[[!meta date="Wed, 15 Nov 2017 10:00:00 +0000"]]
[[!meta title="Have your cake and eat it, too!"]]
Reproducible Tails builds
We have received the Mozilla Open Source Support award in order to make Tails
ISO images build reproducibly. This project was on our roadmap for 2017 and
with the release of Tails 3.3 we are proud to present one of the world's first
reproducible ISO images of a Linux operating system.
From source code to binary code
When we write software, we do this using programming languages which a
human can read and understand. This is called the _source code_. One can
imagine source code much like a very precise recipe. Such a recipe
describes an exact procedure: which ingredients and which amount of
ingredients do you need? How should they be mixed together at which
temperature should they be cooked or baked? The recipe will even
describe the expected outcome: how the meal should look and taste like.
When we generate a Tails ISO image, our source code and the Debian
packages we include are assembled into a binary ISO image,
much like when the ingredients of the recipe are mixed together,
one obtains the meal. The amounts and ingredients of this meal cannot be
easily reverse engineered. The result of *our* cooking process is a Tails ISO
image which users download and install onto a USB stick.
We, chefs and aides in the kitchen (Tails developers and contributors),
provide you, our users, with several means to verify that this ISO image
is indeed the one we want you to download, either using our
Firefox add-on which does this verification
automatically for you or by using our OpenPGP signature. Both of these
verification methods simply tell you that the ISO image is the image
which we want you to download: That the meal you get is indeed the meal
that you've ordered, and not a meal which has been poisoned or exchanged
by an evil waiter (such as a download mirror).
However, even with such sophisticated verification methods, it is still
impossible to trace back the meal to the recipe: Does the meal contain
only the ingredients it is supposed to contain? Or could unauthorized
personnel have broken into the kitchen at night, and then poisoned the
ingredients and made the oven cook at 50 degrees higher than displayed?
In other words, could a malicious entity have compromised our build
machines? That's what reproducible builds help verify and protect
What's a reproducible build?
> Reproducible builds are a set of software development practices that create
> a verifiable path from human readable source code to the binary code used
> by computers. *(quoted from https://reproducible-builds.org/)*
In other words, with reproducible builds, each cooking process of the same
recipe is exactly repeatable.
At Tails, we have worked during a year to implement such a set of
practices. This makes it now possible to compare ISO images built by
multiple parties from the same source code and Debian packages,
and to ensure that they all result in exactly the same ISO image.
Or again, using our cooking metaphor: Several of us will cook the meal, compare
that we all cooked the same meal and only once we're sure about that, we will
deliver it to you.
We all can thus gain confidence that no broken oven has introduced
malicious code or failures: or we would notice it before delivering the
What does this mean for you as a user?
This does not change anything in the way you download and install Tails,
and you don't have to make additional verifications. It simply helps
trust that the Tails ISO image that we distribute is indeed coming from
the source code and Debian packages it is meant to be made of. With reproducible Tails, it
only takes one knowledgeable person to build Tails and compare with the
ISO image the Tails project distributes to uncover some kinds of
And by the way, not only our ISO images are now reproducible, but so are
our incremental upgrades. And you are benefiting from this improvement
without even noticing :)
Besides Mozilla's Open Source Support and the Reproducible Builds
community that provided critical help where we strongly needed it, we'd
also like to thank all members of our community who helped us test this
process. You giving us a hand is much appreciated!
If you are interested in the technical details of our implementation, we
invite you to read our [report to the Reproducible Builds
about how we did it.
We've also published technical [[instructions to
verify|/contribute/build/reproducible/#verify-iso]] one's own
Help us make Tails even better
Tails is a self organized free software project. We depend on
partnerships, grants and most importantly on donations by individuals
Care to give us a hand to make Tails bake even better cakes in the
future? <div id="donate-button"><a
Any reproducible build process is reproducible… until proven
otherwise. In our case last-minute issues were discovered and should
be fixed in the next Tails release:
- [[!tails_ticket 14933]]