Set up a debusine signing worker

Introduction

debusine-signing is a signing service for Debusine, holding private keys and using them to sign data on behalf of Debusine. It is a daemon that connects (via HTTP API and WebSockets) to a Debusine server, waits for tasks and executes tasks locally.

Notes for production deployments

debusine-signing manages sensitive data: an attacker with the ability to extract private keys in the clear would be able to construct intermediary attacks that could go undetected for long periods of time. None of debusine-signing’s interfaces allow extracting private keys, but deployments that involve high-value keys should take some extra care.

  • The signing worker uses its own database, which should not be accessible by the Debusine server. In a small deployment it can be local to the signing worker, but if it is on a separate system then that should be distinct from the system hosting the Debusine server’s database.

  • Limit direct user access as much as possible.

  • Apply strict firewall rules. debusine-signing does not require any inbound connections.

  • You may need to back up /etc/debusine/signing/*.key; these keys allow decrypting private keys stored in the signing database, so avoid storing backups of the signing database and these keys in the same place.

  • The signing database includes audit logs. In the event of an attack that is not suspected of having been able to extract private key material directly, these audit logs may be useful in determining which keys need to be rotated.

Initial setup

Install the debusine-signing package. The Initial setup using debusine server has the instructions how to add the debusine repository.

$ sudo apt install postgresql  # if you need to install PostgreSQL
$ sudo apt install debusine-signing

To know what the package does during installation see the What the package does on installation section. Follow the steps below to finalize the set-up.

  1. By default, the package is configured to use a PostgreSQL database using the default local Unix socket and the authentication is done at the user level. The package creates a “debusine-signing” Unix account.

    The database configuration can be edited in /etc/debusine/signing/db_postgresql.py .

  2. Create the file /etc/debusine/signing/config.ini . Use /usr/share/doc/debusine-signing/examples/config.ini as an example:

    $ sudo cp /usr/share/doc/debusine-signing/examples/config.ini /etc/debusine/signing/
$ sudo editor /etc/debusine/signing/config.ini

    Change the api-url in the configuration file as needed. Note that it must be HTTPS: see Configure Nginx with an HTTPS certificate for how to set this up, especially if you are using a local self-signed certificate.

  3. Generate a private key to be used to encrypt other private keys:

    $ sudo -u debusine-signing debusine-signing generate_service_key /etc/debusine/signing/0.key

  4. Restart debusine-signing with the new configuration and group:

    $ sudo systemctl restart debusine-signing

    The logs can be seen in /var/log/debusine/signing/.

  5. Following the restart, the token will appear in /etc/debusine/signing/token and in the log file /var/log/debusine/signing/signing.log. The debusine admin should approve the tokens pending for approval. Nothing needs to be done from the side of debusine-signing.

Managing debusine-signing

Use the systemctl command to start (done automatically by the package), stop or restart debusine-signing:

$ sudo systemctl start debusine-signing
$ sudo systemctl stop debusine-signing
$ sudo systemctl status debusine-signing

The default configuration logs relevant information in /var/log/debusine/signing/signing.log. The log file and log level can be changed in /etc/debusine/signing/config.ini.

If debusine-signing outputs the log to the stdout/stderr the logs are available via:

$ journalctl --unit debusine-signing

Troubleshooting

Information about the state of debusine-signing can be found via:

  1. systemctl status debusine-signing to verify that the service is running

  2. /var/log/debusine/signing/signing.log to see any error messages

  3. journalctl -u debusine-signing for other information

To change the settings of debusine-signing, for example to increase the logging level:

$ sudo editor /etc/debusine/signing/config.ini # change log-level
$ sudo systemctl restart debusine-signing

debusine-signing can be launched without systemd which might be useful for troubleshooting. Run it with the same debusine-signing user. For example:

$ sudo systemctl stop debusine-signing

# for example, comment out log-file so the log is to stderr
$ sudo editor /etc/debusine/signing/config.ini

# execute it with the correct user
$ sudo -u debusine-signing debusine-signing signing_worker

debusine-signing can also be launched using a different user for debugging purposes. The configuration (config.ini and token files) in the directory $HOME/.config/debusine/signing have higher priority than the global configuration, /etc/debusine/signing .

What the package does on installation

  • Creates the debusine-signing user

  • Installs a systemd service (named debusine-signing)

  • Creates the directories /etc/debusine/signing, /var/log/debusine/signing, and /var/lib/debusine-signing