sudo apt update
sudo apt install -y dirmngr
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-key 8B48AD6246925553
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-key 7638D0442B90D010
echo "deb http://ftp.debian.org/debian stretch-backports main contrib non-free" \
| sudo tee /etc/apt/sources.list.d/backports.list
sudo chmod 644 /etc/apt/sources.list.d/backports.list