fedmsg (Fedora Messaging) Certs, Keys, and CA - SOP

fedmsg sends JSON-encoded messages from many services to a zeromq messaging bus. We’re not concerned with encrypting the messages, only with signing them so an attacker cannot spoof.

Every instance of each service on each host has its own cert and private key, signed by the CA. By convention, we name the certs <service>-<fqdn>.\{crt,key} For instance, bodhi has the following certs:

Scripts to generate new keys, sign them, and revoke them live in the ansible repo in ansible/roles/fedmsg/files/cert-tools/. The keys and certs themselves (including ca.crt and the CRL) live in the private repo in private/fedmsg-certs/keys/

fedmsg is locally configured to find the key it needs by looking in /etc/fedmsg.d/ssl.py which is kept in ansible in ansible/roles/fedmsg/templates/fedmsg.d/ssl.py.erb.

Each service-host has its own key. This means:

The attempt here is to minimize the number of potential attack vectors. Each private key should be readable only by the service that needs it. bodhi runs under mod_wsgi in apache and should run as its own unique bodhi user (not as apache). The permissions for its.phx2.fedoraproject.org private_key, when deployed by ansible, should be read-only for that local bodhi user.

For more information on how fedmsg uses these certs see http://fedmsg.readthedocs.org/en/latest/crypto.html

Usage of the main scripts is described in more detail below. They are located in ansible/rolesfedmsg/files/cert-tools.

Before you use them, you’ll need to point them at the right directory to modify. By default, this is ~/private/fedmsg-certs/keys/. You can change that by editing ansible/roles/fedmsg/files/cert-tools/vars in the event that you have the private repo checked out to an alternate location.

There are other configuration values defined in that script. Most will not need to be changed.

There is a script in ansible/roles/fedmsg/files/cert-tools/ named rebuild-all-fedmsg-certs. You can run it with no arguments to wipe out the old and generate a new CA root certificate, a signing cert and key, and all key/cert pairs for all service-hosts.

First, checkout the ansible private repo as that’s where the keys are going to be stored. The scripts will assume this is checked out to ~/private.

In ansible/roles/fedmsg/files/cert-tools run:

For instance, if we bring up a new app host, app10.phx2.fedoraproject.org, we’ll need to generate a new cert/key pair for each fedmsg-enabled service that will be running on it, so you’d run:

Just creating the keys isn’t quite enough, there are four more things you’ll need to do.

The private keys are created in your checkout of the private repo under ~/private/private/fedmsg-certs/keys . There will be four files for each cert you created: <hexdigits>.pem (ex: 5B.pem) and <service>-<fqdn>.\{crt,csr,key} git add, commit, and push all of those.

Second, You need to edit ansible/roles/fedmsg/files/cert-tools/rebuild-all-fedmsg-certs and add the argument of the commands you just ran, so that next time certs need to be blown away and recreated, the new service-hosts will be included. For the examples above, you would need to add to the list:

You need to ensure that the keys are distributed to the host with the proper permissions. Only the bodhi user should be able to access bodhi’s private key. This can be accomplished by using the fedmsg::certificate in ansible. It should distribute your new keys to the correct hosts and correctly permission them.

Lastly, if you haven’t already updated the global fedmsg config, you’ll need to. You need to add your new service-node to fedmsg.d/endpoint.py and to fedmsg.d/ssl.py. Those can be found in ansible/roles/fedmsg/templates/fedmsg.d. See http://fedmsg.readthedocs.org/en/latest/config.html for more information on the layout and meaning of those files.

In ansible/roles/fedmsg/files/cert-tools run:

This will alter private/fedmsg-certs/keys/crl.pem which should be picked up and served publicly, and then consumed by all fedmsg consumers globally.

crl.pem is publicly available at http://fedoraproject.org/fedmsg/crl.pem