reproducible-signal

Since version 3.15.0 Signal for Android has supported reproducible builds. This is achieved by replicating the build environment as a Docker image. You'll need to build the image, run a container instance of it, compile Signal inside the container and finally compare the resulted APK to the APK that is distributed in the Google Play Store.

This script automates that.

Ubuntu 18.04 - TL;DR

1. Enable developer options and USB debugging on your phone.
2. Connect your phone to the computer via USB.
3. Run the commands below and follow the instructions.

mkdir -p "$HOME/reproducible-signal"
cd "$HOME/reproducible-signal"
wget https://raw.githubusercontent.com/oittaa/reproducible-signal/master/reproducible-signal.sh
chmod +x ./reproducible-signal.sh
./reproducible-signal.sh

The script might take several minutes to complete. If everything went right and the APKs match, the last line of output will be APKs match!

Ubuntu 18.04 details

1. You will need around 10GB of free space for Docker images and Signal build process
2. Required packages can be installed manually sudo apt install aapt adb docker.io unzip wget
3. If you had to install Docker
   1. Add yourself to the group sudo usermod -aG docker $USER
   2. Reboot your computer before continuing.

You can compare a previously extracted APK without connecting your phone.

./reproducible-signal.sh /path/to/signal.apk

What if I don't have a USB cable?

Many different apps can extract installed APKs. Here's an example how to get the APK to your computer with Files by Google and Google Drive.

1. Open Files by Google
2. Tap Browse
3. Tap Apps
4. Under Installed apps scroll down to Signal
5. On it's right side expand the options and select Share
6. Tap Save to Drive.
7. Set Document title to something like Signal.apk and tap Save
8. Now you can download the APK to your computer from Google Drive

Windows / macOS / other

Probably the easiest way to use this script is to install a virtual machine with Ubuntu 18.04 on it. Then follow the instructions for Ubuntu 18.04.

At least Windows 10 with VirtualBox worked flawlessly. Just remember to attach the phone to the vm!