Why this document?

The Debian Derivatives Guidelines (Derivatives/Guidelines) encourages "derivative distributions to mention and define their relationship with Debian". Because this seems like a great idea to us, we wrote this statement that not only covers Tails' relationship with Debian, but also Tails' relationship with any one of its upstream projects.

Summary

For various reasons Tails tries to diverge by the smallest possible amount from its upstream projects, and especially from Debian:

• We want to share our work with the rest of the Free Software community.

• We value maintainability very much: we believe our users are best served if we keep the amount of work needed to maintain Tails the smallest possible.

How

Upstream software

We try to push our changes upstream when we need to modify software we ship. This often requires us to write code in a generic way, rather than implementing ad-hoc hacks to fit our specific needs: e.g. we often need to make the stuff we need opt-in and add configuration options.

Debian packaging

Debian offers great amounts of flexibility to derivative developers, so we seldom need to modify Debian-specific parts of the software we ship. In the rare cases we need to:

• we at least inform the relevant Debian maintainers, so that they have a chance to enhance their packages to fit our needs;

• in many cases, we write and propose patches that would allow us to install unmodified Debian packages in Tails.

We also encourage potential contributors to improve Tails by working on Debian.

Debian Bug tracking system

We file and contribute to RFP and WNPP bugs so that software we need lands in Debian. More generally, we heavily use the Debian infrastructure such as the BTS.

We use usertags (documentation, reporting) to track bugs we are interested in on the Debian BTS.

See the full and up-to-date list of bugs:

• sorted by usertag;

• sorted by severity.

Warning: do not use tags that are already defined globally on the BTS.

GNOME

See the issues that affect Tails in the GNOME bug tracker.

Exceptions

A number of Tails features are not available in Debian. For example:

• In order to prevent cold boot attacks and various memory forensics, Tails erases most memory on shutdown.

• Tails changes the MAC address of network interfaces to random values.

Most of the time, we did not contribute these features upstream due to the combination of these factors:

• The feature is meant to provide certain security guarantees. Users should be able to rely on this feature to make security decisions.

• The feature requires deep integration into several layers of the operating system. For example, Tails' MAC address spoofing feature plugs into udev, NetworkManager, GDM, and more.

  The set of Tails systems is very homogeneous, while Debian systems are highly diverse: multiple init systems, desktop environments, network interface management software, firewall configuration tools, etc.

  In the context of Tails, most of these parameters are constants we can rely upon. Our automated tests can verify that the feature works in Tails.

  While in the context of Debian, these parameters are variables, which leads to combinatorial explosion. So, sometimes, ensuring a security feature works reliably in all possible Debian setups, is simply impossible: there are simply too many cases to consider, reason about, and do quality assurance for.

  Additionally, even if we could ensure that a given feature provides the expected security benefits today in all such combinations, any package update tomorrow could break it.