Nine days ago, an email was sent on tails-dev boum.org, asking for help about building Tails in a reproductible way, and since not everyone is reading this mailing list, I thought about writing about this email here.

If you're looking for a simple (and valuable) way to help the Tails project, but have no time, can't write code, do system administration, draw, translate, design, … there is still a way: building Tails. The build process is now pretty straightforward (thanks to Vagrant and other assorted black-magic wizardry), but the big news is that it should now be possible to build Tails in a reproductible way!

This has pretty cool implications:

• The Tails dev can now rely on an untrusted third party for the whole release process, and only check at the end that the checksum of the image is the same, and if it is, to sign it, without having to hand the holy signing keys to the aforementioned party.
• Everyone can check that the Tails image available for downloading was effectively built from the source, this increasing the confidence.
• It becomes trickier for an attackers to backdoor the image, since they would have backdoor the sources too.

This feature being still in an experimental stage, it would be super-nice if you could run a couple of commands, and try to build the exact same image than the official Tails 3.1 one! It doesn't take long, your feedback is super valuable, it only takes some disk space and CPU, … you don't have any excuse for not giving it a try.

The verbatim email is below, have fun!

Dear Tails and Tor contributors, dear Reproducible Builds community,

As you might know, Tails has received the Mozilla Open Source Software award (MOSS) to make Tails ISO images build reproducibly. Since this project has started, less than a year ago, we've made huge progress and we've finally seen some ISO images build reproducibly on the build environments of our core developers as well as on our isobuilder machines. (See our previous reports).

However, there are still some remaining issues which we'd like to know more about in order to fix them. That's why we are asking for your help: Please try and build the Tails 3.1 ISO image and report your findings back to us. You will find all instructions for doing so hereafter. Please don't hesitate to contact us if you get stuck at some point in the process, for example by connecting to our chatroom. You can also send us email to tails-dev at boum.org (public) or tails at boum.org (private).

How?

For your convenience all instructions needed to attempt to reproduce Tails 3.1 are included hereafter. However all commands are adapted for Debian Stretch (and Buster/Sid), so your results may vary if you run another Linux distribution. Our full build instructions might help if you are having problems.

Setup the build environment

Building Tails requires the KVM virtual machine hypervisor to be available, a minimum of 1 GiB of free RAM and a maximum of 20 GB of free storage.

Install dependencies

sudo apt-get install \
    git \
    rake \
    libvirt-daemon-system \
    dnsmasq-base \
    ebtables \
    qemu-system-x86 \
    qemu-utils \
    vagrant \
    vagrant-libvirt \
    vmdebootstrap && \
sudo systemctl restart libvirtd

If building as a non-root user

(Skip this section if you intend to build Tails as the root user!)

Make sure that the user that is supposed to initiate the build is part of the relevant groups:

for group in kvm libvirt libvirt-qemu; do sudo adduser $user $group; done

Then run newgrp (or just reboot) to apply the new group memberships to the session.

Build Tails 3.1

git clone https://git-tails.immerda.ch/tails
cd tails
git checkout 3.1
git submodule update --init
rake build

Send us feedback!

No matter how your build attempt turned out we are interested in you sending us feedback. For that we'll first need some information of the system you used -- please run these commands in the exact same terminal session that you ran rake build in (e.g. run them right after rake build)!

sudo apt install apt-show-versions || :
(
    for f in /etc/issue /proc/cpuinfo
    do
    echo "--- File: ${f} ---"
    cat "${f}"
    echo
    done
    for c in free locale env 'uname -a' '/usr/sbin/libvirtd --version' \
            'qemu-system-x86_64 --version' 'vagrant --version'
    do
    echo "--- Command: ${c} ---"
    eval "${c}"
    echo
    done
    if which apt-show-versions >/dev/null
    then
    echo '--- APT package versions ---'
    apt-show-versions qemu:amd64 linux-image-amd64:amd64 vagrant \
                        libvirt0:amd64
    fi
) | bzip2 > system-info.txt.bz2

Please have a look at the generated file with

bzless system-info.txt.bz2

to make sure it doesn't contain any sensitive information you do not want to leak in case you send this file to us or make it public!

Next, please follow the instructions below that match your situation!

If the build failed.

Please open a ticket on our bug tracker with "Category" set to "Build system" and system-info.txt.bz2 attached (note that this makes this file public).

If the build succeeded ...

Please compute the SHA-512 checksum of the resulting ISO image:

sha512sum tails-amd64-3.1.iso

and compare it to:

843427fa13446c4b7134a10d3269b693317bbb898759e9d4e5dd8a25583372bed767e575974f5ca0229f1b44a99d4c7b64872c3dc433c0caf8965961cac9fb30

Use the SHA256sum from our signed upgrade files instead

This is optional, but if you want to use an authenticated checksum, you can find the sha256 checksum in our upgrade files: https://tails.boum.org/upgrade/v1/Tails/3.0.1/amd64/stable/upgrades.yml .. which are signed by the Tails signing key: https://tails.boum.org/upgrade/v1/Tails/3.0.1/amd64/stable/upgrades.yml.pgp

The SHA256 checksum should be: 0ef1c7d880308ee9f98c255b2658b75445cc84622eae2944a342dcc50cea71c7

... and the checksums match (i.e. reproduction succeeded).

Congrats for successfully reproducing Tails 3.1! Please send an email to tails-dev at boum.org (public) or tails at boum.org (private) with the subject "Reproduction of Tails 3.1 successful" and attach system-info.txt.bz2 to it.

... and the checksums differ (i.e. reproduction failed).

Now you are in a great position to help Tails improve its reproducibility! Please install diffoscope version 83 or higher. If you run Debian Stretch, that is:

echo 'deb http://ftp.debian.org/debian stretch-backports main' \
    | sudo tee /etc/apt/sources.list.d/stretch-backports.list && \
sudo apt update && \
sudo apt -o APT::Install-Suggests="true" \
            -o APT::Install-Recommends="true" \
            install diffoscope

Then download the official Tails 3.1 ISO image and compare it to yours:

diffoscope \
    --text diffoscope.txt \
    --html diffoscope.html \
    --max-report-size 262144000 \
    --max-diff-block-lines 10000 \
    --max-diff-input-lines 10000000 \
        path/to/official/tails-amd64-3.1.iso \
        path/to/your/tails-amd64-3.1.iso && \
bzip2 diffoscope.*

Please send an email to tails-dev at boum.org (public) or tails at boum.org (private) with the subject "Reproduction of Tails 3.1 failed" and attach system-info.txt.bz2 to it. We also want you attach one (the smallest!) of diffoscope.txt.bz2 and diffoscope.html.bz2 to the email, but if they are "big" (say >100 KiB) then please don't bomb our mail inboxes! Instead upload the file to some web-based file-sharing service (we'd recommend RiseUp) and include the link(s) in the email.

Thank you very much for your interest and help!

Cheers! The Tails project