the following sections.

Prepare your bastion host

Ensure you meet the following prerequisites before downloading the CASE archive and obtaining the images:

A computer with internet access on which you can run the required commands. This computer must also have access to the cluster, and is referred to as a bastion host.
A cluster that is already set up and running a supported version of the Red Hat OpenShift Container Platform. For more information, see the support matrix for supported versions.
A private Docker registry that can be accessed by the cluster and the bastion host, and which will be used to store all images on your restricted network.

If the cluster has a bastion host which has access to the public internet, then the following steps can be performed from the bastion host.

Note: In the absence of a bastion host, prepare a portable device that has access to the public internet to download the CASE archive and images, and also has access to the target registry where the images will be mirrored.

Download the CASE archive

Download the Container Application Software for Enterprises (CASE) archive. This archive, which is typically provided for installing within a restricted network, includes metadata and files that you will require later.

Complete the following steps to download the CASE archive:

Configure the internal repository for downloading the CASE archive:

oc ibm-pak config repo 'default' -r "https://github.com/IBM/cloud-pak/raw/master/repo/case/" --enable

Run the following command to download, validate, and extract the CASE archive.

oc ibm-pak get ibm-eventstreams

Where <path-to-case-archive> is the location of the CASE archive. If you are running the command from the current location, set the path to the current directory (.). The following output is displayed:

Downloading and extracting the CASE ...
- Success
Retrieving CASE version ...
- Success
Validating the CASE ...
Validating the signature for the ibm-eventstreams CASE...
- Success
Creating inventory ...
- Success
Finding inventory items
- Success
Resolving inventory items ...
Parsing inventory items
- Success
Download of CASE: ibm-eventstreams, version: 3.3.2 is complete

Verify that the CASE archive and images .csv files have been generated for the Event Streams. For example, ensure you have the following files generated for the Event Streams CASE.

$ tree ~/.ibm-pak

├── config
│   └── config.yaml
├── data
│   ├── cases
│   │   └── ibm-eventstreams
│   │       └── 3.3.2
│   │           ├── caseDependencyMapping.csv
│   │           ├── charts
│   │           ├── ibm-eventstreams-3.3.2-airgap-metadata.yaml
│   │           ├── ibm-eventstreams-3.3.2-charts.csv
│   │           ├── ibm-eventstreams-3.3.2-images.csv
│   │           ├── ibm-eventstreams-3.3.2.tgz
│   │           └── resourceIndexes
│   │               └── ibm-eventstreams-resourcesIndex.yaml
│   └── mirror
└── logs
    └── oc-ibm_pak.log

9 directories, 8 files

Obtain the files

After meeting the required prerequisites and downloading the CASE archive, obtain the following files:
- The downloaded CASE archives, which contain metadata for the container images required to deploy each Event Streams capability. Each CASE archive also contains the required scripts to mirror images to a private registry, and to configure the target cluster to use the private registry as a mirror.
- Generated comma-separated value (CSV) files listing the images. Obtain an IBM Entitled Registry entitlement key from the IBM Container software library. The CSV files, combined with your entitlement key, are used for downloading or mirroring the images manually.
To verify the image signatures for a Event Streams-certified container, use the file that is named in the format ibm-eventstreams-<v.r.m>-images.csv, where v.r.m represents the Event Streams CASE version.

Use a shell script to parse through the CSV file and print out the list of “manifest list images” with their digests or tags. You can use the listed names when pulling and verifying image signatures. In the tail command, /tmp/cases represents the directory where you downloaded the CASE archive.

List images by digest:

tail -q -n +2 /tmp/cases/ibm-eventstreams-*-images.csv | while IFS="," read registry image_name tag digest mtype os arch variant insecure digest_source image_type groups; do
if [[ "$mtype" == "LIST" ]]; then
    echo "$registry/$image_name@$digest"
fi
done

List images by tag:

tail -q -n +2 /tmp/cases/ibm-eventstreams-*-images.csv | while IFS="," read registry image_name tag digest mtype os arch variant insecure digest_source image_type groups; do
if [[ "$mtype" == "LIST" ]]; then
    echo "$registry/$image_name:$tag"
fi
done

Note: You can also copy the output to a file for ease of reference while verifying the image signatures.

Verifying the signature

To verify the image signatures, complete the following steps:

Import the Event Streams-certified container public key on the computer where you saved the public key to a file as described in the Before you begin section.
```
sudo gpg --import acecc-public.gpg
```
Note: This step needs to be done only once on each computer that you use for signature verification.
Calculate the fingerprint.
```
fingerprint=$(sudo gpg --fingerprint --with-colons | grep fpr | tr -d 'fpr:')
```
This command stores the key’s fingerprint in an environment variable called fingerprint, which is needed for the command to verify the signature.

Note: When you exit your shell session, the variable will be deleted. The next time you log in to your computer, you can set the environment variable again by rerunning the command in this step.
Log in to skopeo to access the entitled registry. Use cp as the username and your entitlement key as the password. For example:
```
skopeo login cp.icr.io --username cp --password myEntitlementKey
```
Create a directory (for example, images) for the image. Then use skopeo to pull the image into local storage, where imageName represents the image name.
```
mkdir images
skopeo copy docker://<imageName> dir:./images
```
For example:
```
mkdir images
skopeo copy docker://icr.io/cpopen/ibm-eventstreams-catalog:3.0.0-00000000-000000 dir:./images
```
This command downloads the image as a set of files and places them in the images directory, or in a directory that you specified. A manifest file named images/manifest.json, and a set of signature files named images/signature-1, images/signature-2, and images/signature-3 are added to the directory. You will use these files to verify the signature in the next step.

Verify the signature for each required image, where imageName is the name of the image and signature-N relates to a format for the name.

sudo skopeo standalone-verify ./images/manifest.json <imageName> ${fingerprint} ./images/<signature-N>

For example:

sudo skopeo standalone-verify ./images/manifest.json icr.io/cpopen/ibm-eventstreams-catalog:3.0.0-00000000-000000 ${fingerprint} ./images/signature-1

You will receive a confirmation similar to the following:

Signature verified, digest sha256:0000000000000000000000000000000000000000000000000000000000000000